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DIY: How to make your own 12V Fridge
Thanks for the details. I love it when people have measuring tools and use them and share their observations.

Dig the DIY experimental mindset too.

If you could gather some data on how much the fridge consumes over a time period would be a good figure to have. Such as mine( vitrifrigo c51is) runs usually no more than 20 minutes per hour, UNless of course i am opening the door a lot or just put a bunch of warm stuff inside. When full and when empty, the duty cycle is much different too.

I put one of these on the DC input to measure WH and AH consumed:

Evacuating heat from the condenser is where some of the biggest gains in efficiency are to be had. My Danfoss/secop has a radiator style condenser with an upgraded 120MM computer fan attached( Noctua NF-f12). Rather than just let this fan circulate air it itself has heated, I made mine pull cool filtered air from the floor below and the air pushed ( not pulled) through the condenser has no chance of being recycled through condenser. That and extra insulation and basically the only time I worry about my fridge, is when it needs a defrosting after a period of time with lots of humidity.

The more ice on the evaporator plate, the less efficient the fridge is, as the ice is insulating the cold plate, preventing it from extracting heat from the interior. My last defrosting was overduw and the duty cycle and interior temps dropped considerably once I rid the evap plate of all the Ice build up.

I also have a 0.03 amp 40mm 12v computer fan inside which greatly speed the cool down of items placed within and evens out internal temps nicely. My cheap american swill beer is at this moment, 33.5f.
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Yes we like experiments and back up data. I would suggest a condenser based soft start for your compressor and then just use one inverter. The mariners use such soft starts for their air conditioners. Using two inverters to power one device will prove to be complicated. If the inverter is only on while the compressor is running, does it make that much difference what the efficiency of the inverter?
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(06-15-2016, 09:28 PM)ahh_me2 Wrote: I plugged in my kill a watt meter onto my small 120 volt fridge today, and I will run it for 4 days or 96 hrs.
I will then put that same meter on to my Engel 12 volt compressor fridge for the same amount of time, as it is currently hooked up to 120 volts.
Then I will run the Engel off of 12 volts, and use one of my RC watt meters for the 96 hours and get the results based on 12 volt input.

I'll report back when done.

Ok, so I've gone over the 96 hour mark, I had a detour when both my vehicles developed brake problems.

My first fridge is a 4.4 cu.ft(124 qrts) Master Chef, 120 volt unit with a rating of 226 kwh/yr.
This should equate to roughly 226/365=0.62 kw per day.

My test period has been over 9 days with an ambient temp of 75 F, and an internal temp of 34 F.

My Kill A Watt meter shows the following:
2.7 kw used over 9 days
4.6 amps start current
0.6 running current
290 watts start power
46 watts running power
I wasn't able to determine the duty cycle as I was away most of the time

2.7kw/9 days=0.3 kw/day

If using an inverter we would use at a minimun the following, not counting losses in the inverter:
290 watts /12 volt= 24 amps starting power at 12 volts
46w/12v= 3.83 running amps at 12 v

Now I will run my Engel on 120 v for the same 9 days and report back
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Each spring in my area we get these "door to door" meat salesmen cruising up and down the streets in small  pickup's with an 8 or 9 cubic ft chest deep freezer in the back of the truck.   I looked at one once at a gas station
and inquired as to how he ran the freezer.  

The guy pointed to an inverter  and said that it was all it took and cost about $150 bucks.  The truck, freezer, and inverter was all they needed to be in business. 

Of course in their door to door sales the truck was always running and when they got home the freezer got plugged into a short extension cord from the house electric.

I can imagine a vehicle with a battery bank being able to sustain a small fridge at least as well.
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On boats, a chest type reefer was the norm with cold plates inside and 4" or more insulation. The compressor only had to be run for about an hour a day to keep things cold. Sometimes the compressor would be engine driven. The worst place to put the compressor or condenser is under the box, or even right next to it. Heat flows from warmer to cooler. Any kind of heat next to the storage box causes heat to enter the storage box.
With a side opening reefer the cold air inside is lost whenever the door opens, so the compressor has to pump back out all the heat that entered the reefer. With a chest type reefer the cold air stays inside as it is denser and sinks.
Google boat refrigeration. here is just one site.
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The following 1 user says Thank You to DannyB1954 for this post:
eDJ_ (07-09-2016)
any updates ViaVacavi or ahh_me2?

Ford E450 Box Truck RV Conversion
...but no pictures thanks to Photobucket...
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I'll have an update tomorrow, I've been so busy putting in my gas/water system I didn't realize I overshot the 9 day mark.
I'm at 17 days right now, so if I wait til tomorrow, it'll be 18 days which is a multiple of 9, makes it easier to use as a number.
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Ok, I have some more numbers, this time for 18 days, twice the time of the last test, but a multiple, so easy to compare.

The other thing that is different, is that while I am comparing the numbers from a 12v compressor fridge and a small dorm fridge, in this particular measurement, the Engel is running in freezer mode, and is running off of 120 v.

Using my Kill-a-watt meter, I have measured:
13.3 Kw over 18 days
0.90 amps start current
0.090 amps running current
65 watts start power
50 watts running power
4 watts at rest

Duty cycle, it seems to come on for 20-30 seconds every 5-8 minutes in freezer mode (-16 C).

So over nine days, we would use 13.3/2= 6.65 Kw in freezer mode versus the 2.7 kw for the 4.4cu/ft dorm fridge over the same time period. Both units sit beside each other in my shop.

The Engel is a MT-35 which is a 35 qt unit, the dorm fridge is rated 4.4 cu/ft or approx 125 qts,
which means the dorm unit is approx 3.5 times larger than Engel.

I need to run my Engel off of 12 v for the next test, it will be in freezer mode, and then I need to run it in fridge mode at 12 v again, in order to find out it's real performance.

I also have a small 1.1 cu/fridge in the cube van while I am living in/building it.

It is rated @ 207 Kw/yr and I should run the same test on it, as it is 4 times smaller than the 4.4cu/ft one but most certainly doesn't consume 1/4 of the power.

I'll report back in the future!
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The following 1 user says Thank You to ahh_me2 for this post:
BradKW (07-12-2016)
I don't have the data to back it up but having used a pair of Whynter 65 qt units, one as a fridge (at 40F) and the other as a freezer (0F), I can safely report that there is a huge difference in power usage between the 2 of them.

So much so that I can run just the one unit as a fridge for up to 4 days without needing to recharge my battery system (450 ah). I cannot run the pair of them in the above configuration for more than a day without recharging the batteries.

Since I have shore power available all this summer, I have moved the freezer to my cargo trailer which stays put while I go places. In particular, I ran in  to a logistics problem when planning a 3 day canoe trip. I couldn't leave the van at the access point for more than overnight because of the freezer. The first canoe trip I took, I ended up putting the entire contents in a friends deep freeze so I could go canoeing!!

I guess I should go borrow the Kill-a-watt meter from the local library and actually do some testing.
Worry is a misuse of imagination!
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Full-timer again as of November 24, 2015 - 14 glorious years on the road before that!

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on my Engel when I us one as a freezer. I flash freeze everything in it by turning it down all the way. this will freeze everything rock solid in 12-24 hours depending on ambient temps. then I turn it up to about 3(the dial goes from 0-6, 6 being the coldest) this keeps everything like a rock even in 100 degree weather. if I am using it as a refer and turn it up to 2.5 it will turn beer to slush.

I don't have numbers to back this up but I can run my 2 Engels off of 160 watts of solar and 2 12v marine batteries no problem even with several days of cloud cover. before I got the Engels I tried using a dorm fridge after the second night my batteries would be below 50%, even one cloudy day and it wouldn't make it to the second day. maybe the dorm fridge I had was a lemon. but it worked fine of off 120v. this turned me of to dorm fridges. for me it was a waste of good money. highdesertranger
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The following 1 user says Thank You to highdesertranger for this post:
southern.nomad (01-22-2017)

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