The SPC3 Low Voltage Disconnect (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. This circuit can be used to perform this task.
When the sun is shining on the PV and the battery starts to charge, the PV voltage will be around 0.5V above the battery voltage. When the PV voltage rises above the adjustable setpoint, the op-amp comparator circuit will change states and turn on the 2N3904 transistor. The transistor will ground the SPC3 On switch, causing the SPC3 load control circuit to turn on. The turn-on adjustment should be set to activate the comparator when the battery voltage rises somewhat above the SPC3 LVD setpoint, this will prevent oscillation. The load turn-on circuit is isolated from the battery via diode SD1 on the SPC3 so it will not draw any any battery current when the LVD has shut down the load.
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