GB1396359A - Battery testing method and apparatus - Google Patents

Abstract

1396359 Measuring the state of charge of a battery K S CHAMPLIN 13 Sept 1972 [14 Sept 1971] 42536/72 Heading G1U [Also in Division H2] The state of charge of a battery is determined by measuring a quantity inversely proportional to its open circuit A.C. impedance, this being effected either by making the battery one arm of a bridge and causing a small oscillatory current with zero mean to pass through it, or by applying a known oscillatory voltage across the battery and arranging that the open circuit battery impedance controls the gain of a feedback amplifier, suitable D.C. blocking capacitors being used in both arrangements. In the first arrangement Fig. 5, the battery under test, which is shown in dotted lines as comprising a perfect battery Vo in series with an open circuit A.C. impedance R' s , forms with resistors R 1 , R 2 and R 3 a bridge having an oscillatory supply (about 100 c/s) V 1 across the horizontal diagonal and an error voltage V 2 across the vertical diagonal, this voltage being scaled by resistors R 6 , R 7 to provide an output error voltage V 3 . The scaling resistor R 7 is coupled to the adjustable part R 5 of resistor R 2 in such a way that the sensitivity of the bridge is maintained constant. Capacitors C 1 , C 2 , C 3 as shown block any D.C. In use the bridge is connected to each lug of the battery by a connector Fig. 7, which is arranged to connect two leads 14, 16 independently to the lug, this being effected by insulating a member 62 of the connector by a fibre washer 54, and the resistor T 2 is adjusted to zeroise the error voltage V 3 . Resistor R 2 is then inversely proportional to the value of the open circuit A.C. impedance R' s . In a practical realisation of this arrangement Fig. 8 (not shown), the source of A.C. (80, 82, 88) is powered by the battery under test and an error voltage amplifier (112, 130) is arranged to drive a meter (32) in such a way that full scale deflection corresponds to zero error. In the second arrangement, Fig. 9, the battery under test is connected as shown and a known A.C. voltage V 1 is applied across it. It can then be shown that the output voltage V e , which can be displayed on a suitable meter, is inversely proportional to the open circuit A.C. impedance R' s independently of the open loop gain of the amplifier. A practical implementation of this arrangement Fig. 11 (not shown) is also described.