Solar electric hot water conversion

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Joined: 05/06/2004
Location: Australia
Posts: 4860
Posted: 12:18am 15 May 2020      

Yeah that's what I thought would be the case. I was surprised at just how hot mine got, and ended up fitting a 12v 100mm PC fan. I watched the heatsink temperature for a few days and it never got over 45c with the fan.

Will check on it in summer, I suspect the heat may be a problem so I'll just need a bigger heat sink. Another option would be a thermal switch on the heat sink to switch off the mosfet, but leave the fan running, if it all gets to hot.

The risk is if the mosfet fails and goes short circuit, the tank will continue to heat up even if the tank thermostat is open. That's bad. Provided the pressure release valve is working OK it should be safe, but things are getting dangerous.

You could add a alarm circuit. If the thermostat is open, but the element is still has power, sound a warning buzzer. Probably not needed, I'll see how it goes through summer.