Battery Charger Control Circuit

Battery charger control circuit is very useful now-a-days. You need not follow on battery charging or disconnect from ac power for avoiding over charge. This circuit is used to charge battery when the battery voltage drops
below the minimum voltage that you want to connect it to a charger.
When the battery voltage reaches the maximum voltage you want the
charger to be connected.

This
circuit is shown in figure. Let your battery voltage is 15 volt. When
Ei drops below 10.5 V, V0 goes negative, releasing the relay to its
normally closed position. The relay’s normally closed (NC) contacts connect the charger to battery Ei. Diode D1 protects the transistor against excessive reverse bias
when V0 = -Vsat. When the battery charges to 13.5 V, V0 switches to
disconnect the charger. Diode D2 protects both op-amp and resistor
against transients developed by the relay’s collapsing magnetic field.

Suppose that the application requires an inverting voltage level detector with hysteresis.
That is V0 must go low when Ei goes above Vut and V0 must go high when
Ei drops below Vlt. For this application, do not change the circuit or
design procedure for the non-inverting voltage level detectors, simply
add an inverting amplifier, or inverting comparator, to the output Vo.