GB2147109A - Battery charge monitor - Google Patents

Abstract

A battery charge monitor comprises a shunt 4, adapted to be inserted between the battery 2 and load to sense the flow and direction of current through the shunt, the output of the shunt having the same polarity as that of the current sensed; a voltage to current amplifier 5 connected to the output of the shunt; and two current to pulse generators 6, 7, which produce pulse frequencies proportional to the input current, connected to the output of the voltage to current amplifier. One current to pulse generator produces its signal when its input is in a positive going sense, while the other produces its signal when its output is in a negative going sense. The output signals from the two current to pulse generators are fed through a frequency divider circuit 8 before being fed to a counter 9 to indicate 10 the percentage charge of the battery. <IMAGE>

Description

SPECIFICATION Baccam unit The present invention relates to a battery charge monitor which we shall call a Battery Ampere-hour Charge Control Automatic Monitor or Baccam Unit which is a device which continuously monitors the state of capacity of a storage battery and provides control interface with the regulated rectifier (charger) in order to maintain the state of charge of the battery in a 100% condition.

In telephone exchanges, electricity generating stations and computer installations, to name a few, lead acid and/or nickel cadmium storage batteries are used to provide a continuity of supply to the load for a limited period when the normal A.C. supply fails. Such loads are termed "essential loads" and, as their name implies have to be maintained in operation irrespective of the normal A.C. supply condition until such time that they can be closed down in a orderly manner. The ampere-hour capacity of the storage battery is selected to provide the load power requirements for the time duration required after A.C. supply failure. Depending on the nature of the load, this may be for a few minutes or may extend upto a period of 24 hours or more as is the case with remote unattended radio-repeater stations.

The storage battery consists of a number of individual cells usually connected in series and sometimes in a series/parallel configuration, the number of cells so connected determines the voltage of the supply system and these are usually arranged for nominal 24, 48, 11 10 and 220 volt systems. The capacity of the storage battery (and cell) is expressed in 'ampere-hours' at standard time rates and indicates the amount of electrical energy which can be discharged from the battery for a given time period without the terminal voltage of the storage battery (and cell) falling below a specified voltage level.

Prior art devices are known which use a reversing D.C. kilowatt hour meter which measured and indicated the electrical energy delivered to and removed from the storage battery.

Such meters are similar in many respects to the conventional A.C. kilowatt hour meters installed at the supply input point on all premises using electrical energy. However they differ as follows:- 1. They can only be used on a direct current (D.C.) supply system.

2. The meters are of a reversing type ie, movement of electrical energy in one direction causes the meter count to increase and movement in the opposite direction causes the count to decrease.

The Baccam unit has been designed to provide a replacement for these earlier reversing D.C. kilowatt hour meters. The Baccam unit is a static unit employing current microelectronic technology and as such offers many advantages that were not possible in the electro-magnetic type of kilowatt hour measurement.

In one broad form the invention comprises a battery charge monitor comprising: a shunt, adapted to be inserted between the battery and load to sense the flow and direction of current through the shunt, the output of the shunt having the same polarity as that of the current sensed; a voltage to current amplifier connected to the output of the shunt; and two current to pulse generators, which produce pulse frequencies proportional to the input current, connected to the output of the voltage to current amplifier; one current to pulse generator produces its signal when its input is in a positive going sense, while the other produces its signal when its input signal is in a negative going sense;; the output signals from the two current to pulse generators being fed through a frequency divider circuit before being fed to a counter to indicate the percentage charge of the battery.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a float charged D.C. supply system utilising an embodiment of the present unit; and Figure 2 is a schematic diagram of an embodiment of the present invention.

As shown in Fig. 1 the regulated rectifier (charger) 1 accepts the standard alternating current supply and converts this into a direct current having a very stable voltage. The direct current output voltage is maintained within close limits for wide voltage variation in incoming A.C. supply voltage and for wide variations in the load demand. The output voltage of the regulated rectifier 1 is controlled at two or more voltage levels, one designated 'float voltage' which is the normal operating condition and the other "boost voltage' which is some 15-18% higher than the float voltage and is used for returning the final charging current to the battery 2 during charging conditions. As a minimum the regulated rectifier 1 should be equipped with low/high output voltage alarms and a means of automatically limiting the output current under faulty conditions.

In normal operation the regulated rectifier 1 supplies the load demand and little or no energy flows into the fully charged battery.

This is termed 'float charged'. However, in the event of the normal A.C. supply being interrupted and the regulated rectifier 1 ceasing to operate, the load 3 is then supplied directly from the storage battery 2 and no loss of supply to the load 3 occurs. Electrical current from the storage battery 2 is prevented from feeding back into the regulated rectifier by the nature of its design and the solid state components used.

The storage battery continues to supply the load until: (a) it reaches a fully discharged condition, at which time the battery voltage has fallen to a predetermined level beyond which the load cannot tolerate, or (b) the A.C. supply is restored.

In the case of the former condition and depending on the nature of the load, a diesel alternator set can be brought into operation to provide a standby supply until the normal A.C. supply is restored. With such an arrangement the output of the alternator is connected to the input of the regulated rectifier and the load continues to receive its supply in the normal manner.

When the A.C. supply is restored, the energy removed from the storage battery has to be replaced, usually in as short a time as possible.

The Baccam unit continuously displays the percentage capacity remaining in the storage battery and initiates corrective action when this is less than 100% capacity.

The electrical shunt 4 shown connected in the common line to the storage battery 2 generates a millivolt signal across its terminals. The amplitude of which is proportional to the current flowing through the shunt 4 and a polarity which is dependent on the direction of flow of current through the shunt.

Hence the shunt provides a convenient means of measuring and indicating whether energy is being drawn from or returned to the storage battery.

Reference is made to Fig. 2 which shows the basic diagram of the Baccam unit.

A voltage to current amplifier 5 receives at its input the millivolt signal developed across the terminals of the shunt 4 and produces at its output a current which is proportional to the millivolt signal and having the same polarity as the input signal. The output of the voltage to current amplifier 5 is connected to the input of two current to pulse generators 6, 7 which produce at their outputs a pulse frequency proportionate to the input current.

One current to pulse generator 6 conducts while its input current is in a positive going sense, and the other 7 while its input current is in a negative going sense. Frequency divider circuits 8 divide both the current to pulse generator frequencies by 1 63840 and the final output count is applied to the counter circuits 9. A polarity signal 14 derived from the internal shunt 4 is also applied to the counter circuits 9, this causes the output count to be incremented during charge conditions and decremented during discharge conditions. The output from the counter circuits is arranged to drive a three digit LED (light emitting diode) display 10 to indicate state of charge of the storage battery.

Three minature relays fitted within the unit are actuated for the following conditions: 1) High Level Relay 13 Energised when the count equals 100 (1 00%).

de-energised when the count equals 99.

2) Low Level Relay 11.

Preselectable in increments of 10 counts through the range of 10 to 90 counts. The relay is energised when the count is one less than the preselected count (49 for a preselection of 50) and is released when the count equals the preselected count.

3) Boost Relay 1 2 Energised when the Low Level Relay is energised, released when the High Level Relay is energised.

Contacts on these relays are used to interface with the charger control circuits to provide automatic recharging of the battery and to provide remote indication of the battery status.

Five LED indicators fitted to the front panel of the unit provide indication for:- 'Charging' 'Discharging' 'Low Level Alarm' 'Boost On' '100% Capacity' Two pushbuttons fitted on the front panel provide rapid manual count up of the display to assist with initial calibration and testing of the unit.

The unit is designed to operate from nominal 24 and 48 volt D.C. battery supplies and imposes a load of 4.8 watts at 24 volts. It can be arranged to operate from higher voltages.

As previously stated the storage battery capacity 'C' is expressed in ampere hours ie.

the number of amperes the battery will delivery for a given time period. With the Baccam unit 'C' represents a total count of 1 6.384 x 106 before count division occurs, therefore it follows that if the battery supply is required for 5 hours (C/5) some 3.2768 X 106 counts per hour or 91().22Hz are required if the battery is delivering full load current.

Calibration of the Baccam unit for any given D.C. supply system is carried out as fol vows: 1. Calculate the full load discharge current C I = where T C = Battery capacity ampere hours.

T= Discharge time in hours.

2. Calculate the actual millivolt signal from the selected shunt using the full load discharge current calculated in 1.

3. Calculate the count frequency in seconds from 16.384X 106 = Hz TX 60 x 60 where T = Discharge time in hours.

Hz = Frequency in seconds.

4. Feed the millivolt signal calculated in 2 into the Baccam in the "discharge" direction.

Adjust the gain potentiometer (refer Fig. 2) on the voltage/current amplifier until the count frequency calculated in 3 is generated at the test point provided. This corresponds to a 1000 Hz millisecond time interval between count pulses.

5. Feed the millivolt signal calculated in 2 times the battery efficiency (mV X efficiency) into the Baccam unit in the "charge" direction.

6. Adjust the gain potentiometer on the "charge" current/pulse generator until the count frequency calculated in 3 is generated at the test point provided.

The Baccam unit will then indicate 100% charge when the discharge energy plus losses due to battery efficiency has been returned to the battery.

With a fully charged battery connected to the supply system, the three digit LED display is set to read 100%. The Baccam unit will now continuously indicate the state of charge of the battery to an accuracy of 1%.

Claims (6)

1. A battery charge monitor comprising: a shunt, adapted to be inserted between the battery and load to sense the flow and direction of current through the shunt, the output of the shunt having the same polarity as that of the current sensed; a voltage to current amplifier connected to the output of the shunt; and two current to pulse generators, which produce pulse frequencies proportional to the input current, connected to the output of the voltage to current amplifier; one current to pulse generator produces its signal when its input is in a positive going sense, while the other produces its signal when its input signal is in a negative going sense; the output signals from the two current to pulse generators being fed through a frequency divider circuit before being fed to a counter to indicate the percentage charge of the battery.

2. A battery charge monitor according to claim 1 further comprising charger control circuit to provide automatic recharging of the battery.

3. A battery charge monitor according to claim 2 comprising a high level control relay which is energised when the counter indicates 100% charge of the battery and is de-energised when the counter indicates 99% charge of the battery.

4. A battery according to claim 2 or 3 comprising a low level relay which is preselectable in increments of 10% of the battery charge through the range of 10 to 90% of the battery charge and is energised when the counter indicates 1 less than the preselected percentage reading and is released when the counter indicates the preselected percentage reading.

5. A battery according to claim 4 comprising a boost relay which is energised when the low level relay is energised and is released when the high level relay is energised.

6. A battery charge monitor substantially hereinbefore described with reference to the accompanying drawings.