Building a fridge0 involves switching AC power with a relay under computer control. High voltage needs a suitable enclosure for safety. Other things you may want to put in the enclosure include:

  • AC power outlet(s)
  • Connections for temperature sensors
  • The embedded computer itself
  • And any other small hardware that needs to be close to the fridge

You may want to locate your fridge0 on a porch or other location outside to avoid it needing to run as much in the winter. So it's a good idea to plan for a water resistent enclosure.

A NEMA compliant, waterproof, locking enclosure is easy and inexpensive to find in a variety of shapes and sizes. Recommended.

Joey Hess's fridge0

I used a fairly large enclosure, and wish it had been even larger. I also wish it had more places for screws.

It has two relays each powering their own AC outlet; I use the second one as a spare, or perhaps for a freezer or AC powered dump load.

Notice that the black AC wire is connected to the relay. That is the hot wire. You want to interrupt the hot wire, not the neutral wire. Consult your local code when dealing with AC wiring.

Since this is outdoors, it needs to be GFCI protected; it plugs into the outdoor AC outlet next to it, which contains a GFCI. It would actually be more efficient to have put the GFCI outlet after the relay, because a GFCI outlet has some phantom load to run the protection circuit, perhaps as much as 3-5 watts. (But I don't know if that would be a good idea as far as the ground fault protection goes.) As it is, that GFCI outlet is powered whenever the inverter is turned on, even when fridge0 is not running.

The computer is not located in the enclosure, it's in the house about 40 feet away, since it needed to be close to the charge controller and inverter.

The custom circuit board simply connects up the relays' control lines, and splits an incoming onewire bus out to 3 temperature probes. I wish it fit more. Note the added resistors on the onewire signal pins, which are to try to dampen echos and avoid some sensor read errors.

I also had to adjust the resistor size on the relay boards to make the relays work reliably at this distance from the computer. Before fixing that, the relays would sometimes chatter or not turn on all the way. At one point I measured AC voltage split 50-50 between the NO and NC pins of the relay that was on half way, which seemed like it could lead to ugly failure modes. So make sure the relay turns on crisply and fully before plugging anything into it.


Please add your hardware enclosure information here if you do a fridge0 build.