This Dump Load Controller circuit can be used to feed excess solar power to an auxiliary load such as a heating resistor. It works in conjunction with the SCC3 charge controller circuit. The dump load circuit monitors the voltage on the PV panel. When the PV has charged the battery and the battery reaches the SCC3 float voltage setting, the SCC3 PV charge current switch circuit turns off and the PV voltage rises. The dump load circuit detects this higher PV voltage and connects the dump load to the PV.
For the optimal dump load power transfer, the value of the dump load resistor should be chosen so that it pulls the PV voltage down to the PV panel's rated maximum power point during full sun conditions. For 12V systems, the dump load circuit should be adjusted so that it activates at a PV voltage of around 15V. The dump load resistor should have a power rating that is greater than the PV panel's maximum output wattage rating.
Keep in mind that tapping into the excess solar dump load power is much less important than getting your main solar battery charging system up and running reliably. Dump power is only available after the main battery becomes fully charged. When dump power is available it comes in short pulses, making it unsuitable for running most electronic devices. Dump load power is mainly useful for heating air or warming the battery compartment in cold climates. A battery will be able to store and release more energy if it is kept warm.
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