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LED 12 Volt
Lead Acid Battery Meter
In the
circuit below, a quad voltage comparator (LM339) is used as
a simple
bar graph meter to indicate the charge condition of aа 12
volt, lead
acid battery. A 5 volt reference voltageа
isа connected
to each of
the (+) inputs of theа fourа comparatorsа
andа theа (-)
inputs are
connected to successive points along a voltage divider.
The LEDs
will illuminate when theа voltageа atа
theа negativeа (-)
input
exceeds the reference voltage. Calibration canа
beа doneа by
adjusting
the 2K potentiometer so that allа
fourа LEDsа illuminate
when the
battery voltage is 12.7а volts,а indicatingа
fullа charge
with no
load on the battery. At 11.7 volts, the LEDs should be off
indicating
a dead battery. Each LED represents an approximateа 25%
change in
charge condition orа 300а millivolts,а
soа thatа 3а LEDs
indicate
75%, 2 LEDs indicate 50%, etc. The actualа
voltagesа will
depend on
temperature conditions and battery type, wetа
cell,а gel
cell etc.
Additional information onа batteryа maintenanceа
canа be
found at:
Deep Cycle Battery FAQ
