Battery analyzer

Claim 1

A battery analyzer for analyzing a wet cell battery that is connected to a vehicle engine, including voltmeter means for measuring the voltage from said battery within a narrow range over which the unloaded battery output will vary as a function of specific gravity of the electrolyte of said battery, said voltmeter means comprising; a resistor voltage divider; a circuit for providing an input reference voltage across said divider; a plurality of voltage comparators each receiving as a first input a respective reference voltage obtained from a tap on said divider, said respective reference voltages being of incrementally greater value with respect to each other; input network means for applying to the other input of each voltage comparator a voltage derived from the output of the battery under test; a like plurality of indicator lamps; an output latch connected between the outputs of said comparators and said lamps, said latch, when enabled, causing certain of said lamps to light up to indicate those comparators at which the voltage derived from said battery exceeds the respective reference voltage, said lamps thereby indicating the unloaded battery voltage and hence the electrolyte specific of the battery under test; said circuit for providing a reference voltage comprises; an operational amplifier having a fixed reference voltage applied to the non-inverting input, the output of said amplifier being connected across said divider as said input reference voltage; a feedback resistor connected between a tap of said divider and the inverting input of said operational amplifier to provide negative feedback that stabilizes the voltage at said tap; a thermistor, mounted to sense the temperature of the electrolyte of said battery under test, and connected to the inverting input of said operational amplifier to correct said input reference voltage, and hence the voltage mesurement, for changes in electrolyte temperature; a range detect and latch circuit for changing the range of said voltmeter means when the battery voltage drops under load, said range detect and latch circuit comprising; a flip-flop; means for setting said flip-flop to a first state when the voltage of the unloaded battery is measured, and for setting said flip-flop to a second state in response to reduced voltage from said battery when under load; and a range-change resistor and means for connecting said range-change resistor to the inverting input of said operational amplifier when said flip-flop is set to said second state, said range-change resistor thereby reducing the input reference voltage applied across said divider so that a lower voltage range is measured, said lower range corresponding to that range over which said battery will vary, when loaded, depending on the battery operational condition.