High sensitivity battery resistance monitor and method therefor

  • US 5,969,625 A
  • Filed: 04/16/1997
  • Issued: 10/19/1999
  • Est. Priority Date: 04/19/1996
  • Status: Expired due to Fees
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First Claim
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1. A method for detecting a deteriorating condition in a plurality of serially connected batteries utilized as a bank of standby batteries coupled in parallel to a battery charger and a DC powered load between a first and a second battery bus comprising the steps of:

  • providing a first audio frequency current transformer for injecting a predetermined signal current and a second audio frequency current transformer for sensing a resultant current signal;

    injecting an audio frequency current as said predetermined signal current via said first audio frequency current transformer into one of said first and second battery busses;

    detecting a current signal at said audio frequency and carried by said one battery bus as said resultant current signal via said second audio frequency current transformer and generating a representative current signal which is related to said injected audio frequency current signal;

    detecting a voltage drop, at said audio frequency, across said first and second battery busses and generating a representative voltage signal which is related to said injected audio frequency current signal;

    when said bank of standby batteries is in a normal, stable operating condition, not when said bank is in a recharging state nor when said bank is supplying DC power to said load in a discharging state, establishing a differential relationship between the representative voltage and the representative current signals; and

    ,determining when said differential relationship exceeds at least one predetermined value and issuing an alarm signal thereat.

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