Apparatus for accurately measuring battery voltage

摘要

A circuit for measuring voltage of a battery or group of batteries whose terminals are not directly accessible. The battery or group of batteries can have three leads. First and second leads are connected to the voltage output of the battery and the third lead is connected to the return of the battery. The three leads may terminate in a three prong plug which may plug into a printed circuit board to form a module. The module can be connected into a rack via an edge connector. A battery voltage measurement circuit can be located on another printed circuit board which is also plugged into the rack. This other printed circuit board may be interconnected to the battery module by wire traces within the rack. Thus, there are one or more first connectors between the first lead of the battery or group of batteries and the charger. There are one or more second connectors between the second lead of the battery or group of batteries and an input of the voltage measurement circuit. There are also one or more third connectors between the third lead of the battery or group of batteries and ground. A first portion of the voltage measurement circuit measures a voltage across the one or more first connectors and the one or more second connectors. A second portion of the voltage measurement circuit determines a difference between the voltage across the one or more first connectors and the one or more second connectors and a voltage measured across the one or more second connectors, the battery and the one or more third connectors to indicate an approximate voltage of the battery or group of batteries. There is negligible voltage drop across the one or more second connectors. Thus, the circuit accurately measures the battery voltage during charging, because it cancels significant voltage drops across the intervening connectors.