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This project helps to optimize the 12V lead-acid (SLA) battery life as it prevents the battery from going into deep discharge. It is very important to disconnect the load before the battery enters into deep discharge as this may destroy or damage the battery cells. The circuit shown here turns off the load before the battery enters deep discharge and avoids a further (deep) discharge that can shorten the SLA battery life. Once the battery is recharged or replaced you need to push a reset switch to power ON the load. The predetermined load level is set to 12V, this voltage level is proportional to the battery voltage which is determined by resistor divider R2, and R9. Once the voltage falls below the setpoint (12V) it disconnects the load, the load-battery connection remains open until the system receives a manual reset command using tactile switch SW1.

The circuit drains 5uA + PWR LED D2 5mA, so the circuit can remain in that state for an extended period without causing a deep discharge of the battery. Users may not use LED D2 if not required. The circuit is capable to drive continuous load up to 5A and can provide more power with forced air cool to the MOSFET Q1. Connector CN1 is optional if the user wants to use TO220 MOSFET. The project is ideal for 1Ah to 10Ah 12V lead-acid batteries. Low ohm MOSFET is used to provide continuous maximum current output.”

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