Method and apparatus for determining to which battery cell in a string of battery cells a test instrument is connected

1. In a system having a plurality of substantially identical rechargeable battery cells arranged in at least one string between a pair of busses, said at least one string having a plurality of serially connected battery cells to form a battery system, a method for determining across which battery cell in one of said at least one string a test instrument is connected, the method comprising the steps of:

a) determining the average voltage of a battery cell in said one of said at least one string;

b) measuring the voltage from one of said pair of busses to the side of said test instrument closest to the other of said pair of busses;

c) setting n=1;

d) multiplying the average voltage by (n+0.5) to obtain V HI ;

e) multiplying the average voltage by (n−0.5) to obtain V LO ;

f) determining whether the measured voltage is between V HI and V LO ; and

g) if the measured voltage is not between V HI and V LO ,

setting n=n+1 and repeating steps d)-f) until it is determined that the measured voltage is between V HI and V LO ;

wherein n is an integer, V HI is a calculated variable representing the high end of a voltage range, and V LO is a calculated variable representing the low end of a voltage range;

whereby when it is determined that the measured voltage is between V HI and V LO , this indicates that the test instrument is connected across the n th battery cell counting from said one of said pair of busses.

2. A test instrument for taking a measurement across a selected battery cell in a string of battery cells between a pair of busses and determining to which battery cell in said string the test instrument is connected, wherein the test instrument is provided with the average voltage of a battery cell in said string, the test instrument comprising:

first and second measurement leads adapted for connection across said selected battery cell;

a third lead adapted for connection to one of said pair of busses;

a voltmeter connected between said third lead and that one of said first and second measurement leads which is adapted to be connected furthest from said one of said pair of busses; and

means for determining what integral multiple of said average voltage is closest to the voltage measured by said voltmeter.

3. A test instrument for taking a measurement across a selected battery cell in a string of battery cells between a pair of busses and determining to which battery cell in said string the test instrument is connected, wherein the test instrument is provided with the average voltage of a battery cell in said string, the test instrument comprising:

a first lead adapted for connection to one of said pair of busses;

a second lead adapted for connection to that terminal of said selected battery cell which is closest to said one of said pair of busses;

a third lead adapted for connection to the other terminal of said selected battery cell;

a first high impedance network connected between said first and third leads;

a second high impedance network connected between said second and third leads;

an analog to digital converter having first and second inputs;

a first amplifier stage having its input connected to said first lead and its output connected to said first input of said analog to digital converter;

a second amplifier stage having its input connected to said second lead and its output connected to said second input of said analog to digital converter; and

a microprocessor connected to an output of said analog to digital converter and operative to determine to which battery cell in said string the test instrument is connected by performing the steps of:

a) determining the voltage between said first and third leads;

b) setting n=1;

c) multiplying the average voltage by (n+0.5) to obtain V HI ;

d) multiplying the average voltage by (n−0.5) to obtain V LO ;

e) determining whether the determined voltage is between V HI and V LO ; and

f) if the determined voltage is not between V HI and V LO , setting n=n+1 and repeating steps c)-e) until it is determined that the determined voltage is between V HI and V LO ;

wherein n is an integer, V HI is a calculated variable representing the high end of a voltage range, and V LO is a calculated variable representing the low end of a voltage range;

whereby when it is determined that the determined voltage is between V HI and V LO , this indicates that the test instrument is connected across the n th battery cell counting from said one of said pair of busses.