Battery-string midpoint voltage measurement apparatus and method

A midpoint voltage sensor comprising:

• a first input terminal configured to be attachable to a battery terminal of a first end of a storage-battery string;
• a second input terminal configured to be attachable to a battery terminal of a second end of the storage battery string;
• a third input terminal configured to be attachable to a battery terminal located at a midpoint of the storage battery string;
• a first output terminal configured to be connectable to an input of a health monitoring system,
• a first electronic circuit configured to produce a voltage reference signal proportional to half of a voltage between the first input terminal and the second input terminal;
• a second electronic circuit configured to produce a voltage proportional to the voltage between the second input terminal and the third input terminal;
• and,
• an analog logarithmic ratio circuit having an output of the first electronic circuit as a first input voltage and an output of the second electronic circuit as a second input voltage, and a voltage at an output terminal equal to a difference between a logarithm of the first input voltage and a logarithm of the second input voltage, the output communicating with the output terminal of the midpoint voltage sensor.

A method of monitoring a midpoint voltage of a storage-battery string of a plurality of storage-battery strings, the method comprising:

• providing a midpoint voltage sensor for each monitored storage-battery string, the midpoint voltage sensor comprising:
• a first input terminal configured to be attachable to a battery terminal at a first end of the storage-battery string;
• a second input terminal configured to be attachable to a battery terminal at a second end of the storage-battery string;
• a third input terminal configured to be attachable to a battery terminal located at a midpoint of the storage-battery string;
• a first output terminal configured to be connectable to an input of a health monitoring system,
• a first electronic circuit having an input circuit configured to produce a voltage reference signal proportional to half of a voltage between the first input terminal and the second input terminal;
• a second electronic circuit having an input circuit configured to produce a voltage proportional to the voltage between the second input terminal and the third input terminal;
• an analog logarithmic-ratio circuit having an output of the first electronic circuit as a first input voltage and an output of the second electronic circuit as a second input voltage, and a voltage at an output terminal equal to a difference between a logarithm of the first input voltage and a logarithm of the second input voltage, the output terminal communicating with a first output terminal of the midpoint voltage sensor;
• attaching the first input terminal to the first end of the storage-battery string, the second input terminal to the second end of the storage battery string and the third input terminal to the midpoint of the storage-battery string;
• and,
• acquiring and analyzing an error signal at the first output terminal.

A midpoint voltage sensor, comprising:

• a first input terminal, connectable to a first end of a string of two or more batteries;
• a second input terminal. connectable to a second end of the string of two or more batteries;
• a third input terminal, connectable to a midpoint of the string of two or more batteries;
• an output terminal;
• a reference voltage circuit;
• a first differential amplifier;
• a second differential amplifier;
• and,
• a logarithmic ratio circuit,
• wherein the reference voltage circuit outputs a reference voltage derived from a difference between a voltage at the first input terminal and a voltage at the second input terminal;
• wherein the reference voltage and the voltage between the third input terminal and either the first input terminal or the second input terminal are input to the logarithmic ratio circuit, and an output of the logarithmic ratio circuit is connected to the output terminal.