BATTERY-STRING MIDPOINT VOLTAGE MEASUREMENT APPARATUS AND METHOD

A mid-string voltage sensor is disposed in proximity to a storage-battery string and determines an error signal between the expected mid-string voltage and the actual mid-string voltage to aid in detecting faults in one or more of the batteries of the string. Each sensor is connected to or close to the battery string terminals and to a terminal at the midpoint of the group of batteries connected in series. The arrangement suppresses errors due to common-impedance coupling, and the measured voltages are decoupled from the battery system, prior to determining the error. A fractional error voltage is derived using a logarithmic ratio amplifier so that the error signal determination is performed at the sensor, with the resultant error signal suitable for coupling to a battery health monitor.