SPC3 Turn-on circuit

Automatic SPC3 Load Turn-on

(C) G. Forrest Cook 2015

The SPC3 LVD function is automatic, when the battery voltage drops below the LVD setpoint, the load is turned off. The standard SPC3 circuit requires a manual operation of the switch to turn the load back on after the battery recharges and the voltage rises. For some applications, it may be desirable to have the circuit turn back on automatically. The following circuit can be used to perform this task.

The load turn-on uses a voltage comparator circuit with a transistor switch. When the battery voltage rises above an adjustable setpoint, the op-amp turns on the 2N3904 transistor. The transistor connects the SPC3 On switch to ground, turning on the SPC3 load control circuitry. The turn-on adjustment should be set to activate the circuit when the battery voltage rises somewhat above the SPC3 LVD setpoint to prevent oscillation.

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