Fridge Defrost Timer with Solar Trigger Option

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This fridge defrost timer is triggered from my solar panel system so the fridge defrost cycle will run only when I have excess power.

It can be triggered from any 7 to 25vdc signal. I used the battery vent fan signal from my Outback Battery charger.

It powers itself from the signal or from a micro-amp parasitic source. I did not want to use a power adapter which wastes power all day and is too big for the container. had a key part: cpc1030N, which is a surface mount Clare opto-isolated relay 0.85mA 1.4 input, controlling 120vac 120mA . and the prototyping board.

The two 10 farad super capacitors are $4 each at part #589-1002-ND. Project box: #SR123-IA-ND. Don't use Nichicon. They lose charge too quickly. The relay is: JQX-13F (be sure to select the 120vac coil JQX-13F A110-2Z1) $7.

circuit: board etch pattern:

Later I discovered my mechanical timer only ran when the compressor was on. Plus, I added capacitors on the chip reset pins to stop electrical interference triggering false resets. So here is a revised schematic for that kind of defrost:


FridgeTimer board layout.png