GB2109182A - Monitoring battery charging - Google Patents

Abstract

A circuit for monitoring the charging of a bank B1, B2 of battery cells having a centre tap X includes two potential dividers VR1, VR2 connectible across the bank and two differential amplifiers A, B each having one input 2, 4 connected to the centre tap X and the other input 1, 3 connected to the slider of a respective one of the potential dividers VR1, VR2 the outputs of the amplifiers A, B being connected in parallel to supply current to a fault indicating circuit LED1, LED2, TR1, the arrangement being such that when the sliders of the two potential dividers VR1, VR2 have been adjusted to supply sufficient current to the indicating circuit any variation of the potential of the centre tap in either direction relative to the ends of the bank, eg. due to a cell going abnormally high or low in resistance, will cause the current through the indicating circuit to fall thus indicating the fault. In the event of a fault, transistor TR1 turns off and relay RL1 drops out to signal the fault and/or cause charging to be stopped. <IMAGE>

Description

SPECIFICATION Electrical monitoring circuit This invention relates to a circuit for monitoring the charging of a bank of battery cells in order to detect the failure of any cell.

The present invention consists in a circuit for monitoring the charging of a bank of battery cells having a centre tap, wherein the monitoring circuit includes two potential dividers connectible across the bank and two differential amplifiers each having one input connected to the centre tap and the other input connected to the slider of a respective one of the potential dividers, the outputs of the amplifiers being connected in parallel to supply current to a fault indicating circuit, the arrangement being such that when the sliders of the two potential dividers have been adjusted to supply sufficient current to the indicating circuit any variation of the potential of the centre tap in either direction relative to the ends of the bank will cause the current through the indicating circuit to fall and the fault indicated.

In carrying the invention into effect according to one convenient mode by way of example, the accompanying shows diagrammatically a monitoring circuit connected to a bank of battery cells being charged by a charging current (not shown), the bank having a centre tap at X dividing the bank into two halves B1 and B2.

Resistors R1 and R2 and zener diodes ZD1 and ZD2 are connected so as to devise t 5.6V supplies for differential amplifiers A and B. Potentiometers VR1 and VR2 are connected in parallel and in series with zener diodes ZD3 and ZD4 across the bank B1, B2.

The system is set up initially by adjusting VR1 to a point where the potential on input 1 is more negative than that on input 2 by a few millivolts so that the output of amplifier A goes positive in relation to the centre tap line and current flows through R4 and R11 illuminating LED1. The voltage drop across R11 will be about 0.7V but will not be sufficient to operate TR1 due to the voltage drop across D1.

VR2 is then adjusted in similar manner so that the voltage on input 3 is made positive than that on input 4 to give a positive output on amplifier B and current will flow through LED2, R9 and R1 1. When the outputs of both amplifiers A and B are positive, the voltage drop across R11 will be doubled to about 1 .4V and will be sufficient to operate transistors TR1 which will operate relay RL1 via diode D2. The contacts of RL1 are arranged to control the main charging circuit so that charging can take place.

If any cell in the half B1 of the bank is faulty and goes abnormally high resistance, or any cell in half B2 goes abnormally low resistance, or there is any other change in resistance, for example due to a battery link fault, then the centre tap will go in a negative direction with respect to the slider of VR1 so that effective negative input on input 1 of amplifier A will be lost, and the removal of the positive output of amplifier A will cause the voltage across R11 to fall with the consequent switching off of transistor TR1 and release of relay RL1 which can be used to signal the fault and/or cause charging to be stopped. Conversely, low resistance of a cell in half B1 or high resistance in half B2 will cause the positive output of amplifier B to be normal with consequent release of relay RL2.An out of balance condition in either direction will thus be detected and indicated by release of relay RL2.

In cases where the voltage across the battery bank B1 ,B2 is not appropriate to provide the f 5.6V supply and the supply to relay RL1 then separate external power supplies may be provided.

CLAIMS (Filed on 4. 10. 82) 1. A circuit for monitoring the charging of a bank of battery cells having a centre tap, wherein the monitoring circuit includes two potential dividers connectible across the bank and two differential amplifiers each having one input connected to the centre tap and the other input connected to the slider of a respective one of the potential dividers, the outputs of the amplifiers being connected in parallel to supply current to a fault indicating circuit, the arrangement being such that when the siiders of the two potential dividers have been adjusted to supply sufficient current to the indicating circuit any variation of the potential of the centre tap in either direction relative to the ends of the bank will cause the current through the indicating circuit to fall and the fault indicated.

2. A circuit for monitoring the charging of a bank of battery cells, substantially as described with reference to the accompanying drawing.

New claims or amendments to claims filed on 16.2.83.

Superseded claims New or amended claims: 2. A circuit as claimed in claim 1, wherein the indicating circuit includes a resistor through which can flow the current from the outputs of both amplifiers, the arrangement being such that the voltage produced across the resistor is sufficient to maintain a relay operated so that charging can take place only when current flows from both amplifiers through the resistor.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrical monitoring circuit This invention relates to a circuit for monitoring the charging of a bank of battery cells in order to detect the failure of any cell. The present invention consists in a circuit for monitoring the charging of a bank of battery cells having a centre tap, wherein the monitoring circuit includes two potential dividers connectible across the bank and two differential amplifiers each having one input connected to the centre tap and the other input connected to the slider of a respective one of the potential dividers, the outputs of the amplifiers being connected in parallel to supply current to a fault indicating circuit, the arrangement being such that when the sliders of the two potential dividers have been adjusted to supply sufficient current to the indicating circuit any variation of the potential of the centre tap in either direction relative to the ends of the bank will cause the current through the indicating circuit to fall and the fault indicated. In carrying the invention into effect according to one convenient mode by way of example, the accompanying shows diagrammatically a monitoring circuit connected to a bank of battery cells being charged by a charging current (not shown), the bank having a centre tap at X dividing the bank into two halves B1 and B2. Resistors R1 and R2 and zener diodes ZD1 and ZD2 are connected so as to devise t 5.6V supplies for differential amplifiers A and B. Potentiometers VR1 and VR2 are connected in parallel and in series with zener diodes ZD3 and ZD4 across the bank B1, B2. The system is set up initially by adjusting VR1 to a point where the potential on input 1 is more negative than that on input 2 by a few millivolts so that the output of amplifier A goes positive in relation to the centre tap line and current flows through R4 and R11 illuminating LED1. The voltage drop across R11 will be about 0.7V but will not be sufficient to operate TR1 due to the voltage drop across D1. VR2 is then adjusted in similar manner so that the voltage on input 3 is made positive than that on input 4 to give a positive output on amplifier B and current will flow through LED2, R9 and R1 1. When the outputs of both amplifiers A and B are positive, the voltage drop across R11 will be doubled to about 1 .4V and will be sufficient to operate transistors TR1 which will operate relay RL1 via diode D2. The contacts of RL1 are arranged to control the main charging circuit so that charging can take place. If any cell in the half B1 of the bank is faulty and goes abnormally high resistance, or any cell in half B2 goes abnormally low resistance, or there is any other change in resistance, for example due to a battery link fault, then the centre tap will go in a negative direction with respect to the slider of VR1 so that effective negative input on input 1 of amplifier A will be lost, and the removal of the positive output of amplifier A will cause the voltage across R11 to fall with the consequent switching off of transistor TR1 and release of relay RL1 which can be used to signal the fault and/or cause charging to be stopped. Conversely, low resistance of a cell in half B1 or high resistance in half B2 will cause the positive output of amplifier B to be normal with consequent release of relay RL2.An out of balance condition in either direction will thus be detected and indicated by release of relay RL2. In cases where the voltage across the battery bank B1 ,B2 is not appropriate to provide the f 5.6V supply and the supply to relay RL1 then separate external power supplies may be provided. CLAIMS (Filed on 4. 10. 82)

1. A circuit for monitoring the charging of a bank of battery cells having a centre tap, wherein the monitoring circuit includes two potential dividers connectible across the bank and two differential amplifiers each having one input connected to the centre tap and the other input connected to the slider of a respective one of the potential dividers, the outputs of the amplifiers being connected in parallel to supply current to a fault indicating circuit, the arrangement being such that when the siiders of the two potential dividers have been adjusted to supply sufficient current to the indicating circuit any variation of the potential of the centre tap in either direction relative to the ends of the bank will cause the current through the indicating circuit to fall and the fault indicated.

2. A circuit as claimed in claim 1, wherein the indicating circuit includes a resistor through which can flow the current from the outputs of both amplifiers, the arrangement being such that the voltage produced across the resistor is sufficient to maintain a relay operated so that charging can take place only when current flows from both amplifiers through the resistor.

2. A circuit for monitoring the charging of a bank of battery cells, substantially as described with reference to the accompanying drawing.

New claims or amendments to claims filed on 16.2.83.

Superseded claims New or amended claims: