GB2206752A

GB2206752A - Rechargeable electric power unit arrangements

Info

Publication number: GB2206752A
Application number: GB08814007A
Authority: GB
Inventors: William Charles Coombes
Original assignee: JACKSON BROTHERS
Current assignee: JACKSON BROTHERS
Priority date: 1987-06-16
Filing date: 1988-06-14
Publication date: 1989-01-11
Anticipated expiration: 2008-06-14
Also published as: GB8713971D0; GB8814007D0; GB2206752B

Abstract

An over discharge protection circuit, (Figure 1), has a comparator (27) which turns off a transisitor (37), thereby turning off a relay (26) to disconnect the load, when the battery voltage falls below a reference. The circuit may be located with the battery (10) in a housing having a carrying handle, output and charging-input sockets, and means (15) to indicate that the battery is being charged. A battery charger has a regulator 54 which maintains the charging voltage at a level set by a potentiometer 52 in a potential divider circuit 51, 52, 57. In response to charging current falling below a level set by a potentiometer 64, a comparator 62 turns on a green LED 71, turns off a red LED 74 and turns on a transistor 75 which connects a variable resistor 76 into the potential divider circuit, whereby the regulator 54 then maintains the charging voltage at a trickle charge level. <IMAGE>

Description

RECHARGEABLE ELECTRIC POWER UNIT ARRANGEMENTS DESCRIPTION The invention relates to rechargeable electric power unit arrangements, and more specifically to a battery discharge protection device, to a rechargeable electric power pack unit incorporating such a protection device, and to a charging unit suitable for charging a rechargeable electric power pack unit.

Rechargeable electric power pack units find a variety of applications where mains electricity is not available, or as standby units in the case of mains supply failure. It is important that such units be properly used and properly recharged if they are to have a reasonable working life. The invention is accordingly concerned with the provision of means for avoiding damage to such units resulting from inadequately supervised use and means for conveniently and correctly charging and recharging them, without constant monitoring.

The invention accordingly provides a protection or monitoring device for protecting a battery, or battery stack, against being over-discharged. The invention can thus provide such a protection device Which. is arranged to discontinue the supply of power from the battery in response to a fall in the battery voltage to a predetermined level. The invention can also provide such a device comprising circuitry in which the battery voltage is compared with a reference voltage to provide an output when the battery voltage falls to a predetermined minimum, which output can be employed for a display and/or control function, such as to interrupt the supply of power from. the battery.

The invention can also provide a rechargeable power pack unit comprising a battery and such a protection device, the protection-device being arranged to prevent over-discharge of the battery by interrupting a connection between the battery and an output terminal of the unit when the battery has been discharged to a predetermined extent.

Conveniently, the battery voltage is compared in a comparator with a reference voltage itself derived from the battery voltage, and the comparator output is employed to cause a transistor to energise or deenergise a relay, the contacts of which are located between the battery and the output terminal.

The invention also provides a charging unit for charging and recharging a'battery, which battery may but need not be associated with a protection device in accordance with the invention, the charging device comprising means responsive to the battery charge to reduce the charging voltage from a charging or "boost" level to a maintenance or "float" level when the battery has been sufficiently charged.

The charging unit of the invention can thus operate by sensing the current flow into the battery as a voltage, comparing this voltage with a preset voltage and employing the result of the comparison to effect the desired change in output voltage, as by switching in or out a resistor, for example by turning a transistor on or off.

The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of a rechargeable power pack unit including a voltage monitoring or protection circuit, in accordance with the invention; and Figure 2 is a circuit diagram of a battery charging unit, in accordance with the invention.

The power pack unit of which the circuit is illustrated in Figure 1 comprises a battery 10, for example a 12-volt sealed lead acid battery of appropriate rating for example 6, 10 or 24 amp hours, associated with a device protecting it against overdischarge, in the form of a battery voltage monitoring circuit. The battery and associated circuitry is conveniently housed in a strong casing fitted with output and input sockets and an indicator for indicating when the unit is being charged. The power pack unit may be portable and a handle is then advantageously fitted to the top of the casing.

The battery 10 is charged preferably by the charging unit of Figure 2 or alternatively by some other suitable supply source, for example, a 12-volt alternator-based vehicle charging system which is connected to the terminals 11,12 of the input socket.

Across these terminals, a Zener diode 14 and a light emitting diode (LED) 15 serving as the charging indicator are connected in series, so that the LED is energised when the battery is receiving a charge, which is delivered to it through a diode 16.

When the battery is to supply an output from terminals 21,22 of the output socket, a switch 24 is manually closed. Connection through to the terminals 21 is however conditional upon the closure of contacts 25 of a relay 26 included in the protection or monitoring device. This device provides that the battery voltage is applied to one input of a comparator 27 by way of a potential divider comprising resistors 29 and 30 and a variable resistor 31. A reference or trip voltage obtained by way of Zener diodes 32 and 34 and resistors 35 and 36, is applied to the other input of the comparator. The comparator 27 is arranged to provide an output when the battery voltage exceeds the reference voltage, and this turns on transistor 37 thereby energising the relay 26 to close the contacts 25 to complete the line through the switch 24 to the output terminal 21.

As discharge of the battery 10 continues, the battery voltage will drop. When it reaches the preset trip voltage, the output of the comparator 27 drops also, so the transistor 37 switches off. The relay 26 consequently ceases to be energised and the battery 10 is disconnected from the output terminal. The need for recharging is thus of course indicated.

Recharging is preferably carried out by means of the charging unit of which the circuit is shown in Figure 2, by connection of its output terminals 41,42 to the input terminals 11,12 of the power pack unit.

The charging unit may be provided with a casing similar to that provided for the power pack unit. It takes its power from the ac mains supply, which is stepped down, say, to 15 volts, by a transformer 44, the transformer output being rectified by a bridge rectifier 45 and smoothed by a capacitor 46. Regulation of this output is effected conventionally by circuitry comprising resistors 50 and 51, a voltage divider 52, and other components 54-57.

Resistors 60 and 61 extend in series across the stabilized voltage output, upstream of the resistor 50, and a reference or trip voltage, is taken from between them and applied to one input terminal of a comparator 62. The other comparator input terminal receives the output of an adjustable voltage divider 64 in series between resistors 65 and 66 across the output terminals 41 and 42, and thus downstream of the resistor 50.

As long as the battery or power pack unit to which the charging unit is connected draws current above a predetermined level corresponding to normal charging, which may be 240 ma for a 12 volt 24 amp hour battery, the output of comparator 62 is low, but it turns high when the current drops below the predetermined level.

The output of the comparator 62 is applied to the base of a first transistor 70, which is consequently turned off during charging, and to a green indicator LED 71 which consequently does not then emit light.

The transistor 70 is in series across the output terminals 41,42 with a resistor 72 and the volt between them is applied to a second, red, indicator LED 74 and to the base of a second transistor 75. During charging, with the first transistor 70 turned off, this voltage is sufficient to illuminate the red LED 74 and the second transistor 75 is held in the on condition.

The transistor 75 is in series with a variable resistor 76 across the resistor 51, which is in series with the resistors 52 and 57 across the output terminals 41 and 42. The effect of the resistor network comprising the resistors 51,52,57 and 76 is to set the output of the charging unit at the charging or "boost" level, for example, 14.7 volts.

As the battery charges, the current demand will decline, and the current flowing through the resistor 50 falls correspondingly, below a level at which the output of the comparator 62 goes high, sufficient to cause the green LED 71 to emit light and to turn on the first transistor 70. The turning on of this transistor provides a low resistance path in place of that through the red LED 74 which consequently ceases to be illuminated. Also, the voltage applied to the base of the second transistor 75 falls away, so this transistor is turned off. The effect of the variable resistor 76 on the resistor network is consequently now removed with the result that the output voltage of the charging unit falls to a maintenance or "float" voltage, for example, 13.8 volts, as required by a 12 volt sealed lead acid battery.

A resistor -77 is connected across the comparator 62, from the terminal receiving the variable input, to provide hysteresis in the switching action, so that the comparator 62 switches cleanly at the trip point.

Thus, the charging unit will be seen to adjust automatically to battery charging requirements and to clearly indicate its condition by means of the LEDs 71 and 74.

The charging unit is set up by adjustment of the voltage divider 64, so that the comparator output is high and the green LED 71 is illuminated. The voltage divider 52 is then set to give the required 13.8 volts or other "float" voltage at the output terminals 41,42.

The voltage divider 64 is then again adjusted to cause the red LED 74 to be illuminated and the green LED 71 to be extinguished. Next, the variable resistor 76 is adjusted to give an output voltage of 14.7 volts or other "boost" voltage. A load is then connected to the charging unit output terminals 41,42 and is set to draw the required trip current. The voltage divider 64 is then adjusted so that the green LED 71 just lights at this current.

It will be evident that the invention can be embodied in ways other than those specifically described with reference to the accompanying drawings.

Claims

1. A battery device comprising a rechargeable battery and control means responsive to battery condition to control at least one of charging and discharge of the battery.

2. A device as claimed in claim 1 wherein the control means is responsive to the current drawn by the battery during charging to adjust the charging voltage supplied to the battery.

3. A device as claimed in claim 2 wherein the control means is arranged to reduce the charging voltage from a first level appropriate to charging to a second lower level appropriate to maintenance of the charge, in response to a predetermined decrease in charging current demand.

4. A device as claimed in claim 2 or 3 wherein the control means is responsive to a control signal obtained by comparison of a voltage dependent on charging current demand with a reference voltage.

5. A device as claimed in claim 4 having a comparator comparing the voltage dependent on the drawn current with a reference voltage, the comparator output controlling the condition of a transistor in a resistance path across the terminals.

6. A device as claimed in claim 5 wherein the control means operates by reducing the effective resistance across terminals at which the charging voltage is supplied when the voltage dependent on demand falls to a predetermined level relative to the reference voltage.

7. A device as claimed in clam 6 wherein the control means operates by opening a low resistance path and modifying a higher resistance path to remove therefrom a variable resistor adjustable to set the charging voltage level.

8. A device as claimed in any preceding claim having means affording a visual indication of the level of the charging voltage.

9. A device as claimed in claim 6 wherein the control means operates by opening a low resistance path and modifying a higher resistance path to remove therefrom a variable resistor adjustable to set the charging voltage level.

10. A device as claimed in any one of claims 5-9 having means for rectifying and regula ti' ng an 8.c.

mains input to supply the charging and reference voltages.

11. A device as claimed in any preceding claim wherein the control means operates to limit discharge of the battery by disconnecting the battery from an output terminal.

12. A device as claimed in claim 11 wherein the control means is operated by a control signal from a comparator comparing battery voltage with a reference voltage derived from the battery voltage.

13. A device for protecting a battery against discharge beyond a predetermined extent, the device comprising comparator for comparing the battery voltage with a reference voltage and for providing an output for a display and/or control function when the battery voltage falls to a predetermined minimum.

14. A device as claimed in claim 13 wherein the comparator output interrupts the battery output when the battery voltage falls to the predetermined minimum.

15. A device as claimed in claim 12, 13 or 14 wherein the comparator output controls the condition of a transistor connected in circuit with a relay of which the contacts are located between the battery and the output terminal.

16. A device as claimed in claim 12, 13, 14 or 15 wherein the reference voltage is derived from the battery voltage.

17. A device as claimed in claim 16 wherein the reference voltage is obtained from circuitry including a zener diode.

18. A device as claimed in any one of claims 12-17 wherein the battery voltage is represented by a voltage derived from voltage divider circuitry connected across the battery.

19. A device as claimed in claim 18 wherein the voltage divider circuitry includes a selectively variable resistor.

20. A battery control device substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.