Idea for shutting off inverter when fridge is not running.

[Short_Shot]

It's a 12v thermostat, you would have to get clever in order to use that. You might be able to use a 120v relay assuming you can find one that will pass 12v on the switch side. In my search last night most of them have minimum voltages... Honestly I like the simplicity of the design I laid out initially. And as I said, I don't think the fridge could make it all night without passing the max desired temp, so you could just program the temp higher so it stays off longer. I could be wrong though, some refrigerators are pretty well insulated, it might make it...

But... he's using a 12v battery though?

It doesn't matter what is running through the load contacts if the coil and everything else is 12v. Just run it off the battery.

 

[Hedges]

If the fridge and freezer are interconnected as you've stated then you might be good to go for the night. Especially if you can monitor the top and bottom temps, and run that fan you mentioned via 12v power with a custom control setup.

The fans in my freezers are 120VAC, of course.

Top freezer spills air to fridge.
My side-by-side had holes top and bottom. A 1" laptop fan (assuming it survived the environment) could be put over the bottom hole to force circulation whenever fridge rose above target.

Normal operation is refrigerator temperature regulated to setpoint by running compressor to chill freezer section. Baffle controls how much of that spills to fridge. So fridge stays within hysteresis of thermostat and freezer says however much colder.

It's a 12v thermostat, you would have to get clever in order to use that. You might be able to use a 120v relay assuming you can find one that will pass 12v on the switch side. In my search last night most of them have minimum voltages... Honestly I like the simplicity of the design I laid out initially. And as I said, I don't think the fridge could make it all night without passing the max desired temp, so you could just program the temp higher so it stays off longer. I could be wrong though, some refrigerators are pretty well insulated, it might make it...

The HF timer would just turn AC power to the fridge/freezer on or off. For bypass when too warm at night, I would buy a 120VAC mechanical thermostat, uncoil and feed the sensor line into refrigerator (or freezer) compartment, wire its contact to bypass timer.

If it turns out fridge coasts through the night well enough with cold spilled from freezer, I would use this to re-enable compressor if freezer section rose above some target. Because there is no (or not much) phase change, it warms up until something in freezer thaws; temperature rise should pause during that phase change. That's why I'm thinking of brine solution in bottles, tuned to melt colder than target temperature for frozen food but warmer than what temperature the freezer achieves. Freezer temperature is probably a moving target summer vs. winter because thermostat is regulating refrigerator. Baffle set for "colder frozen food" would help achieve frozen brine, but would interfere with spilling cold air to fridge.

 

[Moltensurf]

I was thinking about a way to shut down the inverter when your fridge doesn’t need it and save yourself the sometimes astronomical parasitic loss of the inverter running for no reason. My idea is this:

Use two starter solenoids (like the ones used on old Ford trucks), running parallel between the battery and the inverter. I suppose it could be done on either positive or ground. Then connect a temp sending unit to one of them and connect a signal wire that is tapped into the compressors power wire to the other. That way once the temp gets too high the temp sensor would activate the first solenoid (you could even run two of them in parallel for a dual zone fridge so it would activate the solenoid if either one got too hot) that would give power to the inverter and ideally turn it on and give power to the fridge, which would activate the compressor and give power to the second solenoid and close it. Then as the temp drops the first solenoid would open, but the second would continue supplying power until the compressor shuts off due to the fridge being back down to temp according to the fridges built in temp sensing. The solenoids are designed to withstand a pretty high amount of current for a starter, but I would have to look up what the specs are. I’m not sure it would work on the compressor side though because I believe that gets 120v, definitely not 12... so it would likely need something a bit beefier...

Please let me know what you guys think, and if you have any ideas on where to source a solenoid or similar switch that would work on the high voltage side. My other concern is that a starter solenoid may not like the continuous current considering they’re normally closed for a short period to start the car and then open right back up. Finally, the only way for this to work is if you assume the inverter will allow you to turn it on and off just by disconnecting/reconnecting it when the switch is left on, or would you need to cycle the power switch? Please, all ideas and opinions are greatly appreciated.

thanks

ps. it would be much easier if there was a remote circuit which you could simply control with relays instead. Is that a thing? Or just a dream?

Edit: Turns out many inverters do have a remote circuit, and I figured out a cheap, easy way to take advantage of that to automatically turn on and off your inverter at a temperature of your choosing! See me the post after next and I'll explain it all and include (non-affiliate) links to parts.

 

[pollenface]

I've been running a 260L fridge directly from a 12v 2000w inverter for the past 6 months. It uses approx 700wh/24hrs.