Idea for shutting off inverter when fridge is not running.

YamInaBox

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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.
 
Last edited:

Hedges

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It is an idea I like too, but not for my present setup because I power the whole house, don't need the high efficiency for a small system.

1) Starter solenoids aren't designed for continuous duty, likely to burn up. Need an "economizer", high current to close, small current to hold.
2) Cycling power to inverter means repeated surge current charging caps. Something may fail. Solenoid/relay would at least need a snubber to extend its life.

Better if inverter has remote enable switch. Or sleep mode.

Turning off at night is another of my ideas. Less battery needed. During the day, PV is cheap.
Could have an additional thermostat to override and turn back on if really too warm.
 

Short_Shot

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Your fridge's controller may not appreciate the repeated power loss as well.

They're definitely not designed for it at any rate.
 

Bud Martin

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Using remote on/off terminals is better than cutting off DC feeding the inverter DC input.
 

YamInaBox

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Yeah, I'm starting to feel a bit of a fool right now. I was thinking about this while I was at work and made a post real quick about it on my 10, but I just got home and looked up "inverter remote shut off" on you tube, and the very first video is a guy talking about doing the same thing with the solenoids. But his inverter has an after market option for a remote shut off switch that works with a phone line plug + wire. By connecting 2 of the 4 wires of the chord it turned on the unit and when they disconnected the inverter shut off. So this would be a much better otion. Also apparently the guy looked into sourcing solenoids before the video because he commented that the ones rated for the amount of current he would pull with his 1500w inverter were pretty expensive. But that makes me curious if I couldn't figure out a way to avoid tapping into the compressor circuit, because I believe the high voltage may still cause me some problems. The guy in the video simply installed a switch inside because his inverter, batteries, and all that were stored outside. I would like to make it automatic so I can get one large inverter to run everything off of without having to worry too much about the idle draw instead of getting a smaller dedicated inverter to run the fridge continuous, therefore saving me not only power, but a decent amount of cash. I should be able to find a 120v relay, right? That would greatly simplify it because I wouldn't have to use massive wires and all that, then I can add a third parallel circuit with a simple switch so when I want the inverter to stay on, I simply flip on the switch. (unless the switch on the front of the unit would negate the remote switch when it's in the on position. if that were the case, then my switch is already there) Sorry for rambling on about this, my brain is stuck on it, and the worst part is, I don't even have an inverter yet, so what am I doing. I suppose that's the point, I'm trying to figure out what I need to get. Anyway, thanks for the advice. Cheers.
 

YamInaBox

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I like this idea.
Thank You. My brain won't leave it alone, I've been obsessing about it all afternoon. I found a couple pretty cool 120v relays on amazon. They have relays that do all kinds of things its actually really cool. However, it just dawned on me, that the way a simple old school battery operated thermostat (like for HVAC) works: it has a thermistor for ambient temperature, which then closes a switch at the appropriate temp. Unfortunately, after reading through some manuals, they don't seem to go any lower than 50 degrees F. However, that lead me to simply search amazon for "programmable temperature switch" which lead me to this little beauty right here:


You can set it to heating or cooling, aka starting low and ending high, or starting high and ending low, which is exactly what we need, and only $12 for two of them!!! It couldn't be more perfect. The temp range is -50c to 110c accurate within 0.1c! If your inverter switch works the same way as the fella in the video I watched, (His had a telephone wire plug. Cut and strip an old phone line and plug it in to the inverter while it is switched off. There are 4 wires inside, simply touch pairs together one at a time until the inverter kicks on to find which ones are the remote. He said his were the first two wires in the plug. Make sure to mark them so you remember which ones to use) it doesn't require power, just simple continuity. Although, this temp module needs 12v power to run, and in turn will output 12v, so you'll need to get a relay so you don't burn out the inverter remote switch by putting power through it. You can use pretty much anything 12v, like these ones for example:


It's a 5 pack, but it comes with the wiring harnesses for them so you can just crimp and go, and I didn't look long enough to find one being sold individually that was a decent price but these are only $10. Who couldn't use a few extra relays lying around? They're 30amp I believe so you can use them for all kinds of stuff. Or just go pull one out of basically any car at the junkyard, forget it's in your pocket, and you'll wind up at home with a perfectly free relay!

The wiring for this setup is super simple too. First, connect the black and yellow wires to terminals 85 and 86 of the replays listed above, (other relays may be labeled differently, I'm not sure) you can do this interchangeably, it doesn't matter which wire goes to which. Second, attach the remote switch wires coming from the inverter phone plug to 30 and 87 (not 87a, it will end up working the opposite way you want, in fact it probably wouldn't turn off) and again, it doesn't matter which way you put them. Tip: The phone chord wires are generally very small, strip back extra insolation and fold the wires back on themselves once or twice and twist them together to give you more surface area for the crimp connector to grab onto. Finally, connect the module's red and black wires to your fuse box, these are directional, red is positive and black is negative. Alternatively, they can be connected straight to the battery with an inline fuse. (kinda a different way of saying the same thing, haha) If you want to make life easy for yourself, add in a jumper wire with a switch in the middle of it while you're crimping the remote wires to terminals 30 and 87, this will allow you to bypass the temperature module and keep the inverter on when you need to use it for other things as well, so use an appropriate length of wire to mount the switch somewhere accessible. (Disclaimer #1: As I said earlier, this wiring is dependent on how the remote switch for your inverter works. This is assuming it's based on continuity like others I've seen. If not, you may need to take a slightly different approach, but you should be able to use the same parts. Disclaimer #2: I unfortunately do not have any of my equipment yet because I am currently in the process of planning out my system, so I have not been able to test to functionality of this circuit or any of it's parts. That being said, correct me if I'm wrong, but theoretically it all seems to check out and I do plan on doing this when I get up and running. Until then, I am unable to guaranty anything, but I really do believe it should work just fine and make people happy. I just wanted to be up front about that.

After you get it all set up, I would leave the switch on and use the readout on the module and record what temperature the compressor is turning on and off at for your desired settings in normal operating conditions. I also recommend having the sensor reading the fridge temp if you have dual zones considering the fridge temp is most likely going to fluctuate faster and more often than the freezer, unless you wire the second temp module parallel to the first one by crimping them together at the relay terminals, then you can use one for fridge and one for freezer, and either one will turn on the power until the desired temp is reached. Personally, that seems a little pointless/overkill and I will probably only monitor the fridge temp and save my second one as a backup or use it on another project. Anyway, once you decide on your start/stop temps all you have to do is program them into the module and your fridge should essentially work the same way it does when it's plugged in! You could even stretch the temperature difference a little bit by letting it get a little warmer before turning on, and possibly save a little more juice. It would be interesting to see what kind of results would come from that. There probably wouldn't be too much savings before it starts to go the other way from having to work harder to compensate for the extra heat, so you're probably better off just going with the recorded temps, at least to start. It was just a thought.

That's it! A $20 power saving fridge/inverter hack that probably only took 10 min! Now you no longer have to worry about currant draw from an unused inverter that's just waiting for the fridge to cycle back on! Also I can rest easy about buying a single high output inverter to run everything I need instead of wasting money on a dedicated lower wattage/lower draw inverter just for the fridge. It's funny now how complicated I was making it to begin with, it's like they say, Keep It Simple Stupid. One module, One relay, One switch -> Hundreds of watt/hours saved! I should make a video demonstrating this, I bet I'd go viral haha, too bad I don't have any of the equipment yet...

What do you think? Should I cut this down and repost the final instructions in the general discussion tab or something? I might draw up a little wiring diagram and post a picture of it, but it's really pretty simple and I think I explained it pretty well for anyone who couldn't figure it out on their own. Anyway, I hope this helps, and please let me know if you end up installing these parts or something similar/different. Maybe my brain can finally rest easy now that it has established a solution. Cheers.
 
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Steve_S

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Why not use KISS and not get complicated for no reason ?
Most Inverters have a PowerSave mode, which essentially puts; them into Standby (very low power draw) when there is no demand. The inverter sends low-volt Pulses every few seconds to "sense" for demand, if there is enough demand that activates the Inverter, provides the required power and then back to powersave when done.

Typically such requires between 8-10W demand on the VAC Line to activate the Inverter (They vary and not all have PowerSave / Sleep Modes).
The "Pulse" will make LED Lights "Blink" and appliance digital displays will blink like there was a power loss.

More complicated things get the more likely something will go awry and result in Angst at best.
 

Hedges

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Your fridge's controller may not appreciate the repeated power loss as well.

They're definitely not designed for it at any rate.

"May not", as you say. If it is an inverter drive or otherwise has electronics.

However, if just a basic refrigerator/freezer where controller is nothing more than an electromechanical thermostat (bimetalic strip and switch), all it ever does is turn power on and off. There is also a timer motor that switches between compressor and defrost heater. In that case, turning off AC power is no harm. (What you don't want to do is turn off compressor and turn back on in a short time, before pressure has bled off.)



Why not use KISS and not get complicated for no reason ?
Most Inverters have a PowerSave mode, which essentially puts; them into Standby (very low power draw) when there is no demand.

My inverter draws 25W at no-load, 6W standby, so this would save 75% of the 600 Wh/day it would consume always being on (reduce savings by the percentage of time refrigerator needs to be powered.)

Without using standby mode, would need an extra 100W or 200W PV to supply the wasted power.

But I think shutting off at night to reduce needed battery capacity would be useful. If a refrigerator consumes 1200 Wh/day, about 600 Wh of that has to come from battery at night. Keeping inverter shut off at night (or in standby) reduces draw by 50 Ah or so for a 12V system.

Given a remote port in the inverter, it could be turned off. Without that, an appliance timer or "on at dawn, off at dusk" light sensor would keep it from running at night. If it does get too warm I would want it to turn back on. That's where a second thermostat bypassing timer (or light sensor) would help.
 

YamInaBox

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Why not use KISS and not get complicated for no reason ?
Most Inverters have a PowerSave mode, which essentially puts; them into Standby (very low power draw) when there is no demand. The inverter sends low-volt Pulses every few seconds to "sense" for demand, if there is enough demand that activates the Inverter, provides the required power and then back to powersave when done.

Typically such requires between 8-10W demand on the VAC Line to activate the Inverter (They vary and not all have PowerSave / Sleep Modes).
The "Pulse" will make LED Lights "Blink" and appliance digital displays will blink like there was a power loss.

More complicated things get the more likely something will go awry and result in Angst at best.
Yeah, there are power save modes, but a lot of inverters I've seen still pull quite a bit of power. Like the Giandel 4000w I've been considering, it pulls 36w (3a) with no loads. Maybe that isn't HUGE, but it adds up. I'm building out a box truck home and don't want to pay for any fuel other than gas in the truck, which is expensive enough as it is. That means I need to cook and everything else with the power I generate and store. So every bit counts in my opinion. And to be honest, it's such a cheap, simple circuit, why wouldn't you want to add it and save 36watts? And if all that blinking and whatnot you're talking about is a result of the power save function, it seems a lot more finicky and unstable than a programable on/off switch. From my experience, things aren't that complicated if you know what you're doing, and they tend to turn out just fine when you do them right.

This little circuit is so simple to make, and literally acts the same as you standing at the remote switch of your inverter and turning it on practically the exact moment your fridge needs power again, and then turning it back off when its done, and repeating that process automatically all day long in order to save power. I don't really understand what you think is so complicated about it. It's merely adding two very basic components that cost less than $20 combined and even come with backup replacements at that price! What I was proposing in my initial post was complicated, but that was just brainstorming, a necessary part of the creative process, and personally I'm pretty happy with what it ended up yielding in this particular case.

Regardless, thanks for your opinion, man
 

Short_Shot

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Well.


6w standby is 144wh a day. And presumably you are actually using the inverter part of the day so it'll be less than that to make up for.
Given my results with my 50 watt of panels on my tongue box you could make up for that with much, much less than 100 or 200 watts of extra panel. My lead battery in my driveway is at float every day for about 4 hours with about 30-40w of charge and it's roughly 110 wh needed to do so (there is a GPS tracker in that trailer). It would definitely handle 144wh with just 50w extra stuck somewhere. See attached.

Of course that implies you have enough battery to burn on it. Shutting off a fridge at night makes sense if you are overpaneled and can afford the extra long run time on the compressor every morning, but can't spare the battery at night, AND the thing stays cold overnight.

As for what you will save shutting it off if you DO have extra battery to spare, you'll save a bit of power on average but not likely not anywhere 50ah a day. Usually it's more economical on power to keep it going because you're not picking up all that extra heat at night that it'll need to chill down again in the morning. That's time it'll have to run at full load to come back down depending on how it's designed and how efficient it is.

My iceco for example takes about an hour to go from 45 to 35 degrees when it's full. And it's tiny. Only 42 liters.

Also if your fridge is pulling 1.2kwh a day it must be a big fridge or there's something wrong with it. The one in my kitchen at home pulls that much and it's a French door with icemaker and bottom freezer, so not very efficient to begin with. I just had it on a killawatt recently.

If it's a large unit then it may take much more than you might think to maintain a certain maximum temperature overnight, and from a food safety standpoint this number is 40F as a worst case, and then a fair amount of constant running during the morning to get back down to 36 or 37F where most fridges run at.

If you're running it up to 45 degrees you risk problems with your food, but that depends on the food in question of course.


So if done carefully, you can come out on top, but without enough data and testing these run conditions you can't really be sure. You might be spending extra money for nowhere near what you think you're going to save.
 

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YamInaBox

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"May not", as you say. If it is an inverter drive or otherwise has electronics.

However, if just a basic refrigerator/freezer where controller is nothing more than an electromechanical thermostat (bimetalic strip and switch), all it ever does is turn power on and off. There is also a timer motor that switches between compressor and defrost heater. In that case, turning off AC power is no harm. (What you don't want to do is turn off compressor and turn back on in a short time, before pressure has bled off.)





My inverter draws 25W at no-load, 6W standby, so this would save 75% of the 600 Wh/day it would consume always being on (reduce savings by the percentage of time refrigerator needs to be powered.)

Without using standby mode, would need an extra 100W or 200W PV to supply the wasted power.

But I think shutting off at night to reduce needed battery capacity would be useful. If a refrigerator consumes 1200 Wh/day, about 600 Wh of that has to come from battery at night. Keeping inverter shut off at night (or in standby) reduces draw by 50 Ah or so for a 12V system.

Given a remote port in the inverter, it could be turned off. Without that, an appliance timer or "on at dawn, off at dusk" light sensor would keep it from running at night. If it does get too warm I would want it to turn back on. That's where a second thermostat bypassing timer (or light sensor) would help.
Yeah, I was about to give up on the idea before I learned how the remote switch could be utilized. But yeah, the potential power savings really adds up and could make 120v fridges a much more reasonable/practical option. The cost savings alone, not to mention all the extra storage. Just as long as you have the room in your rig. (but then again, they keep getting more efficient and they make some that are so small that it could really work for anyone with even as little as 100w of efficient solar)

That's a pretty cool idea. I was also thinking about turning it off at night, just manually (at least in the winter) but when you mention using a temp sensor to ensure it doesn't get too warm that makes sense because you obviously won't be able to monitor it in your sleep, and it would put the extra temp sensor to good use. You would just have to make sure it was a decent light sensor in a strategic location, you wouldn't want your fridge shutting off all day because it had too much of a shadow or maybe a leaf or something landed on it. Also, you don't want it to get contaminated by your lights, streetlights, or even a bright enough full moon (I honestly wonder if the moon could trigger it, cuz I've seen some pretty damn bright moons , but probably not...) Overall I think a timer would be your best bet for that. I saw some 120v timer relays on amazon but I'm not sure if it would work for this because we're turning the 120 off. Honestly I'm not even really sure how they work, there wasn't much of a description for them.

But then again It really depends how long the fridge stays cold on its own, it might be pointless if it heats up consistently before your timer goes off, you could just program a higher temp on the one circuit. It all depends, like I was saying about the experimenting with the temps, you might save power to a certain extent before the fridge ends up using too much power to get it cold again. I can't wait to get everything together so I can experiment with it.
 

Short_Shot

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The only problem i see with the higher night temp allowance is the temperature at which its no longer "food safe" is only a few degrees higher than what most people consider a cold fridge.
 

Hedges

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Of course that implies you have enough battery to burn on it. Shutting off a fridge at night makes sense if you are overpaneled and can afford the extra long run time on the compressor every morning, but can't spare the battery at night, AND the thing stays cold overnight.

A refrigerator/freezer is going to consume enough power to match what leaks out through insulation (plus inefficiency of compressor system.)
I don't think cooling it back down after the sun comes up uses any more power than cycling a couple times at night. But I've never run the experiment. Benefit is it would draw from PV rather than draining battery. (Due to relative cost of PV vs. battery and their lifespans, I prefer to over-panel and minimize battery.)

We do want to maintain proper temperature. Top or side freezer will keep refrigerator relatively cool but freezer warms up linearly until something goes through a phase change. H2O would do that phase change at 32 degrees F. H2O + NaCl could be tuned to do that at a temperature which kept frozen foods solid.


The only problem i see with the higher night temp allowance is the temperature at which its no longer "food safe" is only a few degrees higher than what most people consider a cold fridge.

That refers to fridge not freezer, so a simple experiment. Put a thermocouple inside fridge, unplug, and log temperature vs. time. Needs to be a time when room is hot to get worst case. Could be that so long as freezer has ice, fridge stays safe. That depends on air circulation. My side-by-side has a fan to force air through freezer, a 1" hole at bottom and a 3" hole with baffle at top. Fridge is cooled by convection, but the forced air in freezer (and colder air when compressor running) probably increases cooling of fridge.

I turned that side-by-side into all-freezer by simply changing thermostat and removing baffle. Both sides stay quite cold, but took longer to freeze the "refrigerator" side.
 

YamInaBox

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Well.


6w standby is 144wh a day. And presumably you are actually using the inverter part of the day so it'll be less than that to make up for.
Given my results with my 50 watt of panels on my tongue box you could make up for that with much, much less than 100 or 200 watts of extra panel. My lead battery in my driveway is at float every day for about 4 hours with about 30-40w of charge and it's roughly 110 wh needed to do so (there is a GPS tracker in that trailer). It would definitely handle 144wh with just 50w extra stuck somewhere. See attached.

Of course that implies you have enough battery to burn on it. Shutting off a fridge at night makes sense if you are overpaneled and can afford the extra long run time on the compressor every morning, but can't spare the battery at night, AND the thing stays cold overnight.

As for what you will save shutting it off if you DO have extra battery to spare, you'll save a bit of power on average but not likely not anywhere 50ah a day. Usually it's more economical on power to keep it going because you're not picking up all that extra heat at night that it'll need to chill down again in the morning. That's time it'll have to run at full load to come back down depending on how it's designed and how efficient it is.

My iceco for example takes about an hour to go from 45 to 35 degrees when it's full. And it's tiny. Only 42 liters.

Also if your fridge is pulling 1.2kwh a day it must be a big fridge or there's something wrong with it. The one in my kitchen at home pulls that much and it's a French door with icemaker and bottom freezer, so not very efficient to begin with. I just had it on a killawatt recently.

If it's a large unit then it may take much more than you might think to maintain a certain maximum temperature overnight, and from a food safety standpoint this number is 40F as a worst case, and then a fair amount of constant running during the morning to get back down to 36 or 37F where most fridges run at.

If you're running it up to 45 degrees you risk problems with your food, but that depends on the food in question of course.


So if done carefully, you can come out on top, but without enough data and testing these run conditions you can't really be sure. You might be spending extra money for nowhere near what you think you're going to
Yeah, it may not be a ton of savings, but it can add up if you're array is limited and you're not getting full sun days, like especially with mobile setups. Iceco fridges are really nice, I would love to have one, but to be honest I'd rather spend the extra money one solar and batteries and just get a far cheaper dorm style fridge. With the extra savings it wouldn't take much to compensate the difference in power either.

I agree with the turning off too long, I mentioned that when I was talking about experimenting with the temp in the initial post when I figured it out. You could probably let the temp rise a little and maybe get a slight savings, but after too much you're fridge is just going to eat it back up. Also food safety is important, I wouldn't want to get food poisoning while living in a van with no flush toilet, that just sounds like a bad time! But if it were just drinks, it wouldn't really matter and the freezer would probably be okay as long as you keep it closed.
 

Hedges

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That's a pretty cool idea. I was also thinking about turning it off at night, just manually (at least in the winter) but when you mention using a temp sensor to ensure it doesn't get too warm that makes sense because you obviously won't be able to monitor it in your sleep, and it would put the extra temp sensor to good use. You would just have to make sure it was a decent light sensor in a strategic location, you wouldn't want your fridge shutting off all day because it had too much of a shadow or maybe a leaf or something landed on it.


This HF timer has a rechargeable battery. After it has been plugged in for a while, it keeps its clock running even during power outages. This could turn your fridge off at night.

You could splice a thermostat to bypass the timer, re-enable fridge if temperature rises above a higher setpoint during the night.
Just make sure you don't make a "suicide cord" where the thermostat causes pins of plug that fits in timer to be hot. Either tape plug in to prevent removal, or look for a thermostat with SPDT switch so when it takes power from wall bypassing timer, it doesn't also feed power back to plug in timer.
 

YamInaBox

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That refers to fridge not freezer, so a simple experiment. Put a thermocouple inside fridge, unplug, and log temperature vs. time. Needs to be a time when room is hot to get worst case. Could be that so long as freezer has ice, fridge stays safe. That depends on air circulation. My side-by-side has a fan to force air through freezer, a 1" hole at bottom and a 3" hole with baffle at top. Fridge is cooled by convection, but the forced air in freezer (and colder air when compressor running) probably increases cooling of fridge.

I turned that side-by-side into all-freezer by simply changing thermostat and removing baffle. Both sides stay quite cold, but took longer to freeze the "refrigerator" side.
Is it a 12v or 120v? I think that makes a big difference. Comparing the two doesn't really make sense. I believe Short_shot was saying his 12v takes an hour to drop 10 degrees, but a small to mid size 120v fridge doesn't take anywhere near that long... And I'm not sure but I might speculate that it could take less overall energy too. Those 12vs are so efficient because you're keeping them cold and just maintaining that temp, In a cool down test I would think the 120v might win efficiency, even factoring in the inverter loss of 10-15%
 

Short_Shot

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A refrigerator/freezer is going to consume enough power to match what leaks out through insulation (plus inefficiency of compressor system.)
I don't think cooling it back down after the sun comes up uses any more power than cycling a couple times at night. But I've never run the experiment. Benefit is it would draw from PV rather than draining battery. (Due to relative cost of PV vs. battery and their lifespans, I prefer to over-panel and minimize battery.)

We do want to maintain proper temperature. Top or side freezer will keep refrigerator relatively cool but freezer warms up linearly until something goes through a phase change. H2O would do that phase change at 32 degrees F. H2O + NaCl could be tuned to do that at a temperature which kept frozen foods solid.




That refers to fridge not freezer, so a simple experiment. Put a thermocouple inside fridge, unplug, and log temperature vs. time. Needs to be a time when room is hot to get worst case. Could be that so long as freezer has ice, fridge stays safe. That depends on air circulation. My side-by-side has a fan to force air through freezer, a 1" hole at bottom and a 3" hole with baffle at top. Fridge is cooled by convection, but the forced air in freezer (and colder air when compressor running) probably increases cooling of fridge.

I turned that side-by-side into all-freezer by simply changing thermostat and removing baffle. Both sides stay quite cold, but took longer to freeze the "refrigerator" side.
It won't necessarily use more power, but you really won't save much either. Total heat in and out over time will still be basically the same.

You're not far off with the panel vs battery thing, and while you're right about the freezer, that's also why I'm not concerned about that aspect of it.

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.
 

Short_Shot

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Is it a 12v or 120v? I think that makes a big difference. Comparing the two doesn't really make sense. I believe Short_shot was saying his 12v takes an hour to drop 10 degrees, but a small to mid size 120v fridge doesn't take anywhere near that long... And I'm not sure but I might speculate that it could take less overall energy too. Those 12vs are so efficient because you're keeping them cold and just maintaining that temp, In a cool down test I would think the 120v might win efficiency, even factoring in the inverter loss of 10-15%
I did say that. But if his fridge is using 1.2kwh a day it can't be very efficient, and as a result may also take some time to come down.

You'd be surprised at how much time it takes to cool down even a big 120v modern fridge.
 

YamInaBox

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Aug 5, 2021
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This HF timer has a rechargeable battery. After it has been plugged in for a while, it keeps its clock running even during power outages. This could turn your fridge off at night.

You could splice a thermostat to bypass the timer, re-enable fridge if temperature rises above a higher setpoint during the night.
Just make sure you don't make a "suicide cord" where the thermostat causes pins of plug that fits in timer to be hot. Either tape plug in to prevent removal, or look for a thermostat with SPDT switch so when it takes power from wall bypassing timer, it doesn't also feed power back to plug in timer.
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...
 
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