Reply
 
Thread Tools Display Modes
 
Old 07-13-2015, 11:53 AM   #1
Almost There
 
Join Date: Jul 2015
Location: Vermont
Posts: 91
Year: 1996
Coachwork: Turtle Top
Chassis: E-Super Duty
Engine: Ford 7.3 Powerstroke
Rated Cap: 13-passenger
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.
sproutroot is offline   Reply With Quote
Old 07-13-2015, 12:25 PM   #2
Bus Nut
 
onenationundergoat's Avatar
 
Join Date: Mar 2015
Location: Statesville, North Carolina
Posts: 458
Year: 1993
Chassis: Thomas
Engine: International Navistar DT360
Rated Cap: 60
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.
__________________
My build thread:http://www.skoolie.net/forums/f11/build-thread-for-haulin-oats-and-goats-11237.html#post113500
A gal, a guy, three cats, two dogs, one rabbit, and one goat, traveling the country together.
onenationundergoat is offline   Reply With Quote
Old 07-13-2015, 09:44 PM   #3
Bus Geek
 
Tango's Avatar
 
Join Date: Mar 2011
Location: Houston, Texas
Posts: 5,589
Year: 1946
Coachwork: Chevrolet/Wayne
Chassis: 1- 1/2 ton
Engine: Cummins 4BT
Rated Cap: 15
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.
Tango is offline   Reply With Quote
Old 07-13-2015, 09:55 PM   #4
r_w
Skoolie
 
Join Date: Aug 2014
Posts: 160
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
r_w is offline   Reply With Quote
Old 07-13-2015, 10:15 PM   #5
Almost There
 
Join Date: Jul 2015
Location: Vermont
Posts: 91
Year: 1996
Coachwork: Turtle Top
Chassis: E-Super Duty
Engine: Ford 7.3 Powerstroke
Rated Cap: 13-passenger
@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.
sproutroot is offline   Reply With Quote
Old 07-14-2015, 07:43 AM   #6
r_w
Skoolie
 
Join Date: Aug 2014
Posts: 160
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.
r_w is offline   Reply With Quote
Old 07-14-2015, 07:59 AM   #7
Almost There
 
Join Date: Jul 2015
Location: Vermont
Posts: 91
Year: 1996
Coachwork: Turtle Top
Chassis: E-Super Duty
Engine: Ford 7.3 Powerstroke
Rated Cap: 13-passenger
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.
sproutroot is offline   Reply With Quote
Old 07-29-2015, 07:59 AM   #8
Almost There
 
Join Date: Jul 2015
Location: Vermont
Posts: 91
Year: 1996
Coachwork: Turtle Top
Chassis: E-Super Duty
Engine: Ford 7.3 Powerstroke
Rated Cap: 13-passenger
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
sproutroot is offline   Reply With Quote
Old 07-29-2015, 10:32 AM   #9
Bus Nut
 
charles_m's Avatar
 
Join Date: Sep 2013
Location: Denver
Posts: 489
Year: 1982
Coachwork: Blue Bird
Chassis: International S1800
Engine: DT466 Trans: MT643
Rated Cap: 65
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.
__________________
Patina enthusiast and professional busman
www.bustoshow.org
Blog: www.lookatthatbus.com
Instragram: @lookatthatbus
charles_m is offline   Reply With Quote
Old 07-29-2015, 01:12 PM   #10
Almost There
 
Join Date: Jul 2015
Location: Vermont
Posts: 91
Year: 1996
Coachwork: Turtle Top
Chassis: E-Super Duty
Engine: Ford 7.3 Powerstroke
Rated Cap: 13-passenger


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 Images
File Type: jpg IMG_0125.jpg (188.6 KB, 198 views)
File Type: jpg IMG_0127.jpg (124.7 KB, 194 views)
File Type: jpg IMG_0128.jpg (203.1 KB, 194 views)
File Type: jpg IMG_0129.jpg (220.7 KB, 196 views)
File Type: jpg IMG_0130.jpg (203.5 KB, 194 views)
sproutroot is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Virginia Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 08:05 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.