GB2491051A

GB2491051A - Charging system for a multi-cell power supply

Info

Publication number: GB2491051A
Application number: GB1212821.1A
Authority: GB
Inventors: Jolyon M Crane
Original assignee: PG Drives Technology Ltd
Current assignee: PG Drives Technology Ltd
Priority date: 2012-07-19
Filing date: 2012-07-19
Publication date: 2012-11-21
Also published as: GB201212821D0

Abstract

A powered system includes a charging system for a rechargeable multi-cell power supply 19 (e.g. a lithium ion rechargeable battery), the charging system comprising a monitoring arrangement 17 of one or more parameters of different cells, and a charge controller 10 to adjust the charging regime for the cells dependent on the input from the monitoring arrangement, for example using charge balancing. The charge controller is discrete from a main control system 12 of the powered system and enables disconnection of the power supply from the main control system to inhibit a motor drive of the powered system during charging of the power supply. The arrangement is particularly suitable for use with a mobility vehicle.

Description

A Cell Management System This invention relates generally to a battery management circuit, and more particularly, but not exclusively, to such a circuit capable of powering mobility vehicles.

S

Mobility vehicles, for instance medical mobility vehicles, which are currently on the market, typically use lead-acid batteries as their power source. Consequently the well established medical mobility vehicle industry uses system voltages, components and chargers that have been optimised to conform to this battery type.

Disadvantages with such systems are that the lead-acid batteries have a low energy to weight ratio compared to other types of battery that are available. It is desirable to make the battery as light as possible since in many instances the medical mobility vehicles, for instance wheelchairs and scooters, are designed to be dismantled and transported in motor vehicles to the place they will be used. There is therefore a trade off between the need to make the vehicle (consequently the battery) as light as possible and maximising the range over which the vehicle may be used.

Other battery types, for instance lithium-ion batteries, offer the potential for longer range and longer life cycles and are also lighter in weight, however they are not compatible with standard mobility vehicle components and chargers currently on the market. Further to this the nominal voltage delivered by a single lithium-ion polymer battery cell is 3.6 Volts and for a single lithium-ion phosphate cell 3.2V. Several lithium-ion battery cells would need to be stacked in series in order to provide sufficient voltage for many applications.

Rechargeable batteries are nearly all sensitive to the charging and discharging regime they experience over their operating lives. Lithium-ion cells are less sensitive to deep discharge cycles, however they have very strict maximum charging voltages and cells must be charged to their maximum voltage in order to maximise charge capacity. However, charging to a lower cell voltage and sacrificing some charge capacity enables the operating life of the cells to be significantly extended. This can be up to a factor of 2 or 4 times.

Likewise, when lithium cells are discharged, there is a minimum allowable voltage across each cell and reducing the voltage beyond this limit can reduce the capacity and increase the cell self-discharge or leakage. By raising the minimum allowed cell voltage, the operating life of the cell or battery can be extended. This is especially the case where discharge currents are high.

S

In the case where the mobility vehicles are used very infrequently, the vehicle and battery may be stored for long periods. It is undesirable to store the battery with cell voltages at or near the maximum and minimum allowed values since the battery or individual cells will deteriorate and potentially lose charge storage capacity or exhibit increased self-discharge.

Furthermore, storing cells with cell voltages at their maximum increases the risk of cell failure and fire.

It is therefore an object of the present invention to provide an improved mobility vehicle battery management circuit which alleviates the above mentioned problems and offers the versatility of powering a mobility vehicle over a longer range, or, altematively increasing the life time of the battery, depending on the application desired.

In accordance with a first aspect of the present invention, there is provided a charging system for a rechargeable multi-cell power supply for a powered system, the charging system comprising: a monitor arrangement for monitoring one or more parameters of separate cells; a charge controller arranged to adjust the charging regime for the cells dependent upon input from the monitor arrangement, such that separate cells may be subject to different charging regimes.

It is preferred that the charge controller is in communication with but discrete from a main system controller for the powered system. The powered system may be an electrically powered vehicle, or the like. The cell arrangement will typically be a rechargeable battery arrangement and aspects of the invention are particularly suited to use with lithium ion battery arrangements.

It is preferred that the cell voltage is monitored for the separate cells and the charging regime for the cells may be adjusted dependent upon cell voltage input from the monitor arrangement, such that separate cells may be subject to different charging regimes.

In certain embodiments, cell temperature may be monitored for the cells and the charging regime for the cells may be adjusted dependent upon cell temperature input from the monitor arrangement, such that separate cells may be subject to different charging regimes.

Beneficially, the charge controller is arranged to initiate a charge balancing function for the multi-cell power supply in response to the input from the monitoring arrangement.

It is preferred that, in the event of certain cells have a monitored voltage that is different (voltage mismatch) by a predetermined amount (voltage mismatch threshold) the charging regime is altered to reduce the voltage mismatch.

Beneficially, the charge balancing function may be implemented using a balancing arrangement which diverts charge away from certain cells until the voltage mismatch of the cells is reduced.

The charging controller is preferably in communication with (but discrete from) a main system controller for the powered system, and the main system controller receives charge state data from the charging controller and renders a charge state display for the user to review.

Desirably the charge controller monitors the amount of charge delivered to the multi-cell power supply. Preferably, the charge state of the multi-cell power supply is calculated by means of monitoring the number of coulombs delivered to the multi-cell power supply.

Beneficially, the charge state data concerning the amount of charge delivered to the multi-cell power supply is delivered to the main system controller for the powered system.

According to an alternative aspect, the invention provides a method of charging a rechargeable multi-cell power supply for a powered system, the method comprising: monitoring one or more parameters of separate cells; adjust the charging regime for the cells dependent upon input from the monitor arrangement, such that separate cells may be subject to different charging regimes.

According to a further aspect, the invention provides a powered system including; a charging system for a rechargeable multi-cell power supply for the powered system; a controller arrangement enabling selection between alternative modes of operation of the system; wherein the charging system is arranged to operate in different regimes dependent upon the selected mode of operation.

Beneficially, dependent upon which alternative mode of operation is selected, charging is controlled to ensure different parameter limits to be set, including one or more of: maximum permitted cell charge; minimum permitted cell charge; maximum charging voltage; minimum charging voltage.

According to a further aspect, the invention provides a method of charging a rechargeable multi-cell power supply for a powered system, the method comprising: selecting between alternative modes of operation of the powered system; and operating the charging system in different regimes dependent upon the selected mode of S operation of the powered system.

According to a further aspect, the invention provides a powered system including; a charging system for a rechargeable multi-cell power supply for the powered system; a controller arrangement enabling rendering of information concerning the level of charge of the multi-cell power supply; wherein, in charging the battery, the charging system monitors the amount of charge delivered to the multi-cell power supply and corresponding delivered charge data is directed to the controller, the level of charge information rendered being derived from the difference calculated between the delivered charge and used charge data calculated by and/or delivered to the controller.

In one embodiment, the used charge data is calculated from current flow values from known parameters of the powered system. Additionally or alternatively, the used charge data is calculated from measured current flow values.

The delivered charge data may be calculated by means of monitoring the number of coulombs delivered to the multi-cell power supply.

According to a further aspect, the present invention provides a method of rendering of information concerning the level of charge of a multi-cell power supply for a powered system; the method comprising: monitoring the amount of charge delivered to the multi-cell power supply; obtaining used charge data, calculating the difference between the delivered charge data and used charge data in order to enable rendering of the level of charge information.

S

According to a further aspect, the invention provides a charging system for a rechargeable multi-cell power supply for a powered system, the charging system comprising a charge controller discrete from the main control system of the powered system and enabling disconnection of the rechargeable multi-cell power supply from the main control system of the powered system when said power supply is to be charged.

Preferably, the arrangement includes charge balancing means for adjusting the distribution of charge within the separate cells in the power supply.

Preferably the system includes a circuit having a 3 terminal input port for connecting to a battery charger.

The invention extends further to a mobility vehicle, for instance a medical mobility vehicle, capable of implementing one or more aspects of the invention.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiment as described herein.

An embodiment of the present invention will now be described, by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of the battery management circuit.

In Figure 1 there is shown a battery management system comprising a circuit having three main components; a vehicle control system, a battery charging system and a battery balancing system.

A multi cell power supply, such as a battery cell stack 19, comprising a series of individual cells is connected to a standard vehicle control system. In this embodiment seven lithium-ion battery cells, such as lithium-polymer cells, are used. A fuse or cut out 18 is ananged in series to the battery, adjacent to the 24 V terminal. In operation the fuse protects the battery from external short circuits. The capacity of the cell stack 19 is optimised to 24 V, however this can be increased by using sets of parallel connected cells further connected in series.

The battery balancing system comprises a cell monitor and balancer circuit 17 connected to the individual cells of the battery 19. The cell monitor and balancer circuit 17 is further connected to at least one temperature sensing device that is placed in close thermal contact with at least one battery cell. A serial link 24 connects the cell monitor and balancer 17 to the charge microcontroller 10 which is used to monitor and control 17.

In operation the cell monitor and balancer 17 monitors the voltage and temperature of each cell. This data is passed to the microcontroller 10 via data link 24 which compares the values to pre-set upper and lower critical voltage limits. In the case that a cell is found to have a voltage approaching the upper or lower critical voltage, or where a cell has a comparatively high terminal voltage (voltage mismatch) that is different by a predetermined amount, the charge microcontroller 10 sends instructions to the monitor and balancer 17 to initiate the cell balancing function.

Once the cell balancing function is initiated, the charge is diverted from the cell via a discharge resistor until the balanced state is reached such that each of the cell voltages are approximately equal (for instance within 15 mY).

This cell balancing may be carried out in various ways and is dependent on system requirements, for example in the case that the battery capacity is very high, an active transfer circuit can be employed such that excess charge is moved to the other cells in the stack in a more efficient manner.

The integrity of the connections to the cells and temperature sensors are closely monitored by the cell monitor and balancer circuit 17. If a fault is detected then the charging or discharging of the battery cell stack is terminated. This is also the end result when multiple cells are found to approach the upper or lower voltage limits.

S

In operation, wherein the battery supplies power to the vehicle control system, the battery is connected to a main microcontroller 12 capable of connecting the motor drives to the battery 19 when desired. Further to this the main microcontroller 12 monitors and controls an operator interface and display 13 comprising a joystick or speed control and switches for controlling other peripheral devices such as external actuators, lighting or accessories 22. A battery capacity gauge 20 is also incorporated within the operator display and interface 13 and the two share a common serial data link 21.

System operation software and application settings are downloaded to the main microcontroller 12 at the manufacture stage. The software includes a wide range of advanced functions in addition to the basic vehicle driving functions. These advanced functions and settings are either enabled and configured during the control system manufacture or are enabled by means of a programming device 27, a PC interface (not shown) or the operator interface display.

The speed and other control commands from the operator display and interface 13 are communicated to the main controller 12 via a serial or CAN interface 25. The microcontroller reads the signal sent by the operator and generates the appropriate signals for the motor drive 15. The motor drive 15 then supplies suitable voltages to the motor.

Further motors may be used depending on the application.

Under fault conditions, the microcontroller disconnects the battery 19 from the motor driver 15 by applying the circuit isolation means 14.

The battery charging system comprises a three pole 1, 2, 3 socket, where poles 1 and 2 provide connections to the nominally 24V external battery/charging supply. Pole 3 is used to signal to the charge control electronics 10 that the charger has been connected and is connected to a timer that is configured in series with a low power regulator, itself connected to the charge microcontroller 10. The charge microcontroller is further connected to a low current switch, a high cunent switch and a charge cunent sensor. A serial interface is also configured connecting pole 3, the charge microcontroller 10 and the S main microcontroller 12.

Pole 1 of the charger interface is connected to a fuse 4 which is further connected to a high current charge control switch 7, which is controlled by charge microcontroller 10. A high current charge control switch 7 is connected to the charge current sensor and is also in series with the fuse or cutoff 18. A resistor 6 is included between the charger input terminal and the battery 19 via the charge current sensor Ii, and is in series with a low current switch 9.

By connecting a standard lead-acid battery charger to poles 1, 2 and 3, pole 3 is grounded to pole 2 and a change of state is detected by the timer 5, which enables the low power regulator 8. The regulator consequently provides a power supply for the charge microcontroller 10 and charge current sensor 11. The charge microcontroller 10 is linked to the system microcontroller 12 and transfers the signal that the charger is connected to the charger interface causing the motor drive to be inhibited.

The charge current sensor has a restricted operating range of +1-15 Amps, although this may be varied as desired.

Once power is supplied to the charge microcontroller 10 it begins to carry out its various functions which are now summarised: -Setting the initial state of switches 7 and 9 -Setting the initiation and control data formats for initialising and controlling cell monitor and balance 17 -Setting the format of the data from cell monitor and balancer 17 -Setting the maximum and minimum safe battery or cell voltages that constitute a fully charged or discharged condition -Setting the maximum and minimum battery or cell voltages that enable an extended charge/discharge cycle life -Setting the maximum allowed current through the charge current sensor 11 -Setting the balancer control function requirements and charge balance current value -Setting the charger specific protocol for controlling switches 7 and 9 -Setting the protocols, when applicable, for communicating to a smart' charger via serial interface 26 The various parameters used to effect the summarised tasks are obtained from microcontroller 12.

When the battery charging system is in operation, the charge microcontroller 10 establishes communication with the cell monitor and balancer 17 so that the cell and battery voltages and temperatures can be read at a desired frequency (2Hz). Once it is established that the cell voltages lie between a pre-programmed safe battery and cell voltage range, and the temperatures are established to be correct, the high charge current control switch 7 and the low current switch 9 are closed to initiate the flow of charging current into the battery 19.

Switches 7 and 9 are preferably of the MOSFET (Metal Oxide Semiconductor Field Effect Transistor) type in order to ensure that the switch voltage drop and losses are low.

During this process, the charging current flows through the charge current sensor 11, which is preferably a Hall effect sensor based device such as the Allegro ACS7 12.

Charge Microcontroller 10 reads the current flowing through charge current sensor 11 and the amount of current is integrated in order to calculate the total number of coulombs that have flowed into the battery 19 since the last time the vehicle control system was switched on.

The number of coulombs that have flowed into the battery is stored in the memory of charge microcontroller 10. When the vehicle control system is switched on and the charger is disconnected, microcontroller 12 reads the number of coulombs stored in microcontroller 10 and uses the number to update the battery capacity gauge level calculation. The memory associated with the charge microcontroller 10 is reset to zero ready for the next charging cycle.

S if during the charging cycle one or more cells show a higher than desired voltage compared to the others, then microcontroller 10 can instruct the cell monitor and balancer 17 to switch to the charge balancing function for the appropriate cells until a suitable charge balance is reached.

if the microconductor 10 detects that the cunent flowing either into or out of the battery 19 is too high then switches 7 and 9 are opened. A fault flag is stored in the microcontroller and this is communicated to system controller 12 and a charging fault condition is indicated to the vehicle operator either by the operator interface and display 13 when the control system is switched on, or by a separate indicator 29, e.g. comprising a series of bi-colour LEDS.

Fuse 4, located between the charge cunent sensor 11 and the branch of the circuit leading to the isolator 14, provides further protection in case of component failure permitting potentially damaging current flows.

When one or more of the cells approaches the maximum preset voltage across the terminals, indicating that the battery or cell charge is approaching the programmed maximum charged state, the switches 7 and 9 are controlled by the charge microcontroller 10. Switch 9 is opened while switch 7 is turned on and off intermittently at a low frequency. This ensures the cells are adequately balanced using a top-off' procedure.

The protocol of switches 7 and 9 may vary depending on the charger type connected to the system and are preset via the software, for instance, some lead-acid, or general purpose chargers may be rapidly connected and disconnected from the battery (typically a few hertz). Instead of pulsing the switch, the charging current could alternatively be tapered or cut back for a suitable period of time, before finally terminating.

The resistor 6, that is included between the charger input terminal and the battery 19 via the charge current sensor 11, provides a small current into the battery 19 in the event that switch 7 is open, and consequently prevents tripping or minimises the delay in providing current which is associated with some chargers. This also provides an additional top-off' or balancing means.

Whilst the charging, monitoring, balancing and coulomb counting processes are taking place, microcontroller 10 keeps the low power voltage regulator active by providing retrigger pulses to timer 5. If the charge process has been completed or the charger is disconnected, the microconductor 10 ceases to supply retrigger pulses to timer 5 and the recharge system can power down.

In the case where the vehicle control system is connected to a smart charger, microcontroller 10 may control the charging current and/or voltage via serial interface 26.

If the charger is still connected when the vehicle control system is switched on then the vehicle is prevented from moving and the condition is indicated to the operator.

When the vehicle control system is switched on and after initial system checks have been carried out, main microcontroller 12 determines the number of coulombs from the charge microcontroller 10 and resets the value to zero ready for the next charging cycle.

Microcontroller 12 then requests the charge microcontroller 10 to establish communications with cell monitor and balancer 17 in order to obtain the voltage status and battery temperature. These quantities are then monitored by the microcontroller 12 at a predetermined frequency (2Hz) via microcontroller 10, cell monitor 18 and serial link 24.

When the vehicle control system is switched on and the operator inputs the vehicle driving command, the microcontroller 12 closes the circuit isolator 14 connecting the motor drive 15. The motor is driven by the motor drive 15 under the command of microcontroller 12.

The speed and torque of the traction motors are controlled by Pulse Width Modulators (PWM) whereby the full battery voltage is applied to the motor for a short period of time at a fixed frequency (20kHz). The motor speed and torque is adjusted by varying the ratio of the time the battery voltage is applied to the time the battery voltage is switched off.

For example, if the battery voltage is 24V and a switching frequency is 20kHz and the period over which the battery voltage is applied to the motor is 10ps and the period when the battery voltage is switched off is 40is then the PWM ratio is 20% and the effective driving voltage is 4.8V The battery current flowing when driving the traction motor can be calculated by Ibatt=Imotor x PWM ratio. Calculating the current in this way prevents the need to use expensive high current sensors with a wide dynamic range.

In a further embodiment where multiple motors are present, then the total battery current is the sum of the resultant battery currents for each motor.

The vehicle is braked by making the at least one motor 16 act as a generator. In such cases energy is recovered by the motor drive 15, and subsequently generates a battery charging current. Microcontroller 12 is used to count the coulombs flowing out of (used charge) and into (delivered charge) the battery cell stack and together with the battery cell stack or cell temperature readings communicated via charge microcontroller 10, Cell monitor and balancer 17 and serial link 24 is able to continuously update the battery cell stack capacity gauge by calculating the difference between the delivered charge and the used charge.

At periodic intervals (typically 0.2Hz) during motor drive and standby conditions, main microcontroller 12 obtains the actual cell and battery voltages via charge microcontroller 10, general data link 24 and cell monitor and balance 17. It is then able to ascertain a refined value of the battery capacity through pre-programmed calculations stored in main microcontroller 12.

The refined battery capacity is displayed via a gauge, but could be presented by any means able to communicate a proportion of the charge remaining, for example, via LCD display.

Additionally, the calculated battery capacity is also displayed in ampere hours (Ah) wherein the battery temperature is compensated for. The number of shallow (e.g. 20% DOD) and deep (e.g. 80% DOD) cycles are also stored and displayed.

The external actuator, lighting or accessories 22 are connected via serial data and power S cable 23. If these external functions are used only for a short period of time, then they use only a small amount of power. However, in instances where the power used by them is significant with regard to battery capacity, then the main microcontroller 12 will estimate the coulombs consumed and will adjust the battery capacity gauge accordingly.

Alternatively, the accessory or function attached could feed current consumption data back to microcontroller 12 via the serial data and power cable 23 for incorporation into the battery capacity calculations.

The control system 12 and User Interface 13 offers the operator the option to optimise the battery management for maximum range or, alternatively, extending charge and discharge cycle life.

If the operator or application requires a long cycle life then this function is selected and the maximum charging voltage across each cell or battery is reduced and the minimum discharge voltage across each cell or battery is raised. The battery capacity gauge 20 is adjusted to display zero or empty when the lower allowable cell or battery voltage is reached and maximum or full when the maximum allowable cell or battery voltage is reached. In this instance, the battery capacity may be reduced by 20%.

If the operator or application requires the maximum duration of range, then this function is selected and the maximum charging voltage across each cell or battery is raised and the minimum discharge voltage across each cell or battery is reduced. The battery capacity gauge 20 is adjusted to display zero or empty when the lower allowable cell or battery voltage is reached and maximum or full when the maximum allowable cell or battery voltage is reached. Alternatively, a maximum permitted cell charge or minimum permitted call charge could be used to define the thresholds.

The battery storage and transportation function is initialised by selecting the function by means of the operator interface and display 13 or programming device 28. This then overrides the instruction to the operator to connect the battery charger as the battery is discharged and approaches the low charged state i.e. the lower allowable cell or battery S voltage.

When the battery 19 has a higher charge than that required for storage, then the cell balancer is switched on providing a load across all the battery cells. The discharge rate may be increased by connecting a load dump device across the charger input terminals.

This is particularly useful in instances where the cell balancer discharge current is small.

The load dump device consists of a resistor that draws an acceptable current from the charger socket whilst dissipating the heat generated. On initiation of the battery storage and transportation function, switches 7 and 9 are closed and the charging or discharging current is measured (or in the case of the balancer current a value is assumed). The total number of coulombs flowing into or out of the battery is calculated and stored by microcontroller 10.

While the battery storage and transportation process is activated the main control system is switched off or self shut down is effected in order to reduce the total system drain to as near zero as possible. During this time the status indicator and/or the operator interface and display show that the storage and transportation process is underway. Once the battery cells have reached the desired voltage level, microcontroller 10 opens switches 7 and 9 and timer 5 ceases to be retriggered so that voltage regulation 8 switches off The whole system is powered down ready for the vehicle to be stored or dismounted for transport.

When the vehicle control system is next switched on, the microcontroller 12 reads the number of coulombs that have been stored in microcontroller 10 in order to update the battery capacity gauge level calculation and resets the stored value to zero ready for the next charging cycle. The vehicle operator is then instructed to fully recharge the batteries.

This procedure limits significant capacity gauge errors after long periods of storage.

The microcontroller 12 is further programmed to interface to a range of batteries that have differing chemistries, storing capacities and temperature differences. The model parameters are preset for particular battery types enabling the selection of the appropriate type and the subsequent retrieval of relevant battery parameters by charge microcontroller 10 and main microcontroller 12. Programming device 27 also permits additional battery types and models to be downloaded if required and a custom battery function is available to allow individual battery and model parameters to be programmed (although this is restricted to manufacturers and distributers). The programming device 27 is capable of updating battery library models via a PC and an internet connection.

The main microcontroller 12 is programmed for optimum operating voltage and temperature ranges, and a capacity value expressed in ampere-hours (Ah) is programmed to provide a starting point for the battery capacity gauge calculations.

Following installation of a new battery, a full charging cycle is required in order to maximise initial battery gauge accuracy. Alternatively, the battery may be pre-charged externally to the vehicle in order that a full charge is available immediately. In this case, the operator will select a function that allows for a fully charged battery to be installed. In such instances, the ampere-hours capacity and the battery type (if a model is pre-stored) must be provided by the operator.

This could be developed further when a small number of batteries are used in rotation whereby a function stores the profile and therefore, the learned Ah capacity of the batteries and the battery in use can be selected so that a more accurate battery capacity gauge calculation and presentation may be made.

The battery gauge algorithm may utilise existing algorithms and may be based not only upon cell and overall battery voltages and temperatures, but also may be used in combination with impedances, by means of a Kalman filter cell or battery, so that an effective model of the battery may be continuously updated.

Where the system described is implemented in such a way as to be added onto an existing vehicle control topology, those skilled in the art would readily combine the elements within microcontrollers 10 and 12 into one single higher functionality microcontroller.

S Advantages include that the battery management system allows for lithium-ion battery arrangements (or arrangements using other battery types with similarly desirable properties) to be used in mobility vehicles thereby offering a light weight power supply having a longer duration and prolonged cycle life. Further to this, the system offers the client versatility in terms of the vehicles application and components (e.g. battery type or accessories). The purchase cost has been minimised by eliminating the need for a high current meter, and the safety of the vehicle has been maintained by adding a battery storage and transportation function and a cell balancing function. The battery management circuit further enables the lithium-ion battery arrangement (or arrangement using other battery types with similarly desirable properties) to be charged by means of standard chargers in the industry which minimises the cost of maintaining the mobility vehicles.

It should be noted that the above-mentioned embodiment illustrates rather than limits the invention, and that those skilled in the art will be capable of designing many altemative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

Claims: 1. A charging system for a rechargeable multi-cell power supply for a powered system, the charging system comprising a charge controller discrete from the main control system of the powered system and enabling disconnection of the rechargeable multi-cell power supply from the main control system of the powered system when said power supply is to be charged.
2. A charging system according to claim 1, including charge balancing means for adjusting the distribution of charge within the separate cells in the power supply.
3. A powered system including a charging system according to any of claims 1 to 2.