Description
Source -http://www.bowdenshobbycircuits.info/
In the circuit below, a quad voltage comparator (LM339) is used as a
simple bar graph meter to indicate the charge condition of a 12 volt,
lead acid battery. A 5 volt reference voltage is connected to each of
the (+) inputs of the four comparators and the (-) inputs are connected
to successive points along a voltage divider. The LEDs will illuminate
when the voltage at the negative (-) input exceeds the reference
voltage. Calibration can be done by adjusting the 2K potentiometer so
that all four LEDs illuminate when the battery voltage is 12.7 volts,
indicating full charge with no load on the battery. At 11.7 volts, the
LEDs should be off indicating a dead battery. Each LED represents an
approximate 25% change in charge condition or 300 millivolts, so that 3
LEDs indicate 75%, 2 LEDs indicate 50%, etc. The actual voltages will
depend on temperature conditions and battery type, wet cell, gel cell
etc.
Circuit Diagram
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