3.5 cu. ft. chest freezer with thermostat as a refrigerator
YostFMX
Solar Expert Posts: 94 ✭✭✭
So after looking at all the small refrigerators and it seems they are all junk and don't work well and break I think I open to a chest freezer. I found that home depot sell a Magic Chef 3.5 cu. ft. chest freezer that is 219 kWh per year. It has a thermostat on the out side of the unit. So If I trun it way down to like 1 or 2 would that be the same thing as a "chest freezer conversion"?
My thinking is that it would be a good little frige thats would use probably under 150 kWh per year...
Is this right? or is a "chest freezer conversion" something other then just a thermostat?
My thinking is that it would be a good little frige thats would use probably under 150 kWh per year...
Is this right? or is a "chest freezer conversion" something other then just a thermostat?
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Generally, you need to add a separate thermostat that will work/cycle in the refrigerator temperature range. If you choose an electronic controller--you can have very precise temperature control (get near 32F with out freezing your stuff).
You will probably want to add a glued on plastic "gutter" around the inside of the "fridge" and direct the water to a tube out the base drain as it will condense water and probably puddle in the bottom.
Also--you may want a small computer fan to stir the air to prevent temperature stratification (warm at top, cold at bottom). Others have found an added fan is not needed.
Here is a good thread to read through:
Chest freezer as a chest refrigerator
If you cannot find a good temperature controller-- A McMaster-Carr, or Grainger Industrial Supply might be a good place to start.
-Bill
So you say it wouldn't go to a low enough temp with the thermostat thats on the unit then?
Typically, the freezer thermostat will not go warm enough.
Also, sometimes they don't work very accurately at that end of the range (you want to fridge somewhere between 33F and 40F (you may not find a setting that stays above 33F and does not go above 40F)...
A freezer that is set for 0F and cycles +/- 5F is not a problem. A thermostat set for 37F that cycles from 32-43 is probably not desirable.
I assume you will be running this off an inverter... You will probably want to pick an inverter with a DC inhibit input so you can cycle the inverter on and off with the thermostat mechanical and save the ~6-8 watts of stand by power. Or you can pick a DC powered temperature controller (low power draw) and cycle the AC or DC (you can use an inverter that has a search mode that only draws more power when there is a >8 watt AC load)...
-Bill
Ok, now my head is spinning...
I have no clue what your talking about with AC / DC stuff. I will be running a 110 AC freezer with a *True* sinewave inverter (off 12V DC), I don't think it has what ever you said with that power hibernate? Haha I want to do this as easy as I can (so I can undersand it)
From what I read you run your splice thermostat into the AC power cord? That don't seem right?
Yes, one way to do this is to splice a refrigerator replacement (you might get one from a local appliance store) into the AC line.
The issue is the "standby power" of the TSW inverter... 6-8 watts is typical:
- 8 watts * 24 hours = 192 Watt*Hours per day
Your "freezer conversion" may take as little as 250 Watt*Hours per day--so just the standby power on the inverter can be significant--unless you have other uses for the power.The Morning Star 300 watt TSW inverter (600 watt surge) (I am not sure it is big enough to start the freezer compressor), for example has a 55 mAmp standby setting:
- 0.050 Amps * 12 volts = 0.6 watts
- 0.6 watts * 24 hours per day = 14.4 Watt*Hours per day standby losses
Much better.You could also use a 12 volt relay to turn on the inverter's DC input power instead--but you are talking about a pretty big relay (possibly 100 amp)--which is an issue in itself.
The SureSine (for example) also has a simple electrical control line where you can "turn the inverter on/off with a simple switch--you could control the inverter with the fridge thermostat (if your inverter brand/model had a "remote on/off" input).
The original project appeared to use a digital control--perhaps a heater/AC control for a home (with latching relay). Unsolder the thermistor and add a thin set of wires to it and move into the fridge. The AC relay is good for 5 amp at 120 VAC--Perhaps to control the inverter remote control or add a second AC relay to handle the fridge starting loads directly...
Or, a simple mechanical one for $60. Plug it into the inverter and plug the fridge into the piggy backed cord.
By the way--I am guessing that you cannot set your "Freezer Thermostat" to refrigerate--just has been my experience when I tried that years ago...
-Bill
Hmmm, My home digital thermostat only goes to 45F--not quite low enough... Still trying to find a good battery powered digital thermostat.
Here is a nice 9-18v digital thermostat that will switch AC loads--$90
Hmm... The fridge may not last you a life time--but I would hope the controller does.
-Bill
Thanks! The simple one for $60 is what I'm looking for. Oh, so does it just work by cuting the power when it hits the temp? If so that sounds hard on the refrigerator... If not wondering how it can control the temp just on the power in line.
Sorry for all the questions, electrical is not my thing.
Edit_____________________
Heres the inverter I just orders last night: XANTREX-PROWATT-SW600-600-WATT-TRUE-SINEWAVE-INVERTER
I know its not really for solar... but I can't pay $275 +
Yep, you just set the "freezer dial" to a low temperature. And the external controller turns on the AC power to cool, and when the temperature set point is reached--it turns off.
Basically, the same way the freezer's mechanical thermostat works.
-Bill
Refrigerators and freezers have different refrigeration components, IE. compressors, condensers, evaporators, and metering devices. These components are selected for certain temp. range operation.
The compressors and components are designed to operate within a certain range:
Refrigerators 35 - 45 degrees
Freezers- -10 to +10
A lot has to do with design of the compressor, cylinder displacement, & motor windings. Hermetic compressors utilize suction cooling (cool refrigerant returning back to the compressor to cool the motor windings) at higher temps there may be insufficient cool refrigerant returning to keep the compressor within it's temperature operating range.
At higher temperatures the compressors may draw amperage over what they are rated for, that's OK for short term conditions, but to subject the compressor to operating conditions out of it's range will shorten the lifespan of the compressor.
So in short it's not a good idea freezers are designed as freezers it a lot more than just the thermostat used or the setting.
Can anyone comfirm this?
I know there are people in here that have done "chest freezer conversion" and I've never heard anything bad about them?
Personally, I would not worry very much about it...
The fridge conversion runs for very few minutes per hour... Assume 120 watt freezer running 250 Watt*hours per day total energy usage:
- 250 WH per day / 120 watts = 2 hours
- 2 hours * 1/24 * 60 min = 5 minutes an hour (on average)
Plus, every freezer is plugged in when new (and warm inside)--Plus anytime somebody puts a load of non-frozen food in the freezer--it has to run for hours to draw off all the heat...Lastly, the cost of a small freezer/fridge is low--If there was any long term life issue--the fact that you are consuming 1/4 the power of a full sized fridge--you are saving money on solar panels and battery (+ battery replacement) that would be required to run the more power hungry version of the appliance.
-Bill
Just went and checked some chest freezers and start up on a 5.0 chest freezer was 12 AMPS! Thats 1,440 watts. Thats nuts... any brands that have a lower start up AMPs? If not I'm going to have to take back my 600/1200 watt inverter.
What I've found is the smaller units, being small, do not have good tech put into them. The guys that make this stuff put the good stuff in the large, expensive units but put the 1950s tech crap into the cheap seats. What's worse, because the profit margin is not that great on the smaller units, there's only one, maybe two companies that make them all so they are the same unit across all manufacturers. If you find any major make with a small unit, it was actually made by the same company, and is the same unit, as the bargain brand.
Plus, it's easier to use a larger unit than a smaller unit. I picked up a 6 cu ft freezer to replace my 15 cu ft one when the kids moved out, figuring it would be enough for 2 people. I didn't realize at the time that the smaller shelves mean a much larger percentage of the room is needed to store a ham. Where before a ham left enough room around it to stack stuff on and around the ham, now there's not really enough room to do that so I have less usable room.
Check on a larger chest freezer, you might find that the larger units are more efficient in actual power usage than the tiny ones. You might also see if you can find a 12V unit anywhere, which would eliminate the need for an inverter. No idea on that though, most of the 12V market is going to be RVers and they aren't known for needing deep freezes.