DIY: How to make your own 12V Fridge

[bonvanroulez]

I should also mention,to keep this on-topic; as I mentioned earlier I got a 12 volt version of the same temperature controller, and last winter purchased a 1,000 watt inverter with the plan of doing as the OP did and switching the inverter on and off with the fridge cycles. I was unhappy with the inverter I bought so I returned it, scrapping the project for the time being.

I could gain some advantage by doing the switched inverter, but as it is, with 200 watts of solar and 2 deep cycle batteries, all my power needs are easily met, even in the shortest days of winter. So, if I finally do the inverter switching mod, it would be as a fun project, not out of necessity.

 

[bonvanroulez]

Total AH per day @ 12V would be ideal for comparison, using a shunt-based meter.

The amp/hour listed above at 1.07, times 24 hours = 25.68.

Of course, using a shunt-based meter at battery voltage would be ideal. Can you suggest a device to record and track that data over time?
Will you buy it for me? 

 

[Trebor English]

I got a toy RC battery meter from Amazon.  The inverter current is pulses and that confuse the meter.  That meter now spends most of its time between the solar panel and the pwm controller where the pulses are slower.  What I use with the inverter is a Fluke meter that has an average function and an old time kitchen clock that contains a motor.  During off cycles the hands don't forget their position so on cycle times get accumulated.

 

[John61CT]

Cheap eBay AH meter with shunt $22.

Yes Victron 702-BMV would be much better

 

[AquaticsLive]

bonvanroulez That is pretty cool very similar project!

I haven't had mine setup too long but I will report back with some long term info. I do have a bunch of shunt meters setup in my truck as well split up by use. Electronics used to be my job and now is my hobby.

Has anyone tried putting a piece of insulation inside for the bottom half? Wonder if storing less needed items in the bottom and making a little piece of foam facing the door to block it off would reduce the need for it to cycle when opening the door.

 

[John61CT]

Likely marginal effect.

I'd just start with chest style in the first place.

Likely a freezer with a lot of insulation, but run as a fridge.

 

[bonvanroulez]

Has anyone tried putting a piece of insulation inside for the bottom half?  Wonder if storing less needed items in the bottom and making a little piece of foam facing the door to block it off would reduce the need for it to cycle when opening the door.

I did something like that.
I made a thin plywood cutout to snugly cover the lower part of the fridge opening, sorta hinged from a rack with a couple zip ties so I could lift it out of the way. I found the results weren't worth the trouble of having to lift it to get at items. It made very little difference in compressor cycles. It lasted about a week before I removed it.

 

[KMAG YOYO]

I read this thread but without the photos (thanks Photobucket!) it's hard to tell what's going on.. correct me ViaVacavi if I'm wrong but the only major alteration that is adding efficiency is that the inverter does not idle?

I like to have my inverter ready on demand so it does idle. IMO not a major power drain. 

My approach so far has been to improve the efficiency of the refrigerator itself. I don't have numbers but it does seem to eat a lot of power, my 230 Ah bank is down to 12.2V in one day without sun on the panels. 

Since the condenser coils in this fridge run under the surface of the appliance case, adding insulation to the outside would only make it less efficient. Instead, I added these square aluminum tubes as a heat sink. At the back of the cabinet is a 68 cfm computer fan that blows air onto the compressor unit and exhausts through the heat sinks. It uses a constant .15A (not relay controlled by thermostat). I would say this really only improved efficiency by a small margin, if at all. Need a kill-a-watt meter to be sure. 

 

[KMAG YOYO]

It's interesting that you can buy a 12v Danfoss compressor and retrofit it onto a dorm fridge, but the cost of the kit (from West Marine and others) is $800+. Then you have to get it charged. And, no guarantee that it will be any more efficient than a $700 Engel.

A friend of mine who is a shipwright built a custom fridge for his yacht using one of these kits. He started with a plywood cabinet which he filled with 3" of 2-part expanding foam, then added a fiberglass tub for the fridge interior. He said getting the tub to set straight and not float in the foam was a stressful experience. After hooking up the kit, he had it charged by a refrigeration technician and had a super efficient refrigerator.

 

[AquaticsLive]

I did something like that.
I made a thin plywood cutout to snugly cover the lower part of the fridge opening, sorta hinged from a rack with a couple zip ties so I could lift it out of the way. I found the results weren't worth the trouble of having to lift it to get at items. It made very little difference in compressor cycles. It lasted about a week before I removed it.

Good to know I won't waste my time on that then.

 

[John61CT]

> I like to have my inverter ready on demand so it does idle. IMO not a major power drain. 

Should not assume unless you have lots of spare capacity.

Easy to get a precise measurement.

 

[John61CT]

> a friend of mine who is a shipwright built a custom fridge for his yacht using one of these kits.

For OTS kits and DIY you're on your own:

Adler/Barbour ("AB") part of Dometic/Waeco now, "Cold Machine" product line

Isotherm is also good

SeaFrost https://www.seafrost.com, owner is Cleave

----
But for anyone considering spending the big bucks, totally worth it IMO if you want a **super-efficient** but nice & large (say 200L) combined fridge/freezer in a custom shape unique to your vehicle, e.g. replacing the front passenger seat, guts extended into the leg space, maybe batt bank underneath.

Continue to perform well - keeping ice cream rock hard, steaks safe for six months - even in 120° F conditions, as per US military specs for desert applications.

The best vendors in the world to deal with are:

(Eutectic holding plate systems)

Technautics, "Cool Blue" brand, 5yr warranty! contact Rich Boren, aka SV THIRD DAY on the marine forums, 619-609-3432, [email protected]

OzeFridge well recommended but in Australia


(Standard evaporator system)

ColdEh Marine Refrigeration http://www.coldeh.com in Canada, John Tully is the owner

Why all three of these vendors are so much more efficient and effective:

Massive insulation, 4" is just a starting point

TXV Thermally Adjusting Expansion Valve

Larger condensing unit, oversized drier/receiver to store the refrigerant, best with a sight glass installed.

As opposed to most makers, who save costs by using a FCO (Fixed Critical Orifice) capillary tube or CPV, (constant pressure valve) and thin rolled aluminum evaporator plates, with no hold over capacity.


The holding plate system, rather than evaporators, puts a large below-freezing thermal mass (eutectic solution) inside the insulated box. This reduces compressor cycling frequency dramatically, maybe 2-4 times per 24 hours (or even once!) rather than several times per hour. Longer on time per cycle obviously.

First, lots less wear and tear and inefficient start-up for each cycle.

More importantly, if you are periodically running a gennie, or have a lot of excess solar capacity after your battery bank is past 80% SoC and amps accepted is dropping, that's when you "recharge your plates" from the "free" excess energy.

If you don't have such periods of excess energy production, ColdEh has all the other efficiency improvements, but uses better-quality evaporator plates.

This eliminates the higher cost and extra weight / space used by eutectic holding plates in the other two vendor's systems.

 

[KMAG YOYO]

So, if I put something inside the freezer box (which is the evaporator plate) like a block of ice, or perhaps better, a solid chunk of metal or other material with large thermal mass, this would reduce cycling and therefore improve efficiency? I could add the mass before we drive and "charge" it while the alternator is running. Seems like a very easy way to stretch our battery capacity.

 

[highdesertranger]

in a refrigerator the more mass inside the better. usually the mass is the food you have it loaded with, liquids work the best. highdesertranger

 

[John61CT]

Yes, but the holding plates have the refrigerating gas passing though the inside of the (well below 0°) solution, re-freezing the whole big blocks every day, in some cases running only once a day, otherwise every 6-12 hours if you leave it on automatic.

Biggest advantage is as I said, if you control the on cycle timing, to coincide with excess energy production.

What frater calls an "opportunity load" I think, or "load dump" in wind generator terms.

Really the same thing in a way as adding an extra right-sized LFP bank dedicated to the fridge/freezer.

Without that advantage, most experts say holding plate systems are not inherently more efficient than evaporators.

Just that evaporator systems don't usually get the other expensive energy-saving features I outlined above - ColdEh's do however.

But OzeFridge vehemently insists that holding plates are inherently more efficient, and has run tests keeping everything else constant. He only sells holding plate systems.

Note that the biggest factor by far is extreme (by most standards) insulation, and not opening the unit more than necessary.

I really like the idea of a freezer compartment and "spillover" for the fridge, all off one compressor, and a large total capacity for the same AH per day as one much smaller portable unit.

 

[AquaticsLive]

Just a recap of my system and did a few tests to get a day of use.

Whynter CUF-210SS Freezer, 2.1 Cubic Feet
Mighty Max 1000w Pure Sine Wave Inverter.
12V DC Digital Thermostat relay.
bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter

Thermostat relay has with 3 degree Celsius between off to on. On the my Acurite thermometer its ranges from 38 F to 32 F.

I use the thermostat to turn on and off the inverter via wires jumpered off the inverter power switch. Its cool out I am in Iowa; but I keep the area above 70 all the time for my pets. The weather though effects it since lower humidity and warm temps to fight. It has changed the cycling time from about 28 minutes to 40 minutes and now it runs a little longer; it was about 3 minutes run time before now it runs about 5 minutes each time it cycles. This could be that I have more in the fridge now so I need to share that detail as well. So many variables to keep in mind.

24 Hour Test
233 Wh

 

[John61CT]

What are you using to measure consumption, is that total DC including the inverter?

 

[AquaticsLive]

That is total DC on the power line going to the Inverter. I have a shunt meter setup just for that line separate from the rest of my circuits.

I am using one of the "bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter" Got a three of them to keep and eye on separate circuits. I had originally bought them for multi-output power supplies I was building for friends; so leftovers to use up. I have way too much junk lol.

 

[bonvanroulez]

Just a recap of my system and did a few tests to get a day of use.
  
24 Hour Test
233 Wh

Thanks for posting this. Your results are consistent with what I posted earlier for the same converted freezer unit.

 

[highdesertranger]

so AW are you saying it runs on .8ah's? highdesertranger