DIY: How to make your own 12V Fridge

[BradKW]

Yeah, I (kinda) know...and odds are 10:1 that I'll end up with a Vitrifrigo. I was leaning toward it anyway and remember your positive experiences with it. Which reminds me, I think you know who a Vitrifrigo rep is from another forum? I lost track of his info and need to find it again, main distributer is in Ft Lauderdale and I imagine I can save shipping when I go to pick up batteries. Think he had Volkswagon in his screen name...?

I really like the looks of this:  

...and if I can figure out how to work the oddball 53" height into the design, I'll probably go with it. I'm terrible about starting with a $800 unit, ooh wait, that $1100 is much nicer...well heck, might as well get what I Really want for $1500    :/

 

[BradKW]

I really like the Danfoss/secop compressor fridges, as one can influence compressor rpm( and amp draw when compressor is actually running) by introducing resistance to the thermostat circuit, One can add computer fans, upto 0.5amps total, that are switched on and off with compressor and help remove heat from condenser and compressor and condenser controller.  One can also hook up a light to the controller and pull diagnostic codes rather than simply scratching their heads in bafflement with other compressors when it no workkee no more.

From a manual: 
"Thermostat (Fig. 10) The thermostat (7) is connected between the terminals C and T. Without any resistor in the control circuit, the compressor with electronic unit 101N0210 or 101N0220 will run with a fixed speed of 2,000 rpm when the thermostat is switched on. With the thermostat directly connected to terminal C the electronic unit 101N0300 will adjust its speed to the actual cooling demand. Other fixed compressor speeds in the range between 2,000 and 3,500 rpm can be obtained when a resistor (8) is installed to adjust the current (mA) of the control circuit. Resistor values for various motor speeds appear from Fig. 14. Fan (optional, Fig. 10)

 A fan (5) can be connected between the terminals + and F. Connect the plus to + and the minus to F. Since the output voltage between the terminals + and F is always regulated to 12V, a 12V fan must be used for both 12V and 24V power supply systems. The fan output can supply a continous current of 0.5Aavg. A higher current draw is allowed for 2 seconds during start. "

Question: without user input, compressor runs at 2000 rpm...unless the thermostat is connected, then it will vary based on demand? Why wouldn't thermostat be connected?

Why would you want to use the other option of manually making it run faster (less efficient) with a resistor?

 

[SternWake]

Question: without user input, compressor runs at 2000 rpm...unless the thermostat is connected, then it will vary based on demand? Why wouldn't thermostat be connected?

Why would you want to use the other option of manually making it run faster (less efficient) with a resistor?

Thermostat wire is still connected, just with no resistor inline.  

This is the 270 OHM resistor provided to run mine at 2500 rpm.

I removed it as I do not require the quicker cool downs and shorter duty cycles of a faster compressor speed.

The danfoss bd35f can handle a pretty large fridge at higher rpms. It is just cruising along powering my 1.8 cubic foot fridge.  I do sometimes think about putting a potentiometer inline on this T stat circuit so those times when i load it with warm beer, I can cool it down faster.  How much faster?  IDK.  I don't think I'd want to push it to 3500 rpm as the evaporator plate likely does not have enough surface area to make the extra rpm in the 2800 rpm+ useful.

They say the slowest compressor speed which allows duty cycles no bigger than 50%, is most efficient.  My duty cycles rarely exceed 33%.



http://www.westyventures.com/parts.html#cart_restore

The VF distributor is located in FT lauderdale or thereabouts.  At least that is where mine shipped from, fedex.

You might see if some marina in that area can get you the bro price if you pick it up since, you are not too far away. 

Sorry for going off topic.  VFs/danfoss are a different thread.

 

[jimindenver]

Plugged my kil-o-watt into my Kenmore 4.4 fridge (has a little freezer compartment too) and averaged 0.9 kW per day on 110v. Figure inverter loss, and that equates roughly to 20% of my daily budget of 5220 Wh (50% of total 10440 Wh).

Certainly doable, but fairly inefficient. I think you'd basically have to have 200W solar and 160 Ah battery bank to make it work with a little left over...

I wanted to speak to your daily energy budget. It truly isn't half of the power in your bank, it's how much power can you produce with your system in a day. Like me you have a better than 1-1 ratio of solar watts to battery Ah and I'd be hard pressed to have to replace the over 300 Ah the batteries offer daily. It's a numbers game when you see it. The system puts out x amount of power and the bank needs x amount to bring it up. 1-1 is nice but you need 2-1 to start pushing a big bank around.

A example is I did a capacity test on the old 8-D. The next day I put a 220w panel tracking the winter sun on it and after 5 hours it was up to 13.0v under charge. No where near what it needed to be full. The panel was putting out 12.75a for five hours and the battery was down 120 Ah's, it need another day at least. At 2-1 my 490w system putting out 34a could have handled the winter day.

Location, time of year and conditions all affect you energy budget. Winter sun is up less and lower in the sky meaning reduced output, a double whammy. We had smoke from forest fires last year, we were above a lot of it but that haze cost us 5a in every condition. Overcast conditions cost us 50% and we see them near every afternoon. Shoulder hours are a slow crawl to peak and not nearly as much output as you think. The sun is so low that my 235w portable can out pace the larger flat system from sun up to 9 am.

So the only way you can say that your energy budget is half of your storage capacity is if you can guaranty that you can put it back in the next day. That means a big converter and generator or a alternator that can support putting out high amperage for hours. My trailer has a 55a converter, care to listen to a generator all day? My generator would support a 120a converter but even that would need to run for 3 hours. Both of our banks have big numbers and we have to think in those terms.

 

[Trebor English]

Here are a couple of videos where he insulated the mini fridge and reduced the power consumption by 40%.  The R13 fiberglass is ugly but you could get the same result with R13 of foam.

Convert a Standard Minifridge into a High Efficiency Refrigerator - Part 1/2


Convert a Standard Minifridge into a High Efficiency Refrigerator - Part 2/2

Trebor

 

[ahh_me2]

Update on some more tests:

I ran the Engel 12 v compressor fridge in freezer mode at around 5 F with an ambient temp of around 75-80 F, the setting on the Engel was just a bit past 4.
The average consumption was around 45 A/H's per day.
But this was with the freezer set for holding frozen goods for long term.
If one does what HDR is suggesting, one could "flash freeze" then dial it back some and hold frozen foods for a couple weeks without any issue.
This would result in a lowered consumption of power.

Next was to defrost the freezer and restart it in fridge mode, let it come down to temp and stabilize around 34 F. The setting on the Engel was a bit over one.
This seemed to average around 17 A/H's per day.

Comparing to my 120 v 4.4 cu/ft fridge, which consumed around 300 watts per day, which translates to roughly 25 A/H per day running off an inverter however we haven't figured in inverter losses.
At 80% inverter efficiency it would cost us another 5 A/H's and would bring us to 30 A/H total.

The Engel is rated for up to 30 degree tilt without issues, and the home fridges are not supposed to be moved around and especially not bounced around in the back of a vehicle without letting it sit for 1-2
hours before engaging the compressor, and they are supposed to be set in a level position for proper operation.

The 4.4 cu/ft fridge translates to around 124 quarts and the Engel is rated at 35 quarts.

Now one more thing, recently a few people had posted about Truckfridge brand and so I looked into them.
What I found on their FAQ page and in the specs was a 4.4 cu/ft front load 12v compressor fridge requires an average of 40 amps per day, this is way more than my Engel and quite a bit more than my 4.4 cu/ft 120v model.

So I  am still perplexed as published ratings and actual readings seem in dis-agreement somewhere.

SO I decided to see if my 400 watt MSW inverter would run my 4.4 cu/ft fridge, it looks like it does, but it's in awkward area to monitor.
I then realized I can run my small 1.1 cu/ft 120v fridge that is in my van off the inverter and watch my watt meter and get a better idea of power usage.

Unfortunately I haven't been able to come up with definitive numbers pointing me which way to go on these dang fridges, so I have to keep testing.

Hopefully back in a few days with more numbers...

 

[highdesertranger]

were the refers empty during the tests? or full? just curious. good point about running off level maybe that's why I had bad results when I tried the dorm refers. off road driving is anything but smooth and level. although I did try to level it once I set up camp might have been to late by then. highdesertranger

 

[ahh_me2]

HDR, they were stocked with standard items, frozen in the case freezer tests, and the normal items for the fridge mode tests.
I've been traveling around with the 1.1 cu/ft 120v unit for the past year, and it has stood up so far, and while I am parked at the office the dorm fridge sits at a fair angle
because we have quite the slope on the parking lot.

My gut says 12 v compressor should be better, but early indications point to a different outcome.
I just wish it was a much more drastic difference between the 2 types.

But again, I'll know more in a few days with hard data to backup whatever ends up being the outcome.

 

[akrvbob]

I have a TF51 Truckfridge and its drawing less than 20 ah a day and it's been about 90 for a week

 

[ahh_me2]

Thanks for the input ! That is comparable to my Engel MT-35 @ around 17 ah/day.

I don't know why Truckfridge specs say they draw 40 amps (480 w) average per day

 

[rvpopeye]

This is a very interesting and useful thread.I'm following along for the final results.
My class C came with a dorm fridge from the PO and I was looking at getting another with a separate freezer door. A big problem with the one door models..
After seeing so many threads about them lately , I am thinking about buying an Engle-Whynter-TruckFridge 12v. Seems like that type could use a shoot out thread too.
(While browsing Amazon yesterday I spotted a dorm fridge that looked exactly like a Marshall Amp ! Now there's a good reason to buy a fridge LOL)NOT !

 

[akrvbob]

Thanks for the input ! That is comparable to my Engel MT-35  @ around 17 ah/day.

I don't know why Truckfridge specs say they draw 40 amps (480 w) average per day

I guess I should have added that I put an inch of pink styrofoam on the sides and bottom of mine and keep multiple blankets and a pillow on top. 

Because I control the thermostat, I know exactly how much it runs every day and it's never been more 5 hours at about 3.5 amps.
Bob

 

[ViaVacavi]

I know it's been a while, I've had a very busy summer. I have a few days off coming up where I'm hoping to share my fridge conversion. The final result came out really nice. The end result was a 3.1 cu Ft refrigerator with freezer (around 100 quart capacity total) that uses in the low 30's amphours per day. The compressor averages about 6 hours per day of runtime

A model without a freezer section would of course else even less, and I haven't moved on to insulation improvements yet. So far I'm finding it quite comparable in performance to similar sized 12v fridges

 

[ViaVacavi]

A quick teaser while I put together a good DIY:

The conversion is very simple and can be completed in 20 minutes.  It uses two standard automotive Bosch style relays so that parts availability would never be a problem.  I also used a 4-terminal strip in my conversions, and added a 12v computer case fan.  The total cost, brand new was right around $150 ($129 for the fridge, a couple of relays for about $10, a 4-terminal strip for $5 and another $6 for a case fan).  The only cost I didn't associate with the conversion is the inverter, which was already being installed in the van for general use. The inverter was modified by replacing the switch with a 2-position terminal strip (about $2). The inverter can be connected to the modified fridge control as well as a normal switch in parallel. This allows for the inverter to be turned on if you want it for general us by using a switch, or by the fridge when it needs the compressor to run. This way, the inverter is ONLY on when either A) you have purposely turned it on with the switch, B) the fridge commands it to turn on, or C) When both the manual switch AND the fridge are asserting a signal to turn it on. In my tests, the inverter is losing right around 3-4 amphours per day running 6 hours on average since it switches off automatically. If it didn't have this feature and the inverter was on 24/7, the parasitic losses would add up to around 15-16 amphours per day.

The terminal strip, two relays and fan all mount neatly to the back.  Another added plus is that I also made my own auto transfer switch (tutorial coming soon on that.  Costs less than $10) so when I'm on shore power, the compressor will use that instead of inverter power, making this essentially a 2-way fridge.

[img=640x480]http://i827.photobucket.com/albums/...avi/IMG_20160812_115732_zpsdolalwj2.jpg[/img]

 

[jimindenver]

Some inverters like the one I use have a load sensing feature. Sans that feature that would be a good way to go. Thank you

 

[bcbullet]

I am seeing some big amp hours numbers here. My Grape Solar that I bought on a lark because of its huge size is only running about 13 a/h per day. I was really not expecting much at all from the fridge as I only paid $400.00 CDN for it from Amazon Canada, but it is literally working phenomenally! Of course the second I bought it the price jumped up to $700 the next day and now it is no longer carried. Link here from US amazon:
https://www.amazon.com/Grape-Solar-...8&qid=1471561954&sr=8-32&keywords=grape+solar
I believe Home Depot carries them as well in the States, but I have to say I have zero buyers remorse (for a change).

 

[ViaVacavi]

That's great if you're getting those kind of numbers!
But something isn't adding up. By the manufacturers own specs the unit should use in the low 20s amphours per day, and that 's normally under ideal conditions (70-72 degrees surrounding temperatures, which isn't realistic in a van in most climates) . Have you done actual measurements, or have you done any modifications? You're reporting nearly half of the energy usage stated by the manufacturer, and way more than half the usage of any other brands comparable sized unit. Nearly every comparable sized refrigerator that I've seen, whether AC or DC can barely hit numbers that double what you're seeing. I'm just wondering if there could be a measurement error involved?

 

[Spaceman Spiff]

Thanks, ViaVacavi!  I hadn't thought of using the compressor controller to turn on the inverter.  Excellent solution.  I anxiously wait your tutorial.

Some inverters like the one I use have a load sensing feature. Sans that feature that would be a good way to go. Thank you

I'm missing something.  If the inverter is off (no current flowing to the compressor) there can not be a load to sense.  What am I missing?
I'm a mechanical engineer, so I have a rudimentary understanding of electronics (and a great sense of amusement when EE's let the magic smoke out).

 -- Spiff

 

[jimindenver]

The Trip-lite PV1250fc can be set to turn off until a load presents itself and then it will turn on. It wouldn't turn on until the fridge tried to start its compressor.

 

[bcbullet]

That's great if you're getting those kind of numbers!
But something isn't adding up.  By the manufacturers own specs the unit should use in the low 20s amphours per day, and that 's normally under ideal conditions (70-72 degrees surrounding temperatures, which isn't realistic in a van in most climates) .  Have you done actual measurements, or have you done any modifications?   You're reporting nearly half of the energy usage stated by the manufacturer, and way more than half the usage of any other brands comparable sized unit.  Nearly every comparable sized refrigerator that I've seen, whether AC or DC can barely hit numbers that double what you're seeing.  I'm just wondering if there could be a measurement error involved?

I think we should be close...this is all based off a Bogart Trimetric and a hydrometer, so I have no reason to doubt it. The insulation in this thing is about 4" thick on the sides and bottom, all consumption done with an ambient average of about 80F. It easily outperforms the Dometic CF35 it replaced and it is over twice the size and twice the insulation. Like I said, I am blown away by it; literally runs less than 20% of the time and consumes about 3.1 amps running.