US20160105054A1 - High-current battery management system - Google Patents

High-current battery management system Download PDF

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US20160105054A1
US20160105054A1 US14975351 US201514975351A US2016105054A1 US 20160105054 A1 US20160105054 A1 US 20160105054A1 US 14975351 US14975351 US 14975351 US 201514975351 A US201514975351 A US 201514975351A US 2016105054 A1 US2016105054 A1 US 2016105054A1
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battery
current
microcontroller
voltage
apparatus
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US14975351
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Michael S. Horito
Zack D. Bomsta
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Rocketship Inc
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Rocketship Inc
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H01M10/4257Smart batteries, e.g. electronic circuits inside the housing of the cells or batteries
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60LELECTRIC EQUIPMENT OR PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES, IN GENERAL
    • B60L11/00Electric propulsion with power supplied within the vehicle
    • B60L11/18Electric propulsion with power supplied within the vehicle using power supply from primary cells, secondary cells, or fuel cells
    • B60L11/1851Battery monitoring or controlling; Arrangements of batteries, structures or switching circuits therefore
    • B60L11/1861Monitoring or controlling state of charge [SOC]
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4207Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells for several batteries or cells simultaneously or sequentially
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48Accumulators combined with arrangements for measuring, testing or indicating condition, e.g. level or density of the electrolyte
    • H01M10/482Accumulators combined with arrangements for measuring, testing or indicating condition, e.g. level or density of the electrolyte for several batteries or cells simultaneously or sequentially
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0029Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety devices
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0029Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety devices
    • H02J7/0031Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety devices using battery or load disconnect circuits
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/007Regulation of charging current or voltage
    • H02J7/0072Regulation of charging current or voltage using semiconductor devices only
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/007Regulation of charging current or voltage
    • H02J7/0072Regulation of charging current or voltage using semiconductor devices only
    • H02J7/0088Regulation of charging current or voltage using semiconductor devices only the charge cycle being terminated in response to non-electric parameters
    • H02J7/0091Regulation of charging current or voltage using semiconductor devices only the charge cycle being terminated in response to non-electric parameters in response to temperature of the battery
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H01M2010/4271Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H01M2010/4278Systems for data transfer from batteries, e.g. transfer of battery parameters to a controller, data transferred between battery controller and main controller
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M2220/00Batteries for particular applications
    • H01M2220/20Batteries in motive systems, e.g. vehicle, ship, plane
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0029Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety devices
    • H02J2007/004Overdischarge protection

Abstract

An apparatus includes a microcontroller and isolation circuitry including multiple transistor-based switches arranged electrically in parallel to isolate a battery from a load source, wherein the battery is capable of providing high levels of current. The apparatus includes a first buss bar to which first pins of the multiple switches are connected, wherein the first buss bar is to be connected to the battery and a second buss bar to which second pins of the multiple switches are connected, wherein the second buss bar is to be connected to the load source. A microcontroller is programmed to control the multiple switches substantially simultaneously to isolate the battery from the load source upon detecting a predetermined condition.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • This application is a continuation-in-part of PCT/US2014/40997, filed Jun. 5, 2014, which claims the benefit of U.S. Provisional Patent Application No. 61/836,233, filed Jun. 18, 2013, wherein the entire disclosure of both applications are incorporated herein by this reference.
  • BACKGROUND
  • 1. Technical Field
  • The present disclosure relates generally to the management and protection of batteries, and more specifically to a high-current battery management system.
  • 2. Description of Related Art
  • Lead Acid batteries are the common battery of choice for starting internal combustion engines (ICE) vehicles. Lead acid batteries are robust in that they can handle a fair number of charge-discharge cycles and can operate in most non-extreme environmental temperature ranges. While they do degrade when over-discharged, the effect is not as drastic as other chemistries. Furthermore, lead-acid batteries are comparatively low cost compared to other types of batteries.
  • However, other chemistries, such as lithium iron phosphate (LFP) have advantages over lead-acid batteries. Although there are several chemistries that can have these advantages over lead-acid batteries, LFP is generally referred to herein by way of example only, and is not meant to be limiting. Batteries using other chemistries, such as LFP, typically consist of a battery pack made up of multiple cell banks arranged electrically in series to achieve the voltage output desired. Furthermore, a cell bank can consist of one cell, or multiple cells arranged electrically in parallel to achieve the capacity level, or ampere-hour (Ah), desired.
  • Advantages of using another chemistry, such as LFP, over lead-acid particularly for starting ICE vehicles, include by way of example, substantially longer cycle lives, so the batteries can last much longer (around three to six times longer by most estimations). Batteries other than lead-acid batteries also have higher energy density, which allows the battery to be more compact than a lead-acid battery while still maintaining the same capacity (e.g., number of Ah). An LFP battery pack could be less than one half the size of a lead-acid battery and still contain the same amount of capacity.
  • The advantages of other-than-a-lead-acid battery also includes less internal resistance, so less capacity is needed to achieve the desired cranking amperes (“amps”). A lead-acid battery with higher internal resistance requires that the battery bank be over-sized in order to achieve the necessary high surge current required to start an engine. One explanation for why this works is the surge current can be distributed between cells connected electrically in parallel, reducing the voltage drop as current passes over the internal resistance according to Ohm's law (V=IR) over each individual cell's internal resistance. Another explanation is the fact that putting multiple cells or banks in parallel reduces the overall effective internal resistance of the power source according to the parallel impedance equation:
  • 1 Z eq = 1 Z 1 + 1 Z 2 + + 1 Z n .
  • The lower internal resistance of the LFP battery results in the capability of the battery to provide the required high surge current with much less capacity. Because less capacity is needed, the volumetric size of the battery can be reduced even further (approximately 50%-75% smaller). For example, because a lead-acid battery has much higher internal resistance, a typical semi-truck may require a lead-acid bank with a capacity of up to 280 Ah to achieve the necessary cranking amps required to start the engine. This would require three to four lead-acid batteries taking up approximately six to eight cubic feet. An LFP battery with much lower internal resistance would only require a capacity of 46 Ah to start the same engine, and take up approximately a cubic foot in comparison.
  • Other advantages of other-than-lead-acid batteries further include being of lighter weight, making it easier to handle and less weight for the vehicle to carry. The lead-acid batteries for a semi-truck weigh approximately 200 pounds (lbs.) total while an LFP battery for starting the same vehicle may weigh only about 20 lbs.
  • Also, an LFP battery includes no hydrogen off-gassing (so less chance for explosion) and no sulphation, so no corrosion or corrosive leakage. Off-gassing, also referred to as outgassing, is the emission of especially noxious gases that is dissolved, trapped, frozen or absorbed in some material. Off-gassing can include sublimation and evaporation which are phase transitions of a substance into gas as well as desorption, seepage from cracks or internal volumes and gaseous products of slow chemical reactions. Sulphation is the normal movement of the sulfate radical SO4, from the sulfuric acid electrolyte H2SO4, to the battery plates during the discharge and re-charging cycle of a rechargeable battery.
  • An LFP battery, however, is not as robust as a lead-acid battery when it comes to over-discharging or overheating. Additionally, lower internal resistance and the habit to have a smaller capacity battery also creates both a safety concern as well as a need to protect and optimize the operational life of the battery.
  • As mentioned above, today's lead-acid battery banks used for starting a semi-truck are over-sized in order to achieve the desired cranking amps. This results in a large amount of excess capacity in the battery bank. Because LFP requires less capacity to achieve needed cranking amps, LFP batteries have considerably less excess capacity available for other things. For example, it is common for drivers to turn off their engines while stopping for rest, yet continue to use running lights, cab lights, fans, radios and other appliances. Because the lead-acid battery bank contains a large amount of excess capacity, it can provide this power for a certain length of time. However, because the LFP battery has much less capacity, there is much less excess capacity to use for such loads. If the driver were to use the same appliances, they would increase the risk of running down the battery and over-discharging it and increasing the likelihood of a dead battery. Once over-discharged, an LFP battery degrades much faster than a lead-acid battery, reducing the operational life to less than that of a lead-acid battery.
  • Additionally, if the battery system were to experience a short circuit, the effect would be even more catastrophic than if a lead-acid battery system short circuits. The lower internal resistance allows for higher surge currents that can cause much greater damage than seen in lead-acid batteries. For example, if a cable were to wear through its protective sheathing and contact any metal on the truck, such as the frame or other wiring, the entire battery system could instantaneously become red hot and the metals reach their melting point. The LFP battery could also begin to overheat at a rate much higher and to temperatures much higher than in lead-acid batteries. Typically, the result would lead to a fire in the vehicle, either from the battery itself bursting into flames, or other parts of the vehicles become overheated and combusting.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • The disclosure will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the disclosure. The drawings, however, should not be taken to limit the disclosure to the specific embodiments, but are for explanation and understanding only.
  • FIG. 1 is a perspective view of a buss bar according to one embodiment.
  • FIG. 2 is a perspective view a circuit board with a bottom buss bar attached, according to one embodiment.
  • FIG. 3 illustrates a battery management system (BMS) assembly as in FIG. 2, with subarrays of metal-oxide semiconductor field-effect transistors (MOSFETs) and a top buss bar attached, according to one embodiment.
  • FIG. 4 illustrates a BMS assembly as in FIG. 3, but with bottom and top buss bars according to another embodiment.
  • FIG. 5 illustrates a BMS assembly as in FIG. 3, with a heat tie added on top of the MOSFET arrays according to one embodiment.
  • FIG. 6 illustrates an underside of the BMS assembly of FIG. 5 with metal oxide varistors (MOVs) and cell balancing circuitry, according to one embodiment.
  • FIG. 7 is a block diagram of circuitry of a battery management system (BMS) located at least in part on the circuit board of FIGS. 2-6, according to one embodiment.
  • FIG. 8 is a circuit diagram of a MOSFET array attached between the top and bottom buss bars of FIGS. 1-6, according to one embodiment.
  • FIG. 9 is a circuit diagram of the MOSFET switching driver of the battery management system of FIG. 7, according to one embodiment.
  • FIG. 10 is a circuit diagram of the surge detection circuit of the battery management system of FIG. 7, according to one embodiment.
  • FIG. 11 is a circuit diagram of the surge measuring circuit of the battery management system of FIG. 7, according to one embodiment.
  • FIG. 12 is a circuit diagram of the buss bar temperature sensor of the battery management system of FIG. 7, according to one embodiment.
  • FIG. 13 is a circuit diagram of the cell bank voltage sensor of the battery management system of FIG. 7, according to one embodiment.
  • FIG. 14 is a circuit diagram of a voltage divider that measures the charge of an entire battery bank (e.g., cell pack) of the battery management system of FIG. 7, according to one embodiment.
  • FIG. 15 is a circuit diagram of charge shunt circuitry of the battery management system of FIG. 7, according to one embodiment.
  • DESCRIPTION OF EMBODIMENTS
  • For safety reasons, a battery management system (BMS) can protect the battery from a short circuit or overheating by isolating the battery from the load source. Additionally, in order to optimize the battery life, the BMS can also detect a low voltage and isolate the battery to prevent the battery from being over-discharged. Current LFP batteries for starting vehicles do not have such a BMS that performs this protection and isolation, which are therefore not available to average consumers.
  • The BMS can be coupled to a battery cell pack such that the BMS resides in a single enclosure, generally referred to as a battery. “Cell pack” is one or more cell banks connected in series to achieve a desired voltage output. A cell bank is one or more cells connected in parallel to achieve a desired capacity. In the alternative, the BMS can be external to the battery in its own independent enclosure and connected to the internal battery cell pack from the outside of the battery. This later configuration can be useful in aftermarket applications with a battery that was manufactured with no BMS. In either case, the BMS can be connected in line at the negative terminal of the battery such that the BMS can control the return current to the battery and shut off power from the battery, if necessary.
  • One challenge with creating a BMS for this scenario is the ability to cut a high current. A vehicle, such as a large semi-truck, can draw around 400 amps while turning over the engine. However, there is a momentary spike in the current draw when the ignition is initially attempted. This current spike can reach as high as 2,500 amps, an extremely high current. This means the BMS should be able to allow at least this much current to pass for a specified period of time without shutting off, to allow the vehicle to start properly. When an unexpected high current is detected and determined to be outside of specified safe operating ranges, the BMS is to cut the current at this very high level. Shutting off a high current like this is normally achieved with mechanical relays or insulated-gate bipolar transistors (IGBTs). These mechanical relays and IGBTs, however, are expensive and bulky, making it difficult to fit the battery configured with mechanical relays or IGBTs into the same size compartment as a standard vehicle starting battery. Use of mechanical relays or IGBTs also increases cost beyond prices comparable to existing vehicle starting batteries.
  • Using a plurality of solid state semiconductor, transistor-based switches arranged electrically in parallel in a BMS is a less expensive and a compact alternative. These transistor-based switches can include, for example, bipolar junction transistors (BJTs), metal-oxide semiconductor field-effect transistors (MOSFETs), junction field-effect transistors (J-FETs), meta-semiconductor field-effect transistors (MESFETs), or modulated-doping field-effect transistors or modulation-doped field—effect transistors (MODFETs), and the like. For ease of explanation. the present disclosure will sometimes refer to all of these as “switches.”
  • Transistor-based switches, and particularly MOSFETs, are commonly used in low current situations such as cellphones, laptops and other portable rechargeable devices (on the order of milliamps). Switches such as MOSFETs are significantly less expensive and less bulky than mechanical relays or IGBTs. However, MOSFETs are not available that can handle currents in the thousands of amps, and in these situations, designers usually employ electromechanical relays or IGBTs, which are designed for higher power applications. In one embodiment, MOSFET-based switches are significantly less expensive, and less bulky, and by using an array of transistor-based switches connected electrically in parallel it is possible to handle high current situations when the current load can be distributed and shared properly. For example, to use MOSFET-based switches in high current applications, the MOSFETs are to be protected from overloading so that the MOSFETs can reliably be used to isolate the battery from the system, as will be described in more detail.
  • Unfortunately, when transistor-based switches such as MOSFETS are manufactured, each batch of the switches has a different Vgs (gate to source voltage) or turn on voltage. Matching switches from the same batch is only achievable during the silicon wafer manufacturing process and ensuring that switches are selected from the same batch is difficult and costly and therefore not a preferred option. The difference in turn on times between batches can only be slight (measured in nanoseconds and even picoseconds), but is significant enough to make it difficult to switch the switches on/off at the same time. This time difference can cause the faster switch in the array to carry the entire load and burn up.
  • By maintaining turn on times that are as close to the same as possible among all the switches in the array, the switches can distribute the current simultaneously when cutting the current. Maintaining a similar turn on voltage across the array of switches is difficult but manageable if approached differently from common practices and recommendations for utilizing switches, as will be explained.
  • Additionally, when starting a vehicle with an electric starter motor, a very large inductive load is put on the battery that requires high current. Suddenly switching the current off with this very large inductive load creates a very fast and very large voltage spike (measured in kilovolts (kV)) that can overload the transistor-based switches, causing them to burst. If the inductive current is kept at or below recommended operating currents, the transistor-based switches can handle them fine without overheating, provided the proper thermal heat sinking is used. While transistor-based switches are sensitive to overcurrent and overvoltage conditions, transistor-based switches can be employed in a BMS as disclosed herein when these conditions are properly controlled.
  • In one embodiment, a rechargeable battery system of the present disclosure includes a battery pack and a battery management system (BMS). The battery pack has rechargeable battery cells that are connected in a way that allows the battery cells to be discharged when the battery system is in operation. The BMS is connected to the battery to allow data gathering from the battery, and to provide selective isolation between the battery and a load source. The BMS can be configured to perform cell balancing within the battery bank. Cell balancing allows each of the rechargeable battery cells to be maintained in a similar electrical state.
  • In still other embodiments, the BMS can include isolation circuitry. The isolation circuitry can be configured to electrically isolate the battery when a threatening electrical system event, for example a short circuit, is detected within or even outside of the battery system. For example, a battery system is designed with a battery pack containing rechargeable battery banks and cells, and a BMS can be connected to the battery pack.
  • For example, a BMS can include isolation circuitry including multiple, transistor-based switches arranged electrically in parallel to isolate a battery from a load source, wherein the battery is capable of providing high levels of current of at least 400 amperes. The BMS can further include a switching driver circuit operatively coupled to the isolation circuitry such as to switch off the multiple switches simultaneously. The BMS can further include a microcontroller operatively coupled to the switching driver circuit and configured to direct the switching driver circuit to turn off the multiple switches responsive to detecting a predetermined condition
  • In one embodiment, the microcontroller directs the switching driver circuit to switch off the multiple switches at substantially the same time, and other circuit design techniques can be used to synchronize the timing of turning the multiple switches on and off. The structure and programmed control provide this timing in order to distribute the load evenly, to prevent damage caused by overvoltage, as will be discussed in more detail.
  • In another embodiment, a BMS can include isolation circuitry including multiple, transistor-based switches arranged electrically in parallel to isolate a battery from a load source, wherein the battery is capable of providing high levels of current. The BMS can further include a first buss bar to which first pins of the multiple switches are connected, wherein the first buss bar is to be connected to the battery and a second buss bar to which second pins of the multiple switches are connected, wherein the second buss bar is to be connected to the load source. A microcontroller of the BMS can be programmed to control the multiple switches substantially simultaneously responsive to detecting a predetermined condition. For example, the microcontroller can receive a signal indicating any number of conditions, such as a short circuit in the load source, overheating of the battery, overheating of the isolation circuitry, a low-voltage threshold of the battery, or a user-initiated shut off, among other as will be discussed.
  • In yet another embodiment, the BMS can further include a surge detection circuit including an operation amplifier to detect a surge in current by measuring a voltage difference between source and drain of a subset of the multiple switches. The BMS can further include a surge measuring circuit to measure a magnetic field and to determine a current level of the surge in current. The microcontroller can be operatively coupled to the surge detection circuit and the surge measuring circuit, wherein the microcontroller is to: receive a first signal from the surge detection circuit, wherein the first signal is indicative of detecting the surge in current; turn on the surge measuring circuit responsive to the signal; receive the current level of the surge from the current measuring circuit; and send a second signal to switch off the multiple switches responsive to determining that the current level is above a pre-defined threshold current level indicating a short circuit. In one embodiment, the surge measuring circuit includes a Hall Effect sensor attached to a circuit board with which to measure the magnetic field.
  • These and other features will now be explained in more detail that help to prevent individual transistor-based switches from overcurrent and overvoltage conditions by synchronizing turn on times, and other solutions that reduce the effects of voltage spikes, short circuits and the like.
  • FIG. 1 is a perspective view of a buss bar 100 according to one embodiment. The buss bar 100 can include a single conductive path (or two co-conductive paths) as in FIG. 4, or as in FIG. 1, a first conductive path 102 a and a second conductive path 102 b that connect to each other. As shown in FIG. 1, the first conductive path 102 a and the second conductive path 102 b can form a horseshoe shape, although other shapes are envisioned that likewise provide two conductive paths, such as a V-shape, a square or rectangular shape and the like. The buss bar 100 can also include a number of apertures through which to connect the buss bar 100 to a battery pack or to a load source, e.g., a vehicle when the battery pack (or battery) is to turn on and power the vehicle. In the description herein, battery pack and battery can be used interchangeably to refer to a source of stored power deliverable as current to a load source. In some cases, however, the term battery can be considered to include a battery pack made up of banks of storage cells.
  • FIG. 2 is a perspective view a circuit board 200 with a bottom buss bar 100 a attached to the circuit board 200, according to one embodiment. A number of electrical and sensing components can be attached to the circuit board 200 that perform or help perform a number of isolation and protection functions as well as communication and monitoring functions. For example, a first metal trace 202 a and a second metal trace 202 b (one for each sub-array of switches that is arranged along each conductive path 102 a and 102 b, respectively) can be formed on the circuit board 200. Additional components, which will be discussed in more detail with reference to FIGS. 7-14, include but are not limited to a switching driver circuit 204, a microcontroller 206, Hall Effect sensors 210 a and 210 b, a satellite board connector 214, a data port 216 (e.g., a universal serial bus (USB) connector), wireless circuitry 220, global positioning system (GPS) circuitry 224, a reset button 228 to allow the user to reconnect the battery to the system if pre-determined requirements are met, a light emitting diode (LED) (or other type of) display 230 to provide status indications and instructions to an operator, and a temperature sensor 234.
  • The satellite board connector 214, the data port 216, the wireless circuitry 220 and the GPS circuitry 224 can also act as a communication interface in various embodiments that enables communications via one or more communications networks. A communication network can include wired networks, wireless networks, or combinations thereof. Such a communication interface over the communications network(s) can enable communications via any number of communication standards, such as 802.11, 802.17, 802.20, WiMax, 3G, 4G, long term evolution (LTE) or other cellular telephone or communication standards.
  • FIG. 3 illustrates a battery management system (BMS) assembly 300 as in FIG. 2, further illustrating an array 304 of solid state semiconductor switches such as multiple transistor-based switches 302, which sometimes are referred to as switches 302 for ease of explanation. The array 304 of switches 302 can further be broken down into two subarrays of switches. These two subarrays can include a first subarray 308 a and a second subarray 308 b of transistor-based switches 302 connected to the circuit board 200 and between the bottom buss bar 100 a and a second (or top) buss bar 100 b. In a typical configuration, the bottom buss bar 100 a is to be connected to the battery and the top buss bar 100 b is to be connected to the load source, although these can be switched in another embodiment. In one embodiment, the first subarray 308 a and the second subarray 308 b each include an equal number of switches, thus balancing the current load on the first switches closest to the load source across multiple subarrays of switches.
  • In other words, when the current travels through a buss bar, the current arrives at the first switch on the buss bar (the one closest to the load source) sooner than it arrives at the last switch in the line. Although seemingly negligible, this time difference can cause the first switch to overload and burst before the current is equalized across the array of switches in high current applications. Accordingly, this time difference can be reduced by arranging multiple subarrays 308 a and 308 b of equal numbers of electrically parallel switches 302 along each of the multiple electrically parallel conductive paths of the buss bars. The relief to each first switch of each subarray is proportional to the number of subarrays of switches arranged in parallel, so it is envisioned that more than two subarrays 308 a and 308 b could be employed.
  • With further reference to FIG. 3, the switches 302 of the first subarray 308 a can be arranged in a line along an edge of the first conductive path 102 a and of the second subarray 308 b can be arranged in a line along an edge of the second conductive path 102 b. In one embodiment, the edges can oppose each other so that at least the first switch from each of the two different subarrays are located equidistant from the battery (along the bottom buss bar 100 b) and are located equidistant from the load source (along the top buss bar 100 a). In this way, first current moving between the first subarray 308 a and the battery can arrive at substantially the same time as second current moving between the second subarray 308 b and the battery. Similarly, third current moving between the first subarray and the load source can arrive at substantially the same time as fourth current moving between the second subarray 308 b and the load source. This works to further synchronize the time at which the switches are loaded. This method alone (synchronizing the time at which the current reaches the switches), however, may not necessarily be enough to protect the switches from overloading, particularly in ultra-high current situations.
  • FIG. 4 illustrates a BMS assembly 400 as in FIG. 3, but with a bottom buss bar 400 a and a top buss bar 400 b according to another embodiment. In this embodiment, each buss bar 400 a and 400 b can be considered to have a single conductive path, or two co-conductive paths. The co-conductive paths of each buss bar 400 a and 400 b are still connected, however, and provide opposing edges along which to position the first subarray 308 a and the second subarray 308 b of switches 302, respectively.
  • In one embodiment, the source pin of each transistor-based 302 switch is connected to the bottom buss bar 100 a or 400 a and the drain pin of each switch 302 is connected to the top buss bar 100 b or 400 b. In another embodiment, these connections are switched. The circuit board 200 can include holes through which each source pin can pass to connect to the bottom buss bar 100 a located beneath the circuit board 200. In one embodiment, the first pins of the switches are of equal length and the second pins of the switches are equal length, to further synchronize the timing of current arriving at the switches 302 of respective subarrays 308 a and 308 b.
  • In one embodiment, the metal traces 202 a and 202 b (of FIG. 2 and now hidden in FIG. 3) can connect gates of the transistor-based switches 302 to a switching driver circuit 204 and be electrically equidistant from the switching driver circuit 204, which controls switching the semiconductor switches on and off as directed by a microcontroller 206 (see also FIG. 7). This is referred to as trace matching, and can be tuned such that the arrival of an on/off signal at any two switches 302 is as close to the exact moment as possible, where even a few nanosecond can be too much time. This is the case particularly with high current, where a difference of too much time could cause one switch to quickly conduct too much current (an overcurrent situation), overloading the switch and causing it to burst before other switches in the array can divert some of that current. However, synchronizing the timing of the signal with metal tracing alone is not necessarily enough to protect the switches from overcurrent.
  • FIG. 5 illustrates a BMS assembly 500 as in FIG. 3, with a heat tie 502 added on top of the subarrays 308 a and 308 b of transistor-based switches 302 according to one embodiment. The heat tie 502, also referred to as a heat conducting bar, can be thermally coupled to the switches to equalize the temperature across the switches 302. In one embodiment the heat tie 502 is made of an appropriately-sized heat conducting material meant to equalize heat across the heat tie and thus across the switches. Equalizing the temperature across the switches 302 allows the temperature of each switch to be as close to the same as the temperature of any other switch. This is beneficial because temperature impacts the turn on voltage (Vt), which can be expressed as:
  • V T = V FB + 2 φ F + 2 s 5 qN a ( 2 φ F + V SB C ox .
  • The φF parameter can be significantly affected by temperature and which represents half the surface potential of the switches. The equation for φF, expressed as

  • φF =(kT/q)ln(N A /N i)
  • shows the dependency on temperature T. As T increases, φF also increases, causing the turn on voltage to increase. This means that if one switch is cooler than another, then the one switch will turn on more quickly as the turn-on signal (gate voltage) does not have to rise to as high of a value to overcome the turn-on voltage. Accordingly, temperature differences between the switches affect the ability of the BMS to turn on or off the switches at substantially the same time, and avoid an overcurrent condition on any individual switch that could cause the switch to burn out. Only equalizing the temperature across all the switches, however, may not necessarily protect against all overcurrent situations.
  • FIG. 6 illustrates an underside of the BMS assembly 500 of FIG. 5 with metal oxide varistors (MOVs) 607 a and 607 b and bank balancing circuitry 603, according to one embodiment. The bank balancing circuitry 603 will be discussed in more detail with reference to FIG. 7. Where slower switching alone may not reduce the voltage spike enough to protect the switches 302 from overvoltage and damage, any remaining voltage spikes can be shunted away from the switches 302 to further protect the switches from damage.
  • The MOVs 607 a and 607 b can be used to provide voltage suppression to protect the switches 302 from overvoltage by shunting the current caused by high voltages away from the switches 302. An MOV is a variable resistor, which increases in resistance at low voltages and decreases in resistance at high voltages. By placing the MOV electrically in parallel with the switches, the high resistance during normal operation will not shunt a significant amount of current away from the switches. However, because resistance of the MOV decreases at high voltages, a voltage spike can effectively turn the MOV into a short circuit and shunt the current away from the switches 302 so as not to overload the switches. Using only MOVs to suppress voltage spikes may not necessarily be sufficient to protect the switches from overvoltage situations. For example, combining the MOVs 607 a and 607 b with slow switching of the switches 302 can be used to more reliably protect the switches from overvoltage.
  • FIG. 7 is a block diagram of circuitry of a battery management system (BMS) 700 located at least in part on the circuit board of FIGS. 2-6, according to one embodiment. Additional or fewer components are contemplated in additional embodiments, and as will be apparent herein. The BMS 700 can include the MOSFET subarrays 308 a and 308 a and attached bottom buss bar 100 a or 400 a and top buss bar 100 b or 400 b that can be coupled between a battery 705 and a load 715. The battery 705 can include multiple cell banks, including in the illustrated embodiment, Bank_1, Bank_2, Bank_3 and Bank_4, to increase voltage output. A more-detailed circuit diagram of the array 304 of switches 302, the bottom buss bar 100 a or 400 a, and the top buss bar 100 b or 400 b is shown in FIG. 8, according to one embodiment.
  • The microcontroller 209 can receive sensor signals and other information with which to manage and monitor the battery and other potentially unsafe conditions. Voltage and current levels along with other parameters and features can be stored in a memory 207 for later retrieval by the microcontroller 209. The memory 207 can be computer-readable media. A “computer-readable medium,” “computer-readable storage medium,” “machine readable medium,” “propagated-signal medium,” and/or “signal-bearing medium” can include any device that includes, stores, communicates, propagates, or transports software for use by or in connection with an instruction executable system, apparatus, or device. The machine-readable medium can selectively be, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium.
  • Accordingly, the BMS 700 and methods disclosed herein can be realized in hardware, software, including firmware, or a combination of hardware and software. The BMS 700 and methods can be realized in a centralized fashion in at least one BMS or in a distributed fashion where different elements are spread across several interconnected BMSs. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. The BMS 700 and methods can also be embedded in a computer program product, which includes all the features enabling the implementation of the operations described herein and which, when loaded in a BMS of sufficient capability, is able to carry out these operations. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a BMS having an information processing capability to perform a particular function, either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.
  • With continued reference to FIG. 7, the BMS 700 can further include the switching driver circuit 204 operatively coupled between the microcontroller 209 and the switches 302 of the subarrays 308 a and 308 b. A more-detailed circuit diagram of the switching driver circuit 204 is shown in FIG. 9, according to one embodiment. An on/off signal from the microcontroller 209 comes into the switching driver circuit 204 and a battery on/off signal is output from the switching driver circuit 204, to turn off the switches 302 as discussed herein. The switching driver circuit 204 can amplify the signal from the microcontroller 209 and slow the switching speeds to reduce current spikes.
  • For example, when suddenly switching off high currents with a large inductive load, as is done with a high-current battery for example, the battery can experience very large voltage spikes (in the kV range). These spikes can overload the switches 302 and cause the switches to burst. The size of the voltage spike depends on the equation for the voltage across an inductor, expressed as:
  • υ = t ( Li ) = L i t .
  • which states that the voltage is equal to the rate of change of the current times the inductance. The faster the current changes, the higher the voltage spike.
  • To reduce the rate of change of current (when the switches are switched off), and thereby reduce overvoltage due the voltage spike, switching circuitry in the switching driver circuit 204 can be designed or programmed to turn the switches 302 on and off at speeds as slow as possible, to reduce the change in current over time without exceeding the maximum allowable power dissipation caused by switching (switching causes the highest power dissipation in most types of transistors including MOSFETS). In one embodiment, for example, component values of a resistive-capacitive (RC) circuit of the switching driver circuit 204 can be set to a specific rise time for the turn on/off signal. This setting is well below the manufacturers recommendations. It is commonly held that transistor-based switches such as MOSFETs should switch off as fast as possible, so switching as slow as possible is a counter intuitive approach. Only slowing the switching speed, however, may not necessarily protect all of the switches from overvoltage due to voltage spikes.
  • The BMS 700 can further include a surge detection circuit 713 located on the circuit board 200 and operatively coupled to the microcontroller 209 to provide a first-stage surge detection. In one embodiment, the surge detection circuit 713 also operates as a current sensing circuit. A more-detailed circuit diagram of the surge detection circuit 713 is illustrated in FIG. 10, according to one embodiment. A dual operational-amplifier (op-amp) circuit 1010 can send an I_SENSE_ON signal to indicate to the microcontroller 209 to turn on a surge measuring circuit 710. The op-amp circuit 101 can provide initial, low-power current sensing by measuring a voltage difference between source and drain of a subarray of electrically parallel switches, e.g., subarray 308 a and/or subarray 308 b, and calculating the current based on the switches' specific voltage-current characteristics. The calculated current can be sent to the microcontroller 209 through the Vdrain_G6 pin.
  • A digital-to-analog converter (ADC) 709 may be included to help convert the current to a digital signal readable by the microcontroller 209. In different embodiments, the ADC 709 can be integrated into the microcontroller 709 (as shown) or into the surge detection circuit 713, or can be a stand-alone ADC 709 on the circuit board 200.
  • Upon detecting a sufficient surge in current, the I_SENSE_ON signal can alert the microcontroller that a current over a predetermined threshold (e.g., 10, 15 or 25 amps or the like) has been detected. The microcontroller 209 can then turn on Hall Effect sensors 210 a and 210 b to more accurately measure how much current the surge contains, to help distinguish between, for example, an engine start and a short circuit as will be discussed in more detail.
  • For example, the BMS 700 can further include the surge measuring circuit 710, which can include a left Hall Effect sensor 210 a and a right Hall Effect sensor 210 b, attached to the circuit board 200 and operatively coupled to the microcontroller 209. A more-detailed circuit diagram of the left Hall Effect sensor 210 a of the surge measuring circuit 710 is illustrated in FIG. 11, according to one embodiment. A Hall Effect voltage (Vhall), which represents the magnitude of the magnetic field created by the buss bar current that is sensed, is output to the microcontroller 209. The microcontroller 209 can then determine whether or not the Vhall value is within operating ranges and take appropriate action that may be necessary, such as switching off the transistor-based switches 302.
  • The BMS 700 can further include the temperature sensor 234, locatable between the circuit board 200 (FIGS. 2-6) and at least one buss bar, and which is also operatively coupled to the microcontroller 209. A more-detailed circuit diagram of the temperature sensor 234 is illustrated in FIG. 12, according to one embodiment. The buss bar temperature is output from the temperature sensor 234 to the microcontroller 209.
  • The BMS 700 can further include the bank balancing circuitry 603 and corresponding bank voltage sensors 703 operatively coupled between the microcontroller 209 and the banks within the battery 705. A more-detailed circuit diagram of the bank voltage sensors 703 is illustrated in FIG. 13, according to one embodiment. A voltage output for each bank of the battery 705 is sent to the microcontroller 209. An example voltage divider 1400 as illustrated in FIG. 14 can be used to measure a charge the entire battery pack, e.g., battery 705. Dividing the voltage down to a lower voltage can allow the microcontroller 209 or the ADC 709 to properly handle or operate on the lower voltages.
  • Furthermore, a more-detailed circuit diagram of the bank balancing circuitry 603, with separate circuits 603 a, 603 b, 603 c and 603 d to balance, respectively, Bank_1, Bank_2, Bank_3 and Bank_4 within the battery 705 is illustrated in FIG. 15 according to embodiment. Each balancing circuit receives a corresponding bank control signal from the microcontroller 209.
  • With it now possible to consistently protect the array 304 of transistor-based switches from damage due to overcurrent or overvoltage situations, the array 304 can be reliably used as an isolation circuit. A microcontroller 209 can be operatively coupled to the isolation circuitry to control when current is allowed to pass and when it is cut off, or in other words, when the battery should be connected to a loud source (or other electrical system) and when it should be isolated from the load source. Voltage sensors, temperature sensors and other such sensors or sensing devices that can detect an event and send a signal to the microcontroller 209 can be used to help the microcontroller 209 know when to allow current to pass though the battery 705, and whether to cut off current through the battery due to an unsafe condition as defined by the micro-controller's programming. In the case of a starter battery, we protect against certain events that could create a dangerous situation or reduce the life of a battery as now explained in more detail with reference to FIGS. 1-15.
  • Measuring Current Surges and Detecting a Short Circuit
  • Current surges can be created in a number of ways. Some may be part of normal operation conditions, such as starting a vehicle, while others are caused by an unsafe operating condition, such as a short circuit in the system. These surges are to be detected and measured so as to determine a current condition of an electrical system, and take favorable action, if necessary. When the current surges, there is also a large surge in the magnetic field of the buss bar 100. The Hall Effect sensors 210 a and 210 b can be used to detect this surge. The term “Hall Effect” refers to a potential difference observed between the edges of a conducting strip carrying a longitudinal current when placed in a magnetic field perpendicular to the plane of the strip, which in the present disclosure is the plane of the buss bars 100 and 400.
  • In one embodiment, each Hall Effect sensor 210 a and 210 b is placed near the edge of a conducting path of the buss bar (e.g., of 102 a or 102 b) where the magnetic field is strongest so the Hall Effect sensors can be more effective. Each Hall Effect sensor can measure the current in the conductive path. Each Hall Effect sensor then reports the current to the microcontroller 209. The microcontroller 209 can then determine whether or not a short-circuit condition exists by analyzing the magnitude and duration of the surge. If the surge satisfies the conditions for a short circuit, the microcontroller can signal the switching driver circuit 204 to activate the isolation circuitry, and therefore disconnect the battery 705 from the load 715.
  • Hall Effect sensors require a relatively large current (several mA) to function. If used continuously to monitor the current, the Hall Effect sensors 210 a and 210 b can drain the battery in a relativity short amount of time. To prevent this, a low-power consuming method, such as the op-amp-based amplifier in combination with the ADC 709 can be used as the surge detection circuit 713 (FIGS. 7 and 10). This surge detection circuit can also act as a current sensing circuit and can monitor the relative current by measuring the voltage difference across the drain and source of the electrically parallel array 304 of switches. While this method consumes very little power and can detect a surge in current, it cannot accurately measure the surge at high levels.
  • In one embodiment, the surge measuring circuit 710 remains off until the microcontroller 209 signals the microcontroller 209 to turn on, thereby saving power. When the surge detection circuit 713 detects a surge, the surge detection circuit 713 signals the microcontroller 209, which in turn directs the surge measuring circuit 710 to turn on. The microcontroller 209 can turn on the Hall Effect sensors 210 a and 210 b to measure the magnetic field, determine the current level, and report back to the microcontroller 209. The microcontroller 209 can then determine (from its programming) whether the surge constitutes a short circuit and, therefore, whether the isolation circuitry is to be activated. For example, a pre-defined threshold level of current can be set for a particularly-sized battery 705 or load 715 (or a certain combination thereof) that is compared to the determined surge in current to determine whether the surge constitutes a short circuit. In this way, the low-current consuming surge detection circuit 713 can save power by anticipating a potentially high current situation where the BMS 700 might need to turn on the Hall-effect sensors to measure the surge in current. This approach allows for constant monitoring of current levels without draining the battery 705 and can be done quickly enough to isolate the battery 705 before a short circuit can cause significant damage.
  • In many low-power current sensing circuits, a series resistor is used for current measurement by measuring the voltage across the resistor and calculating the current using ohms law. In the present BMS 700, a series resistor may not be practical because of the very large currents present. Every conductor, however, has a resistance, although in some cases the resistance is small, it could be treated as a series resistor. The resistance of such a conductor can be measured using a very accurate device because the resistance is so small, so that determining a current flow through the conductor can be performed at a proper granularity and with accuracy.
  • Accordingly, the buss bar 100 a, 100 b, 400 a or 400 b can be considered as a series resistor, and the current can be calculated by measuring the voltage across the buss bar and using ohms law. In the present BMS 700, the measurement can be done with measurement circuitry including the ADC 709, which the microcontroller 209 can use to measure an accurate voltage across the buss bar. In one embodiment, the measurement circuitry is integrated with or operatively coupled to the microcontroller 209. Because the resistance is small and slightly varied with each buss bar used as a conductor, the resistance is preferably measured in production during calibration and stored in the memory 207 or other firmware, so as to be available to the microcontroller 209 during operation. During operation, the microcontroller can determine the current flowing through the switches 302, using Ohm's Law, from the measured voltage and the stored resistance. The measurement circuitry can also include a ranging circuit to supply the ADC 709 with the correct range of voltages that corresponds to the possible current magnitudes. In one embodiment, this ranging circuit can include an op amp, voltage divider, and overvoltage protection.
  • The resistance measurement circuitry (and/or the microcontroller 209) can also be programmed to distinguish between a high current surge situation that occurs, for example, when starting a vehicle, and a high current surge caused by an actual short circuit. The resistance measurement circuitry can do this by monitoring the time at which the current surge (and a current surge of a particular threshold level) is at an expected level for starting a vehicle. When a short circuit is detected, the switching driver circuit 204 is directed to send a signal to the switch gates to turn off the switches 302 before damage can occur, and prevents the switches from being turned on until the short-circuit is removed.
  • Voltage Measurement and Low Voltage Detection
  • A lithium iron phosphate (LFP) cell or cell bank produces an output voltage of approximately 3.3 volts. This output voltage commonly has a narrow range of safe operating voltages, approximately between three (3) and four (4) volts. Operating outside of this operating voltage range will cause the cells to degrade to the point where they will no longer hold a charge and become unusable. The BMS can, therefore, detect when the voltage is outside of the optimal range and isolate the battery from being overcharged or over discharged. The voltage of each bank of cells can be monitored independently as well as the entire pack voltage collectively, to be able to pinpoint individual banks that can be overcharged or over discharged. An ADC can be used to detect voltage levels.
  • As the voltage drops while the battery 705 is being discharged, the microcontroller 209 can be programmed to recognize where the voltage is in relation to the operating range. Additionally, multiple pre-programmed or preset lockouts can be programmed to desired voltage thresholds. When the microcontroller 209 determines that one of these thresholds has been met, the microcontroller can direct the isolation circuitry to activate. The ability to program these presets is advantageous because it allows for quick and easy custom configurations for diverse applications such as use of different chemistries, automotive and marine engine starting, auxiliary power units, emergency power storage, and others. When a voltage threshold has been met, a signal can be sent to activate the isolation circuitry until a specified condition is met.
  • The most common presets can include, but not be limited to:
  • Reserve Voltage:
  • Reserve voltage is when the voltage level of the battery 705 drops to a dangerously low level but not yet outside of the safe operating range. This is set to reserve enough battery capacity to start the vehicle without dropping below the operating voltage range. The reserve voltage can be reset manually (via the reset button 228) or wirelessly, for example, by a mobile device.
  • Low Voltage Lockout:
  • A low voltage lockout can be reached when the voltage level of the battery 705 has dropped below the operating voltage. The battery can remain at this low level for long periods without degradation of the cells and this level is specific to each type of battery chemistry. The microcontroller 209 can be programmed with a low voltage lockout to allow reset only when the battery is recharged to a level within the safe operating range. The reset can happen manually through the rest button 228, a wireless signal or the like. The microcontroller 209 can also be programmed to automatically reset the battery 705 when the battery 705 is safely within the safe operating range.
  • Critical Voltage:
  • At and below a critical voltage level, the battery 705 can still be usable, but cell degradation can start to occur, reducing the operational life of the battery. This level is specific to each type of battery chemistry. The longer the battery stays below this level and the lower the voltage gets, the greater the degradation that occurs. The microcontroller 209 can track the length of time the voltage stays in this state. The microcontroller 209 can be programmed with this critical voltage and only allow reset when the battery is recharged to operating levels.
  • Temperature Monitoring of the BMS
  • A temperature sensor 234 (or thermal sensor) located near or against a buss bar 100 a, 400 a or 100 b, 400 b can be used to monitor temperature levels of the BMS. The temperature sensor relays the temperature to the microcontroller 209. In one embodiment, when a specified high temperature is reached, the microcontroller 209 can direct the switching driver circuit 204 to send a signal to the transistor-based switch gates to turn off the switches 302 before damage can occur, and prevents the switches from being turned on until the temperature has returned to a specified level within the safe operating range.
  • Temperature Monitoring of Banks of Cells
  • A thermal sensor (not shown), such as a thermistor, can be located in or around each cell pack (or bank of the battery 205) when the cell pack is manufactured. In one embodiment, the thermal sensor is located centrally in the bank as that is where heat will concentrate the most. The thermal sensor can then relay the temperature of the cell pack to the microcontroller 209, allowing the temperature of the cell pack to be monitored to determine whether the cell pack is within acceptable operating temperature ranges. When a specified high temperature is reached, the switching driver circuit 204 can send a signal to the transistor-based switch gates to switch off the switches 302 before damage can occur, and prevent the switches from being turned on until the temperature has returned to safe operating levels.
  • Current Leakage Detection
  • The BMS 700 can detect when there is a low amount of current being drawn from the battery while the engine is not running (for example, when the lights are left on, etc.). In this situation, the BMS can alert the user and even be programmed to isolate the battery so further leakage cannot occur. It can determine whether or not the engine is on by monitoring the charge current from the alternator and use this information to detect a slow steady power draw on the battery when the engine is not running.
  • Cell Bank Balancing
  • When the output voltage of the cells of a battery bank is outside of the operating range, cell degradation starts to occur. It is advantageous that each cell bank be fully charged. However, cells can charge and discharge at different rates, resulting in different charge levels in each bank. During the charging process, some cells reach full charge before others and begin to overcharge. Overcharging can start to degrade the battery cells. It is therefore advantageous during charging to detect when the voltage reaches its optimum, fully-charged level and to protect each cell bank from being overcharged or left undercharged. Cell balancing is beneficial because it prevents unbalanced cell banks that lead to overcharging of the bank and damage to cells, as well as preventing inability for the battery to be fully charged.
  • The BMS 700 can use either passive or active cell balancing. With passive cell balancing, the bank balancing circuitry 603 includes charge shunt circuitry to ensure the cells in the battery 705 are charged uniformly. When battery cells are discharged, the cells do not always discharge uniformly. This can cause an imbalance when recharged. To prevent an imbalance in charging, the cell balancing circuitry 603 can be used to redirect the current from a fully charged bank of cells to a bank of resistors that dissipate the charge to ground until all of the cell banks have reached full charge. A bank voltage sensor 703 can be used to monitor the cells of the battery 705 and a voltage divider circuit 1400 (FIG. 14) can be used to create a measurable signal for the ADC and measure the charge level of each cell bank.
  • The BMS 700 can alternatively, or additionally, have active balancing as a part of the cell balancing circuity 603. Active balancing redirects the current from a fully charged cell bank to another bank that isn't fully charged and continues doing this until all banks are fully charged. This is advantageous because the battery can be fully charged using less power and in less time.
  • Additionally, the BMS 700 has features programmed into its firmware, e.g., on the circuit board 200 and within the microcontroller 209 and other components, to provide functionality that does not exist with current starter batteries as detailed below.
  • Data Logging
  • Tracking Health Indicators:
  • Replacement of batteries is typically done either when the battery no longer holds a charge (a dead battery) or on a schedule. The health of a lead-acid battery is difficult to determine and therefore when the battery should be replaced cannot be accurately determined. A dead battery can cause considerable inconvenience and cost, especially in the trucking industry. Efforts are made, therefore, to prevent the battery from failing in the field. A schedule can be created that calls for changing the battery well before its possible end of life, regardless of how much life can be left. In most instances, there is considerable life left in the battery, but because it is indiscernible how much, the trucking industry (among other industries) prefers to remove doubt and replace the battery. This has a considerable cost that the industry has no choice but to accept. A lithium battery that includes or is managed by a BMS can be diagnosed and its operational life can be determined with a certain degree of accuracy, thereby optimizing the use of the battery. Tracked health indicators can be reported back to the user to signal when it is time to replace a battery, e.g., through the display 230.
  • Transistor-Based Switch Degradation:
  • Switching transistor-based switches 302 such as MOSFETs at high currents cause the switches to breakdown over time, although tests show these last for at least hundreds of short circuit events using the methods described in this application. When a switch in a particular subarray fails, the load decreases in that subarray. If the switches in that subarray continue to fail, the load will continue to decrease. If a switch in another subarray fails, the load balance will fluctuate. The BMS 700 can detect the breakdown (degradation) of the switches by monitoring these changes in load balances between the individual conductor paths (with the different subarrays of the buss bars) using the current sensing capability of the surge detection circuit 713 to determine current levels in each conductive path. The microcontroller 209 can receive the current levels in each conductive path and compare the two current levels. When a difference between the two current levels are beyond a pre-defined threshold amount, for example 1, 2 or 5 amps (or some other threshold), the microcontroller 209 can generate an alert indicative of a certain level of switch degradation, e.g., an audible alert or a visual alert through the display 230.
  • Battery Cell Degradation:
  • As a battery cell reaches its cycle life limit (or when it is used outside of its operating conditions), the battery cell will start to lose its ability to hold a charge. The charging holding capability of each cell bank can be monitored to detect when this degradation starts to occur or detect a level of cell degradation. Determining cell degradation in this way can be performed by one or a combination of methods, as follows:
  • (1) In one embodiment, the ADC 709 can be used to measure the cell voltage and determine the number of charge cycles the battery has experienced (which is limited) by counting the times the voltage has fluctuated from high to low and back. Beyond a certain number of charge cycles, the battery 705 begins to degrade.
  • (2) In another embodiment, the microcontroller 209 can monitor the cell banks of the battery 705 for a critical voltage level and for an amount of time spent at the critical voltage level. The critical low voltage level is a low voltage level that can be defined for banks of batteries depending on type and size of battery. The microcontroller 209 can monitor and determine a length of time a battery bank has been at critical voltage levels to detect cell degradation. The longer the battery has been kept at critical levels, the more degradation that occurs. This degradation occurs even if the battery is not being used. Understanding this information can help to determine whether the battery has been maintained properly over its life.
  • (3) The microcontroller 209 can also track a number of times the battery 705 has been charged and discharged, including how often the battery has been discharged in a normal fashion (for example in starting the vehicle) and how often the battery 705 has been deep cycled (e.g., running other things that bring the charge down further than with just a regular vehicle start). Based on this (and potentially other) information, the microcontroller 209 can determine not only if battery capacity is decreasing over time, but also whether there is a problem with the charging system (e.g., an alternator) and whether an electrical system is using more or less power than normal (e.g., lights burned out or short circuits present).
  • The microcontroller 209 can then generate an alert (such as an audible alert of a visual alert on the display 230, or a data download to a smart phone or another computer) indicative of degradation of a bank of cell in the battery 705, responsive to detecting one of the above three conditions. In this way, the BMS 700 can more accurately detect battery cell degradation and timing of battery replacement.
  • Event Logging:
  • As events such as these occur, the events can be recorded and reported back to the user to help understand how the battery is being used and how it is performing. Examples of such events include, but are not limited to: (1) short circuits; (2) high temperature levels; (3) low voltage levels; and (4) time spent at critical voltage, for example.
  • Communications & Control
  • Additional features allow for communication with and external control of the BMS 700 using either wired (such as a USB port) or wireless methods (such as Wifi, Bluetooth, GSM and other technologies that can transmit to a remote location) or a combination of both. Components for these features can be placed on the circuit board 200 or on a satellite board connectable to the circuit board 200 through the satellite board connector 214. The ability to monitor and control a vehicle battery while it is installed in the vehicle provides a powerful advantage. This ability enables the user to accurately diagnose problems as well as identify potential problems before the problems occur. When the microcontroller 209 receives signals and reports from the various methods of monitoring the battery pack as described herein, the microcontroller 209 can record that information forming a battery history and saving that history for later retrieval.
  • The BMS 700 further provides for downloading or transmission of logged data (health indicators and events, for example) from the BMS 700 to a user, who can be at a remote location through wired or wireless means as disclosed herein. Such data communication allows the tracking of battery usage history. When the battery 705 is operational, the data can be used to diagnose the health of the battery and determining the optimal time for replacement. In the case of a failed battery, the data can be used to determine the cause of the failure. And, during testing, the data can be used to see the performance of the BMS 700 and a coupled battery.
  • Updating of Firmware:
  • Before the battery system with the BMS 700 is put into service, its firmware is loaded. Also, from time to time, improvements to the firmware can be made. Loading and updating firmware can be done through a data port, such as the USB port 216 or wirelessly via the wireless circuitry 220.
  • GPS Locating Circuitry:
  • The GPS circuitry 224 allows a vehicle's location and travel routes to be tracked and monitored. This information, combined with wireless communication can allow the vehicle's location to be reported to a remote location away from the vehicle when the battery system happens to be lost, located in a stolen vehicle, or has some other need to retrieve its global coordinates.
  • User Initiated Control:
  • The BMS 700 can also provide for user-initiated isolation of the battery 705 from the system (e.g., from an electrical system or other load source) as well as user-initiated re-connection of the battery 705 to the system. In one embodiment, the user can shut down the BMS 700 to perform the isolation. For example, the user can initiate isolation manually with a reset button (e.g., the reset button 228 acting as a toggle switch or another button) or remotely with a mobile device or other remote control device. This also allows the user to shut down the engine remotely in the case, for example, the vehicle is being used without proper authorization or has a hazardous condition (e.g., is on fire) and needs to be shut down. The battery 705 may also be isolated from the system by proximity of a paired electronic or mobile device, such as a cell phone using a certain setting. Accordingly, various embodiments allow for putting the battery 705 in isolation (or taking the battery out of isolation) depending on the situation and user preference.
  • For example, a user may want to trigger isolation (or return from isolation) to perform any of the following functions:
  • (1) It is common in the trucking industry for vehicles to be stolen along with any cargo. Accordingly, the user may want to intentionally prevent the passing of high current (e.g., sufficient current to start a vehicle) by placing the BMS 700 into an anti-theft or “locked” mode, when the user is away from the vehicle or plans to leave the vehicle. The BMS 700 can go into locked mode in response to a deactivation signal or other indicator.
  • In one embodiment, the user can put the BMS 700 into locked mode through a smart phone application that communicates through the Internet and with the wireless circuitry 220, for example. Alternatively, or additionally, the microcontroller 209 can track a location of the user through the user's smart phone in comparison with the location of the vehicle (through the GPS circuitry 224), and be pre-programmed to put the BMS 700 in locked mode after the user has passed a certain distance from the vehicle. Similarly, the microcontroller 209 can bring the BMS 700 out of locked mode when the user returns within that distance of the vehicle.
  • In another embodiment, the wireless circuitry 220 includes near-field communication capability (such as Bluetooth® by the Bluetooth® special interest group) and can sense when the user leaves the vicinity of the vehicle. The microcontroller 209, operatively coupled to the wireless circuitry 220, can then detect the user has left the vehicle and be pre-programmed to place the BMS 700 into locked mode. To put the BMS 700 back into operation mode upon return to the vehicle, the wireless circuitry 220 detects that the user is back in range, and makes the BMS 700 fully operational with high current capability.
  • When in locked mode, the microcontroller 209 can detect and prevent the passing of high current. By intentionally isolating the battery from the system, the vehicle cannot be started. In locked mode, for example, the BMS 700 can allow a low specified number of amps to be drawn from the battery to allow for continuous functioning of basic appliances such as a clock, a radio, security features, and the like. In locked mode, however, the BMS 700 can detect a sudden high current surge (through a start attempt) and isolate the battery. The BMS 700 can also alert the user through one of the communication interfaces when such an event occurs. When the user returns to the vehicle, the BMS 700 can be reactivated such as discussed above, which reconnects the battery 705 to the electrical system of the vehicle. Isolation and re-connection can additionally be protected by a passcode.
  • (2) The user may want to access the reserve power in the battery 705. To do the user can provide a reset command, for example, by way of a reset button on the battery 705 or a remote reset that can be sent via a mobile application or the like, wirelessly.
  • (3) Also, if for some reason the BMS 700 has been isolated the battery 705 from the load source due to a harmful condition, and the condition has been repaired or resolved, the BMS 700 can then be reactivated. For example, the BMS 700 can be reactivated in response to sensing the proximity of a remote device, such as a mobile electronic device of the like.
  • Remote display of the BMS 700 status and other logged data may be provided to a remote device, such as on a mobile device or remotely operating computing device. A remote display has the advantage of not having to be at the battery to see its status and read data from the battery. For example, a fleet manager could obtain all the data from the batteries in the fleet at a single location, without having to go to each vehicle.
  • The status display can be as simple as an LED display 230, or other more complex display types. This allows the user to observe the status directly on the battery 705.
  • Power Savings
  • The BMS 700 may be designed to save power when not in operation. During an event, such as turning on a vehicle, powering up a load source, detecting a short circuit or a voltage or current spike, for example, the BMS 700 can be in full power mode. When full functionality of the BMS 700 is not needed, the BMS 700 can go into one of three lower power states as follows.
  • Sleep Mode:
  • The BMS 700 may spend most of the time in this mode in which the BMS is operational, but draws little current and has little energy leakage. The sleep mode may include when the Hall Effect sensors 210 a and 210 b are turned off because they are not needed, as previously explained.
  • Hibernation Mode:
  • The BMS 700 can go into hibernation mode when the current consumption from the battery 705 is reduced by a factor on the order of a hundred times. In other words, current consumption is much less than would otherwise be consumed. In one embodiment, both the Hall Effect sensors 210 a and 210 b and the microcontroller 209 are powered off during hibernation mode. Hibernation mode can be entered at times other than after detecting a critical voltage threshold. For example, after detecting a period of non-use of the battery 705 by the load source, and to preserve energy of battery 705, the BMS 700 can enter hibernation mode.
  • Low Power State:
  • The BMS 700 can enter a low power state when the microcontroller 209 powers down one or more of the auxiliary circuitry on the circuit board 200, and puts itself into an ultra-low power state. The microcontroller 209 can also be activated periodically to monitor vital signs or can be activated when an event occurs that requires the BMS 700 take action in response to the event.
  • The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present embodiments are to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description. While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the above detailed description. Accordingly, the embodiments are not to be restricted except in light of the attached claims and their equivalents.

Claims (25)

    What is claimed is:
  1. 1. An apparatus comprising:
    an isolation circuitry including multiple, transistor-based switches arranged electrically in parallel to isolate a battery from a load source, wherein the battery is capable of providing high levels of current;
    a first buss bar to which first pins of the multiple switches are connected, wherein the first buss bar is to be connected to the battery;
    a second buss bar to which second pins of the multiple switches are connected, wherein the second buss bar is to be connected to the load source; and
    a microcontroller programmed to control the multiple switches substantially simultaneously to isolate the battery from the load source upon detecting a predetermined condition.
  2. 2. The apparatus of claim 1, further comprising a heat-conducting bar made of a heat-conducting metal and thermally coupled to the multiple switches, to equalize a temperature across the multiple switches.
  3. 3. The apparatus of claim 1, further comprising:
    a switching driver circuit operatively coupled to the microcontroller and to turn on and off the multiple switches responsive to signals from the microcontroller; and
    a plurality of metal traces connecting gates of the multiple switches to the switching driver circuit that are of equal length, such that a signal from the switching driver circuit arrives at the multiple switches at substantially the same time.
  4. 4. The apparatus of claim 1, wherein the multiple switches are arranged in a first subarray and a second subarray, wherein a number of the multiple switches in the first subarray are equal to those in the second subarray.
  5. 5. The apparatus of claim 4, wherein the first buss bar and the second buss bar each include a first conductive path and a second conductive path that connect, wherein the multiple switches of the first subarray are located in a line along an edge of the first conductive path and the multiple switches of the second subarray are located in a line along an edge of the second conductive path.
  6. 6. The apparatus of claim 5, wherein a first switch in the first subarray and a first switch in the second subarray are located so as to be equidistant from the load source along, respectively, the first buss bar and the second buss bar in order to synchronize a time for current to arrive at each of the first switches.
  7. 7. The apparatus of claim 5, further comprising:
    a current measuring circuit to:
    determine a first current of the first conductive path;
    determine a second current of the second conductive path; and
    notify the microcontroller of the first current and the second current; and
    wherein the microcontroller is further to generate an alert indicative of the first current and the second current differing beyond a pre-defined threshold amount indicative of degradation of one or more of the multiple switches.
  8. 8. The apparatus of claim 1, wherein the predetermined condition comprises one of: a short circuit in the load source, overheating of the battery, overheating of the isolation circuitry, a low-voltage threshold of the battery, or a user-initiated shut off.
  9. 9. The apparatus of claim 1, further comprising a metal oxide varistor (MOV) coupled to the first buss bar or to the second buss bar in parallel with the multiple switches, to provide voltage suppression by shunting current caused by high voltages away from the multiple switches.
  10. 10. The apparatus of claim 1, further comprising:
    a printed circuit board located between the first buss bar and the second buss bar and to which is attached the microcontroller; and
    a thermal sensor attached to the printed circuit board and operatively coupled to the microcontroller, wherein the thermal sensor is to:
    measure a temperature level of the second buss bar; and
    responsive to detecting a temperature above a pre-determined threshold temperature, send a signal as an over-temperature indicator to the microcontroller; and
    wherein the microcontroller is to switch off the multiple switches responsive to the signal.
  11. 11. The apparatus of claim 1, further comprising measurement circuitry to:
    measure, to a high level of accuracy, a resistance of one buss bar selected from the first buss bar and the second buss bar;
    determine a current level through the one buss bar in view of a voltage measured across the one buss bar and the resistance of the one buss bar; and
    detect a high current surge condition in view of the current level being over a predetermined threshold high current.
  12. 12. The apparatus of claim 11, wherein the load source is a vehicle, and wherein the measurement circuitry is further to distinguish the high current surge condition in view of the current level being below the predetermined threshold high current.
  13. 13. An apparatus comprising:
    an isolation circuitry including multiple, transistor-based switches arranged electrically in parallel to isolate a battery from a load source, wherein the battery is capable of providing high levels of current of at least 400 amperes;
    a switching driver circuit operatively coupled to the isolation circuitry such as to switch off the multiple switches simultaneously; and
    a microcontroller operatively coupled to the switching driver circuit, wherein the microcontroller is to direct the switching driver circuit to turn off the multiple switches responsive to detecting a predetermined condition.
  14. 14. The apparatus of claim 13, wherein the multiple switches are arranged in a first subarray and a second subarray, wherein a number of the multiple switches in the first subarray are equal to those in the second subarray, wherein a first switch in the first subarray and a first switch in the second subarray are located so as to be equidistant from the load source.
  15. 15. The apparatus of claim 13, wherein the multiple switches operate within a range of switching rates, and wherein the switching driver circuit is to switch off the multiple switches at a slowest rate within the range of switching rates without exceeding a maximum allowable power dissipation caused by switching.
  16. 16. The apparatus of claim 13, wherein the battery includes a plurality of banks of cells, further comprising an analog-to-digital converter (ADC) to measure a voltage of a bank of the plurality of banks of cells and to send the voltage to the microcontroller, wherein the microcontroller is further to:
    determine a number of charge cycles in which the voltage has cycled between a specified first voltage and a specified second voltage;
    determine an amount of time in which the bank is at a critical voltage level that depends on a type of the battery; and
    generate an alert indicative of degradation of the bank responsive to passing a threshold number of charge cycles and a pre-defined amount of time at the critical voltage.
  17. 17. The apparatus of claim 13, wherein the predetermined condition comprises a high pre-set current level over a short period of time, wherein an amount of the high pre-set current level depends on the load source.
  18. 18. The apparatus of claim 13, wherein the predetermined condition comprises a reserve voltage below which the microcontroller is to generate an alert to reset the battery in order to access reserve capacity.
  19. 19. The apparatus of claim 13, wherein the predetermined condition comprises a low-voltage threshold below which the microcontroller is further to:
    shut off the multiple switches to protect the battery from over-discharging; and
    require charging the battery above the low-voltage threshold before accepting a reset to begin drawing on the battery again.
  20. 20. The apparatus of claim 13, wherein the microcontroller is further to:
    retrieve a critical low voltage for the battery;
    track an amount of time at which the battery is at or below the critical low voltage;
    responsive to the battery being at or below the critical low voltage for a predetermined minimum period of time, cause the battery to enter a hibernation mode of extremely low current consumption when compared with normal operation of the battery; and
    require recharging the battery above the critical low voltage before accepting a reset to again draw power from the battery.
  21. 21. The apparatus of claim 13, wherein the load source is a vehicle, and wherein the microcontroller is further to:
    restrict amperes available to the vehicle, as drawn through the multiple switches, to an amount insufficient to turn on the vehicle; and
    reverse the restriction in amperes responsive to receiving a signal indicating presence of an authorized operator.
  22. 22. An apparatus comprising:
    an isolation circuitry including multiple, transistor-based switches arranged electrically in parallel on a circuit board, wherein the isolation circuitry is to isolate a load source from a battery that is capable of providing high levels of current;
    a surge detection circuit including an operation amplifier to detect a surge in current by measuring a voltage difference between source and drain of a subset of the multiple switches;
    a surge measuring circuit to measure a magnetic field and to determine a current level of the surge in current; and
    a microcontroller operatively coupled to the surge detection circuit and the surge measuring circuit, wherein the microcontroller is to:
    receive a first signal from the surge detection circuit, wherein the first signal is indicative of detecting the surge in current;
    turn on the surge measuring circuit responsive to the first signal;
    receive the current level of the surge from the surge measuring circuit; and
    send a second signal to switch off the multiple switches responsive to determining that the current level is above a pre-defined threshold current level indicating a short circuit.
  23. 23. The apparatus of claim 22, wherein the surge measuring circuit includes a Hall Effect sensor attached to the circuit board with which to measure the magnetic field.
  24. 24. The apparatus of claim 22, wherein the surge detection circuit further includes a digital-to-analog (ADC) circuit to generate the first signal responsive to the surge detection circuit detecting the surge in current.
  25. 25. The apparatus of claim 22, wherein the microcontroller is further to set the pre-defined threshold current level according to a size of the battery or a size of the load source.
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