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PSU/voltage guard for car fridge

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New Member
I would need a circuit that cuts off the power from the car battery when the voltage falls too much down. I have a small fridge in my car and I've already twice forgot to unplug it, with the result that the battery gets too empty for the car to start.

So I would need a circuit which connects between the 12v outlet and the fridge, and disconnects the power when the voltage falls to about 11.7v, and if possible reconnects when the power rises a bit above it. It should take 3-4A.

I've looked at this low voltage disconnect circuit but I would like to make one which would be a little more simple, with less components. Does anyone have any good ideas or example circuits?


Active Member
You might find it better to buy a leisure battery instead, perhaps an 80 amp hour one. Car batteries are not designed for this sort of discharge, they are designed to deliver a lot of power very quickly.


Well-Known Member
Most Helpful Member
Here is something that I built for testing 12V batteries for capacity. It switches off the relay (and the load) when the battery voltage falls below a preset level. You can wire the relay contacts either on the high side or low side of your load. Use a small relay, so that the power required to hold in the coil is small compared to your load.


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