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Old 07-13-2015, 11:53 AM   #1
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chest freezer as fridge

I've seen a few of these threads, but they're all pretty old, so I figured I'd start another.
I'd like to start out by saying that all of my experience with this is theoretical. Merely daydreams in front of a computer screen while reading someone else's blog. If I cross anyone who has actual experience, speak up. My intent is not to offend. Now that I've said that, onward.
While looking into high efficiency fridges that I could run off a battery bank, I stumbled across chest freezer conversions. It seems like a well-travelled route, and definitely just what I was looking for (if you've never heard of this, just google "chest freezer conversion", there are a few methods, and a whole lot of info out there).
Now, by far the most common conversion is done by using an additional thermostat, which cuts power to the whole freezer when the desired temp is reached (for a fridge it would be 32F-40F or so). This setup seems odd to me for several reasons: it requires an additional electrical gizmo, and the whole point of the conversion was to minimize electrical load; most people insert the temp sensor through the door seam, which creates an insulation breach and the potential for wasting energy; and the sensor needs to be positioned mid-depth in the freezer and away from the walls, which is prohibitive in stuffing it chock full (the most efficient way to use any fridge or freezer is when it's as full as possible, so you aren't cooling air, which has low thermal mass). Most people would probably say that these concerns are negligible, but I'm obsessive.
So, I went looking for a different option. I remembered that when I was a kid my dad taught me about "coarse adjustment" versus "fine adjustment" on these chest freezers, so I looked in that direction and found this article: Guide to set internal chest freezer thermostat to >32F; Eliminate external control - Home Brew Forums
Turns out you can adjust a bone stock chest freezer to act as a fridge using nothing but a screwdriver and some know-how. But, my thread here has two purposes. The first is to spread the word about a lesser known and cheaper method of achieving what a lot of people out there already have. The second is to ask someone who knows more about battery bank systems than me if this is, in fact, as efficient as it seems to be.
In both systems there is some amount of 24/7 draw. In one you have the freezer's circuitry, in the other you have the additional thermostat. Which draws fewer watts/day? Is the external temp controller more efficient than letting the freezer's circuitry run all the time? If so, is it enough better to make up for the potential thermal losses I pointed out?
I assume that these questions are impossible to answer without actually testing them. I only ask them in the off chance that someone actually has. After all, I'm sure I'm not the first person considering this route as an alternative.

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Old 07-13-2015, 12:25 PM   #2
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We did the thermo controller route a couple weeks ago. Ordered one from Amazon for about $15. It's not just a plug-in thing, so you have to know at least a little about wiring to be able to put it in. Luckily my dad knows some stuff. He helped install it and we tested it out. We have a large deep cycle marine battery and a 1100 watt inverter. With the freezer set to 35 degrees, a variance of 3 degrees and no compressor delay, with an empty freezer, the battery lasted somewhere between 2.5-3 days. The freezer is supposed to pull about 150w by itself, unmodified. I'm not sure of the cubic footage of the freezer, but it's about 35L"x32D"x25"W externally. Not the tiniest you can get. I can't remember the battery size at the moment, but I've been meaning to look. I can update this later.

I want to put a meter on it and see what it draws compared to pre-modification. Our battery is also a year old and may not have been maintained as it should have been.
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Old 07-13-2015, 09:44 PM   #3
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There is a fair amount of info online regarding this trick. Most I have read with follow ups seemed to be very pleased with the results.

Personally, I am going with a chest type freezer/fridge just because they don't "lose their cool" every time you open the door.
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Old 07-13-2015, 09:55 PM   #4
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Digital thermostats draw miniscule amounts of power. Mechanical draw none, but there is usually a light that draws more.

The main reason to do a digital one is to get a tighter control for less temperature swing. A fifteen degree swing isn't that much when you are talking zero to minus ten, but you don't have that much room to dance around 32-40
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Old 07-13-2015, 10:15 PM   #5
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@r_w, thanks! Is the circuitry in a freezer mechanical? And is the light you're talking about the small indicator on the control panel, or the interior light that illuminates when you open the door? Either of these could easily be disconnected. With the power cutoff method they wouldn't work most of the time anyway, so disconnecting them makes little difference.

Also, a fridge that is full can have significant swings in air temperature without changing the temperature of the food by much at all. Maybe a couple degrees, maybe even less. If you don't have enough food to fill the fridge, fill it with jugs of water to maintain a high thermal mass (however, it takes energy to get water down to temperature, so I strongly recommend buying a fridge that is sized small enough to fit only the things you need, this way you get high thermal mass per cubic foot without any redundancy). The less air in there, the more efficient, no matter what.

Don't take my word for it!

There's plenty of info about this on the link I mentioned earlier, and many other sources besides.

@Tango, I really like your short bus and it seems like a lot of others do as well. Maybe if you write a tidbit about this way of using a chest it will help get the word out about it. That is my main goal after all.

For anyone who's willing and already has a temp controller, I'd love to get a side-by-side comparison of the two techniques. I'm very interested in a watts/day analysis of each. All things being equal (eg. freezer model and internal/external temp ranges), the numbers will show whether buying/using a temp controller has merit.
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Old 07-14-2015, 07:43 AM   #6
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Yes, I was referring to the little indicator light.

The individual differences in motors and compressors will make a bigger difference in power requirements than the t stat. Many solar guys show a +/-10% variance between two of the same model running side by side.

If you really want to shave milliwatts, adjusting the hysteresis to limit short cycling of the compressor and super insulating the box are your low hanging fruit.

There are instructions out there on how to build your own box like in a yacht. Blue or pink foam, a little glue, some fiberglass, and a compressor and plate kit from a yacht supply. Yes it is more expensive because it has yacht in the name, but they do work on way less power and can be made to fit your hole. You can mount the compressor under the floor if you want. And you probably save enough power to money ahead by buying less batteries and panels.
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Old 07-14-2015, 07:59 AM   #7
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good info. +/- 10%?! Would never have guessed!
Building a custom box is definitely a goal. I'm hoping to figure out how to make myself a drawer-fridge in the distant future. For right now though, in the interest of getting my bus livable for cheap, I'm picking up a chest freezer on CL and adjusting the thermostat. I've seen good ones for $50, so I just need a little patience.

It'll be a significant improvement over my mini fridge, at the very least.
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Old 07-29-2015, 07:59 AM   #8
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I found a bunch of cool videos showing how to use a temperature controller for fermenting or sous vide.
I'm sure a lot of people have a cooler and a light bulb, and/or a crock pot. Now that you know that the chest freezer doesn't need a temperature controller to refrigerate, you can do other cool things with it.

https://www.youtube.com/watch?featur...&v=97zWWLRjfVw
https://www.youtube.com/watch?featur...&v=ZNLz814NvIw
https://www.youtube.com/watch?featur...&v=knkfb-67HU0
https://www.youtube.com/watch?featur...&v=glU77K-10hA
https://www.youtube.com/watch?featur...&v=R0cn2OmXxFU
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Old 07-29-2015, 10:32 AM   #9
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Ive been living with mine for a few weeks now and I love it. The extra t-stat I added is fully mechanical and doesnt use any power. I put a kill-a-watt on it and it draws nothing when off. The wire for it is TINY and I bet makes no noticeable difference in the effectiveness of the rubber seal. As for modifying the stock t-stat, I didnt see a clear easy way to on my freezer, but it was a brand-new unit so it might be a lil fancier.

As to digitial vs. mechanical--mine has been keeping my fridge at almost exactly the temp I set it with a variance of no more than at MOST 3 degrees. Its accurate and there's more temp difference top to bottom of the fridge than from the t-stat.
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Old 07-29-2015, 01:12 PM   #10
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Here's my brand new GE chest freezer. On the right you can see the cover for the "controls box", you'll need to take this cover off. On the left you can see the control panel with the temp adjustment knob. When I put this freezer in my bus I'll disconnect that green light, but the light inside the freezer (which wouldn't work with a temp controller) will stay, because I like to snack at night without needing a flashlight.



Here's what's inside the cover. You can see the thermostat on the backside of the temp adjustment knob, this is where you can do coarse adjustment to bring the temp up to refrigeration level.



To get a good picture of the coarse adjustment screw I had to pull out the control panel. It's only held in by a few tabs, so this is a very simple operation.



Here's the coarse adjustment screw, right on the side of the thermostat. It may be covered by a sticker, or some tape (like mine was). Who knows why the manufacturer obscures this screw, but that little piece of tape is probably the main reason that people have chosen to spend money on a temp controller as opposed to simply adjusting their stock thermostat.



Here's my nifty remote thermometer. When doing the coarse adjustment I put this inside the freezer so I could read the temp without opening the door, but any thermometer will work. It took me a few tries to get my temp right.
Attached Thumbnails
IMG_0125.jpg   IMG_0127.jpg   IMG_0128.jpg   IMG_0129.jpg   IMG_0130.jpg  

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Old 07-29-2015, 01:22 PM   #11
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Mmmmm...no pix for me. Anyone else?

PS...I am still going back & forth on the fridge/freezer issue. I don't have room for one of each but will need both so I've been looking at some over the counter units that combine the two. One is by Whynter and so far is the only 12v I've found that is a dual zone unit. Not cheap at $640 bucks (on "sale"). I may be able to build a super-insulated version from scratch, but this is a good model.

http://www.amazon.com/Whynter-FM-62D.../dp/B008VX01P2
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Old 07-29-2015, 01:30 PM   #12
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I think I fixed the pictures.

Quote:
I don't have room for one of each but will need both
I like that unit, but 2 cu ft is too small for me.

My theory is that you could make an insulated compartment at the bottom of your chest unit, which may get cold enough to act as a short-term freezer. I've never heard of it done before, but it's definitely something I'm going to try. My only immediate doubt is how the location of the stock thermostat might effect temps in the rest of the unit.
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Old 07-29-2015, 03:40 PM   #13
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PDBreske did two of these for his bus conversion. One he adjusted the thermostat on the freezer and the other he used a Johnson Controls thermostat.

Quote:
Originally Posted by PDBreske View Post
Got my new Johnson Controls thermostat controller today and used it to convert my chest freezer to a refrigerator:


The chest freezer is so efficient that it took a couple of hours for the temp to come up to the new set point for the A419 controller. Once this thing is filled with food and drinks, it should be even more efficient (the contents will add a certain amount of thermal inertia).
Quote:
Originally Posted by PDBreske View Post
I looked at a few different options for the thermostat controller, but found the Johnson Controls model had the most features. I like the "Anti Short Cycle Delay" that prevents the freezer/fridge from cycling too often and should help the compressor last a bit longer. I bought this freezer used on craigslist ($50) and the JC controller cost about $75 on Amazon, so my total cost for a chest refrigerator is a little less than a new freezer on sale. In fact, I saw this same model freezer on sale at Target for $127 and should have bought one to use as a freezer, but missed the opportunity. Still regularly scanning craigslist for another one.

Only one problem I had was closing the lid of the freezer with the wire for the thermocouple draped across the opening. The wire is about an eighth-of-an-inch thick and the lid and body of the chest are quite tightly sealed with matching rigid plastic parts and a rubber gasket. The plastic parts normally fit very close together and the wire was holding them open, creating a small gap even between the rubber gasket and chest body. The gap let in a little warm air and was causing formation of condensation around the opening, so I added a strip of soft weatherstripping to compensate. My freezer is an Emerson CF450, so this may not apply to other models or manufacturers.

I'm also going to place a bunch of jugs of water into the fridge to simulate a chest full of food and drinks and watch to see if this keeps the temperature a bit more stable inside.
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Old 09-19-2016, 07:19 PM   #14
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im thinking the same.

This looks like a good idea. Im thinking of doing the same just to shy away from a Propane RV unit. I see Sproutroot just turned his thermostat down internally. Has anyone else done this?
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Old 09-19-2016, 07:39 PM   #15
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We ran a chest fridge and freezer for about 5 years. A bit inconvenient in the grand scheme but miserly in the electrical realm.
For bus conversions running on a battery bank I would totally recommend them.

We could easily get 5 day run time with a 600 amp hr battery bank.

It's a no brainer if you want to stay away from a 3 way fridge and propane.
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Old 09-19-2016, 09:01 PM   #16
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What are some reasons to stay away from RV 2way or 3way units?

There's pretty much a endless supply of old RV parts on CL where I'm at. Retirement Capitol of the world
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Old 09-19-2016, 10:27 PM   #17
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Mostly because they are overpriced RV crap. They suck too much juice on electric...will freeze the coils up solid on propane if not perfectly level...and generally don't work worth a flip. Just my two cents. Anyone else?
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Old 09-19-2016, 10:42 PM   #18
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Ive no idea power useage on electric. I know the one in my motorhome uses very little LP, and the freezer will literally freeze Vodka into a slushee . From what i understand though, they are very expensive to fix as well (and i DO have to keep it VERY level). My current bus project is My "sample bus", so I am trying to keep thing modular so I can take them for my "refined bus" project... (once i figure out what works for me.)
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Old 09-19-2016, 10:57 PM   #19
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Quote:
Originally Posted by NowhereFast View Post
What are some reasons to stay away from RV 2way or 3way units?
Most RV fires begin in the propane refridge.
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Old 09-19-2016, 11:02 PM   #20
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Quote:
Originally Posted by Tango View Post
Mostly because they are overpriced RV crap. They suck too much juice on electric...will freeze the coils up solid on propane if not perfectly level...and generally don't work worth a flip. Just my two cents. Anyone else?
And they catch fire and burn your RV to a crisp. Just look at pictures of burnt RVs in junk yards - where do many of the fires start? Yup, the fridge vent area.

I'll also go the converted freezer route when the time comes. I'm thinking of buying two small chest freezers and using one as a fridger and the other as a freezer, then I'll have the best of both worlds. I've got plenty of power to run them both (2kW of solar on the roof!), and I could run them from a small cheapo second inverter like an Exeltech XP-1100, or maybe a small Samlex or Cotek for each. (If you have more than one Cotek, are they then Kotex?)

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