GB2493694A

GB2493694A - DC power supply comprising switch gear enabling parallel or series connection of batteries

Info

Publication number: GB2493694A
Application number: GB1111118.4A
Authority: GB
Inventors: Andrew George Bond
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-06-30
Filing date: 2011-06-30
Publication date: 2013-02-20
Also published as: GB201111118D0

Abstract

A power supply comprising a DC input 46, a plurality of batteries 22, a DC output 54 and switch gear for operatively connecting the DC input 46, to the plurality of the batteries 22 in parallel; or for operatively connecting the DC input 46 to the plurality of the batteries 22 in series to the DC output 46. The DC input preferably comprises a 12V DC power supply, such as four 12V batteries connectable in parallel to a 12V DC input and in series to a 48V DC output. Alternatively the batteries may comprise a first plurality of batteries connected in series, and connected in parallel with a second plurality of batteries connected in series. Similarly the first plurality of batteries may be connected in parallel, but connected in series with a second plurality of batteries connected in parallel. The power supply may further comprise a means for detecting the voltage at the DC input and for detecting the demand or load at the DC output. The switch gear may comprise electromechanical switches, such as relays 52, which may be controlled by a PLC (programmable logic controller). The invention may be suitable for use in conjunction with a fluid compressor (figure 1) such as an air compressor (16, figure 1) for inflating vehicle tyres.

Description

SWITCH GEAR

Description:

This invention relates to switch gear and in particular, but without limitation to switch gear for batteries. The invention may also relate to means for powering portable, battery-powered devices, such as air compressors.

Many devices nowadays are battery powered for reasons of convenience and portability.

For example, the use of battery-powered hand tools on building sites has virtually superseded mains-powered tools, meaning that health and safety issues that previously existed regarding the use of on-site generators, the installation of temporary mains power systems, the use of mains power in wet areas and the trip hazards that are associated with loose cabling, etc. have been greatly reduced.

However, powering a device using a battery necessarily places restrictions on the way the battery-powered device can be used. Firstly, the voltage and capacity of the battery are generally limited by the size and weight of the battery and although battery technology has moved on considerably in recent years, the implications of battery size and weight are often critical factors, especially with portable and/or hand-held devices.

Furthermore, batteries for portable devices need to be recharged at intervals, which normally requires access to a mains power supply, which effectively restricts the "range2' of battery-powered devices to the distance between available mains power points.

Attempts have been made to use alternative, readily-available, power sources for recharging batteries, such as a 12V outlet of a motor vehicle, but since the charging voltage of a battery needs to be greater than the battery's nominal voltage, vehicle-rechargeable batteries are commonly restricted to 12V systems, which often lack the power and capacity needed for heavier duty devices, such as drills, air compressors, hoists etc. It is possible, and indeed known, to retrofit a vehicle with a supplementary alternator which can provide a higher voltage output, e.g. 24V, 48V, but this necessarily involves modifying the vehicle, which can invalidate its warranty. Moreover, higher than 12V devices can only be used with vehicles that have been upgraded with a higher than 12V power supply, which restricts their use considerably.

An alternative solution also involves using a rotary take off from a vehicle's drivetrain to operate a generator and/or the device (e.g. an air compressor) directly. This solution is also largely unsatisfactory because of the capital investment involved and the fact that the device's life is intimately ties to the vehicle's life and vice-versa.

A further known solution is to provide a vehicle with a DC-DC converter that steps-up the vehicle's 12V supply to a higher voltage. However, DC-DC converters are generally expensive and fault-prone due to the high powers delivered through their solid-state circuitry. As such, the uptake of DC-DC converters has been quite limited.

A need therefore arises for an alternative means of providing a higher than 12V power supply on a vehicle.

According to a first aspect of the invention, there is provided a power supply comprising a DC input, a plurality of batteries, a DC output and switch gear for operatively connecting: the DC input to a plurality of the batteries in parallel; or for operatively connecting a plurality of the batteries in series to the DC output.

The invention therefore enables a DC voltage input to be stepped-up using a bank of batteries. In one example, the DC input comprises a 12V DC power supply, which is operatively connectable to charge pair of 12V batteries in parallel. When the batteries are needed for use, the 12V DC power supply is disconnected from the batteries and the batteries are connected in series to provide a 24V DC output.

Any number of batteries may be employed to provide different voltage outputs, e.g. three 12V batteries to provide a 36V output, four 12V batteries to provide a 48V output, etc. In addition, the batteries may be connected in series and in parallel to the DC output to provide a longer duty cycle. e.g. two 12V batteries connected in parallel to one another, which are connected in series to another 12V batteries connected in parallel to one another: the result being a 24V output available for a longer duration.

The power supply preferably comprises means for detecting a voltage at the DC input and optionally for connecting the DC input to the batteries upon detection of such a voltage. The power supply preferably also comprises means for detecting a demand, or load, at the DC output and optionally for connecting the DC output to the batteries upon detection of such a demand or load.

Demand for power may be signalled by a circuit or switch.

Since the switch gear is configured to connect the input to the batteries or the batteries to the output (in the alternative), connection of the batteries to the input and the output simultaneously is prohibited. In addition, the switch gear preferably comprises means for introducing a finite delay between the connection of the batteries to the input and output to accommodate switching delays and/or power spikes.

The switch gear preferably comprises a Programmable Logic Controller (PLC) adapted to effect switching of electromechanical switches, such as relays. The relays, where provided, may be mechanical relays, solid-state relays or a combination of mechanical and solid-state relays.

Advantageously, the invention can be implemented using relatively unsophisticated, "off-the-shelf" components (compared to a dedicated microcircuit or a DC-DC converter), which may reduce its cost and complexity, improve its longevity and/or facilitate its serviceability.

One particular application of the invention is in conjunction with an air compressor.

Breakdown and recovery vehicles are often required to attend vehicles that have punctures. Quite often, however, the attended vehicle's spare tyre is flat and needs to be re-inflated before it is safe to drive. An air compressor is therefore needed on board the breakdown and recovery vehicle to enable a flat tyre to be re-inflated. In the case of a car or small van, a simple 12V air compressor, or bottled, pressurised gas, can be used to re-inflate the tyre. However, for larger vehicles, such as lorries and trucks, a much higher inflation pressure is needed owing to the higher required air pressure within the tyre being re-inflated (the inflation pressure needs to be much greater than the nominal pressure within the tyre to ensure that air flows into the tyre).

Air compressors are inherently inefficient, and their inefficiencies increase proportionally with air pressure due to the mechanical losses inherent in air compressor design. As such, it is generally required to use an air compressor having a much higher nominal output than is required to ensure efficient operation. As such, conventional 12V portable air compressors are rarely suitable for use in re-inflating HGV tyres and a need therefore arises for a higher voltage/power air compressor of the types described in the introduction.

However, the power supply of the invention enables a higher than 12V DC air compressor to be used in conjunction with an un-modified breakdown and recovery vehicle.

According to a second aspect of the invention, there is provided a portable fluid compressor comprising: a power connector connectable, in use, to a 12V DC supply; a plurality of batteries; switch gear cooperatively connecting the 12 DC supply to the batteries or the batteries to a DC motor having a nominal operating voltage exceeding 12V; and a fluid pump operatively connected to the motor, wherein the switch gear either operatively connects the 12V DC supply to the batteries in parallel, or operatively connects the batteries to the motor in series.

The portable fluid compressor is preferably a portable air compressor having an air pump.

The fluid/air compressor may additionally comprise a pressure vessel connected to an output of the pump for storing a quantity of pressurised fluid/air. Valve means is also provided on an outlet of the pump or pressure vessel to enable the controlled delivery of pressurised fluid/air.

Any number of batteries may be employed to provide different voltage outputs. However, the motor is preferably a 48V DC motor and four 12V batteries are preferably provided for powering it.

The power connector preferably comprises an "Anderson" plug or socket for connection to a corresponding "Anderson" plug or socket commonly found in commercial vehicles. The use of a standardised plug enables the portable air compressor to be easily shared and/or transferred between vehicles.

The power supply preferably comprises a sensor for detecting a voltage at the DC input and optionally for connecting the DC input to the batteries upon detection of such a voltage. A programmable battery charger is preferably interposed between the power supply and the batteries to enable an appropriate charging profile for the batteries to be employed, e.g. a combination of trickle-and rapid-charging.

The power supply preferably also comprises means for detecting a demand, or load, at the DC output and optionally for connecting the DC output to the batteries upon detection of such a demand or load. Demand for power may be signalled by a circuit or switch. In the context of an air compressor, the demand may be signalled by a detected drop in pressure within the pressure vessel, in which case an electronic air pressure sensor could be used. Additionally or alternatively, the portable air compressor could be fitted with a manually-operated switch to switch it between a "sleep" mode in which the batteries are charged, and an "active mode", in which the batteries are connected to the motor.

The portable air compressor preferably comprises a Programmable Logic Controller (PLC) as previously described. A user control panel may be provided for selecting between different modes of operation and/or for re-programming PLC.

Preferred embodiments of the invention shall now be described, by way of example only, with reference the accompanying drawings in which: Figure 1 is a schematic perspective view of an air compressor in accordance with the invention; Figure 2 is a schematic circuit diagram showing the switching arrangement of the switch gear of the air compressor; and Figure 3 is a schematic circuit diagram of the power supply and controller therefor of the invention.

In Figure 1, an electric air compressor 10 comprises a generally cuboid framework 12 for supporting a 48V DC motor 14, an air pump 16, a pressure vessel 18, a switch gear housing 20 and four 12V DC gel batteries 22. The air compressor 10 is depicted without its outer housing, which comprises a number of sheet metal pieces bolted to the exterior of the frame 12, for reasons of clarity.

In use, the air compressor 10 is powered by connecting it to an Anderson plug-type socket (not shown) installed in a vehicle (not shown), which provides a 12V DC output from the vehicle's alternator. The air compressor 10 is connected to the vehicle's Anderson plug socket using a flexible fly-lead 24, which has a matching Anderson plug-type connector on its free end.

The fly-lead 24 provides power to the switch gear 60 located within the switch gear housing 20. When the air compressor 10 is set to "sleep" mode, by depressing a first button 26 on the exterior of the switch gear housing 20, power flows from the fly-lead 24, via the switch gear 60 and into the batteries 22. In sleep mode, the switch gear 60 provides a 12V charging voltage to each of the batteries 22 by connecting them in parallel to the fly-lead 24 via an internal charger, which regulates the delivery of DC current in a manner appropriate to the battery type (e.g. a trickle/rapid charge profile).

Meanwhile, a pressure transducer 28 monitors the air pressure within the pressure vessel 18 to ensure that it remains above a predetermined threshold. If the air pressure drops below the predetermined threshold, the transducer 28 signals for the pump 16 to kick-in, thereby re-pressurising the air within the vessel 18. When the transducer 28 "demands" a top-up, the switch gear disconnects the four batteries 22 from the charging circuit and then re-connects them, in series, to a motor controller 62 to drive the 48V motor 14. The motor 14 is operatively connected to the air pump 16 using a belt-and-pulley drive mechanism 30 (although other means may be used). The pump's exhaust 32 is connected to an inlet 34 of the pressure vessel 18 via a high-pressure air hose 36 and a check valve (not shown), which prevents air from flowing back towards the pump 16 when the pump 16 is switched off.

When the air pressure within the pressure vessel reaches the predetermined threshold, the transducer 28 signals the switch gear 60 to stop the motor 14, whereupon the motor controller 62 is switched to an "off" state, Shortly thereafter, the switch gear 60 checks that there is a sufficient voltage at the fly-lead 24, and if so, disconnects the batteries 22 from the motor controller and re-S connects them, in parallel, to the charging circuit.

In use, an operator can use the pressurised air contained within the pressure vessel, e.g. to re-inflate a flat tyre, using a second high-pressure air hose 38 connected, via a valve 40, to an outlet of the pressure vessel 18. If the operator uses enough air that the air pressure within the pressure vessel 18 drops below the predetermined threshold, then the process of topping-up the air pressure, as described above, will recommence.

Whilst in "sleep" mode, the air compressor works to maintain the batteries in as fully a charged state as possible, whilst maintaining the air pressure within the pressure vessel above the predetermined threshold.

In an "active" mode, signalled by pressing another button on the switch gear controller 20, the air compressor 10 prioritises maintaining the air pressure in the pressure vessel 18 above the threshold at the expense of the charge level of the batteries 22. Active mode may be selected where, for example, a large volume of compressed air is needed quickly, e.g. when re-inflating a completely flat I-IGV tyre.

Since not every application requires a high air pressure to be maintained within the pressure vessel 18, the switch gear provides push buttons for selecting a number of pressure thresholds to be maintained. In the illustrated embodiment, two buttons 42, 44 are provided for selecting a "normal" and a "high" pressure threshold setting, respectively. These are conveniently indicated by "down-" and "up-arrow" shaped buttons.

The electrical connections of the batteries 22 to the power supply are shown schematically in Figure 2 in which a 12V DC supply voltage is applied to input terminals 46. In charging mode, relays 48 are closed to allow DC current to flow from the input terminals 46 to each of the battery's terminals 22, in parallel, using power cables 50. When a "demand" is sensed, the relays 48 open thereby disconnecting the batteries 22 from the power supply terminals 46, and a second set of relays 52 close to connect the positive terminal of one battery to the negative terminal of a second battery, thereby daisy-chaining the batteries in series. Power output cables 54 connect the positive terminal of the first battery in the chain and the negative terminal of the last battery in the chain to a power outlet, in this case, the motor controller 62.

The switch gear 60 is shown in greater detail in Figure 3 of the drawings and comprises input power terminals 46, which are connected to a 12V DC power supply, for example, using an Anderson-type fly-lead 24 as shown in Figure 1. The input terminals 46 provide 12V DC power to a PLC 64, which is programmed to control the operation of the relays in response to button presses and transducer outputs as previously described. The input terminals 46 are also connected to a bank of mechanical relays 48 which connect/disconnect the input terminals 46 to each of the terminals of the bank of batteries 22. A separate mechanical relay is provided for each battery terminal, so in the present case, there are eight relays 48: one for each terminal of each of the four batteries 22.

The mechanical relays are powered using the 12V input terminals and are controlled using control cables 66 connecting each of the relays 48 to output terminals 68 of the PLC 64. As such, the PLC 64 can connect the batteries 22 to the input terminals to charge them in parallel or disconnect them completely using the relays 48.

when the batteries 22 have been isolated from the input terminals 46, they can be connected in series in the manner described above with reference to Figure 2. In this case, a second bank of solid state relays 52 can be used to connect the batteries in series, thereby providing a 48V DC power supply to the motor controller 62, which in turn drives the motor 14. Again, the solid-state relays 52 are powered by the 12V DC input terminals and are switched using control terminals 70 of the PLC 64.

The PLC 64 additionally comprises input/control terminals to which the operator buttons (not shown) and pressure transducer 28 are connected. The PLC is a logic controller, so can switch the various relays in response to step-change voltages corresponding to button presses, or can interpolate a variable input voltage to effect switching. In the present case, the pressure transducer outputs a DC voltage that is linearly proportional to the air pressure within the pressure vessel 18.

Hence, the PLC 64 can determine its switching by interpolating the transducer's voltage against a look-up table or pre-set thresholds that have been programmed into it.

The invention is not restricted to the details of the foregoing embodiments. For example, whilst the invention has been described in relation to a 48V DC air compressor) any voltage output could be derivable using a bank of batteries. Moreover, whilst the invention has been described in relation to a 12V supply system other voltages could equally be used, e.g. the 6V DC supply of a motorcycle alternator, the 24V DC supply of certain marine alternators, etc. The batteries could also be different types, such as lead-acid batteries, Nickel-metal-hydride, gel batteries etc. In addition, the invention could be used in the hydraulics, water and oil industries, e.g. for providing a power source (or power pack) for powering a portable hydraulic, water or oil pump, 15 respectively. As such, references herein to air compressors, air pumps, air and pressurised air etc. could equally be replaced by equivalent terminology referring to fluids in general, in particular water, oil and hydraulic fluids.

Additionally, the invention could be used to provide a portable power source for other electrical devices, for example, a crane, hoist, lighting rig, tail lift etc. installed on, or affixable to, a vehicle.

Claims

<claim-text>Claims: 1. A power supply comprising a DC input, a plurality of batteries, a DC output, and switch gear for operatively connecting: the DC input to a plurality of the batteries in parallel; or for operatively connecting a plurality of the batteries in series to the DC output.</claim-text> <claim-text>2. A power supply as claimed in claim 1, wherein the DC input comprises a 12V DC power supply.</claim-text> <claim-text>3. A power supply as claimed in claim 1 or claim 2 comprising a first plurality of batteries connected in series, the first plurality of batteries being connected, in parallel, to a second plurality of batteries connected in series.</claim-text> <claim-text>4. A power supply as claimed in claim 1 or claim 2 comprising a first plurality of batteries connected in parallel, the first plurality of batteries being connected, in series, to a second plurality of batteries connected in parallel.</claim-text> <claim-text>5. A power supply as claimed in claim 1 or claim 2, comprising four 12V batteries connectable in parallel to a 12V DC input and in series to a 4W DC output.</claim-text> <claim-text>6. A power supply as claimed in any preceding claim, further comprising means for detecting a voltage at the DC input.</claim-text> <claim-text>7. A power supply as claimed in claim 6, further comprising means for connecting the DC input, in parallel, to the batteries upon detection the voltage.</claim-text> <claim-text>8. A power supply as claimed in claim 7, wherein the means for connecting the DC input, in parallel, to the batteries comprises a relay for connecting the positive terminal of each of the batteries to a positive terminal of the DC input and a relay for connecting the negative terminal of each of the batteries to a negative terminal of the DC input.</claim-text> <claim-text>9. A power supply as claimed in any preceding claim, further comprising means for detecting a demand, or load, at the DC output.</claim-text> <claim-text>10. A power supply as claimed in claim 9, further comprising means for connecting the DC output, in series, to the batteries upon detection of the demand or load.</claim-text> <claim-text>11. A power supply as claimed in claim 10, wherein the means for connecting the DC output to the batteries upon detection of the demand or load comprises a relay interposed between the positive terminal of a first battery and a negative terminal of a second battery, and output cables connecting the negative terminal of the first battery and the positive terminal of the second battery to DC output.</claim-text> <claim-text>12. A power supply as claimed in claim 8 or claim 11, wherein separate relay is provided for each battery terminal.</claim-text> <claim-text>13. A power supply as claimed in any preceding claim, further comprising means for introducing a finite delay between the connection of the batteries to the DC input and the connection of the batteries to the DC output, or vice-versa.</claim-text> <claim-text>14. A power supply as claimed in any preceding claim, wherein the switch gear comprises a Programmable Logic Controller.</claim-text> <claim-text>15. A power supply as claimed in any preceding claim, wherein the switch gear comprises electromechanical switches.</claim-text> <claim-text>16. A power supply as claimed in claim 15, wherein the electromechanical switches comprise relays.</claim-text> <claim-text>17. A power supply as claimed in claim 15 or claim 16, when dependent on claim 14, wherein the PLC is adapted to effect switching of the electromechanical switches.</claim-text> <claim-text>18. A power supply as claimed in any of claims 14 to 17, further comprising a control panel for selecting between different modes of operation and/or for re-programming the PLC.</claim-text> <claim-text>19. A power supply according to any preceding claim, wherein the DC input is connectable to a 12V DC power supply via an Anderson-type plug or socket.</claim-text> <claim-text>20. A power supply as claimed in any preceding claim, further comprising a battery charger circuit interposed between the DC input and each of the batteries.</claim-text> <claim-text>21. A fluid compressor comprising a power supply according to any preceding claim.</claim-text> <claim-text>22. A fluid pump or compressor according to claim 21, wherein the fluid compressor comprises any one or more of the group comprising: an air compressor, a hydraulic pump, an oil pump and a water pump.</claim-text> <claim-text>23. A fluid pump or compressor according to claim 21 or claim 22, further comprising any one or more of the group comprising: a pressure vessel; a fluid pump; an air pump; valve means; a motor; an air pump; and an air a fluid pressure transducer.</claim-text> <claim-text>24. A fluid pump or compressor as claimed in claim 23, wherein the fluid pressure transducer is adapted to monitor the air pressure within the pressure vessel.</claim-text> <claim-text>25. A fluid pump or compressor as claimed in claim 24, wherein the fluid pressure transducer is operatively connected to the PLC.</claim-text> <claim-text>26. A fluid pump or compressor as claimed in claim 25, wherein the PLC is programmed to cause the pump to top-up the fluid pressure within the pressure vessel when the sensed fluid pressure drops below a first predetermined pressure threshold.</claim-text> <claim-text>27. A fluid pump or compressor as claimed in claim 25, wherein the PLC is programmed to cause the pump to stop when the sensed fluid pressure rises above a second predetermined pressure threshold.</claim-text> <claim-text>28. A fluid pump or compressor as claimed in any of claims 24 to 27, wherein the PLC is programmable to operate in: a first mode, which works to maintain the batteries in as fully a charged state as possible, whilst maintaining the fluid pressure within the pressure vessel above the second predetermined threshold; and a second mode in which the fluid pump or air compressor prioritises maintaining the fluid pressure in the pressure vessel above the second threshold at the expense of maintaining the charge level of the batteries.</claim-text> <claim-text>29. A fluid pump or compressor as claimed in any of claims 23to 28, further comprising a check valve interposed between the fluid pump and the pressure vessel.</claim-text> <claim-text>30. A fluid pump or compressor as claimed in any of claims 23 to 29, further comprising a motor controller interposed between the DC output and the motor.</claim-text> <claim-text>31. An air compressor comprising: a power connector connectable, in use, to a 12V DC supply; a plurality of batteries; switch gear cooperatively connecting the 12 DC supply to the batteries or the batteries to a DC motor having a nominal operating voltage exceeding 12V; and an air pump operatively connected to the motor, wherein the switch gear either operatively connects the 12V DC supply to the batteries in parallel, or operatively connects the batteries to the motor in series.</claim-text> <claim-text>32. A vehicle comprising a power supply according to any of claims ito 20 and an electrical device powered by the power supply, the electrical device being any one or more of the group comprising: an air compressor; a fluid compressor; a hydraulic pump; an light; a crane; a hoist; and a tail lift.</claim-text> <claim-text>33. A power supply, fluid pump or fluid compressor substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.</claim-text>