DIY: How to make your own 12V Fridge

[ahh_me2]

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

 

[eDJ_]

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.

 

[DannyB1954]

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. http://www.sailmagazine.com/cruising/cruising-tips/choosing-the-perfect-refrigeration-for-your-boat/

 

[BradKW]

any updates ViaVacavi or ahh_me2?

 

[ahh_me2]

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.

 

[ahh_me2]

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!

 

[Almost There]

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.

 

[highdesertranger]

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

 

[ahh_me2]

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.


I guess I should go borrow the Kill-a-watt meter from the local library and actually do some testing.

There should be a large difference IMO, between fridge and freezer mode, in terms of power consumption.

One of the reasons I am doing this test is because very soon I have to make a decision, buy another Engel as a fridge
or use a dorm fridge. For me anyway, having a decent fridge and freezer is simply a must!

So by playing with a number of permutations of 120v and 12 v systems, I hope to find the optimal point for me.

Unfortunately waiting 9 days for each test, or 18 even lol, makes it a slow process.

Almost There, remember a kill-a watt is only for 120v, you need an RC type for low voltage, ie 12v.

What I am ultimately trying to figure out in part, is which mode is more efficient on a so called 12 v compressor fridge.
If they are a true 12 v system, and the 120 v that is fed into them is regulated down to final 12v for the compressor, then I would expect they should consume more power at 120v due to inherent losses in the down regulation. I still need to prove that out.

 

[ahh_me2]

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.

Ok, no more tests! I don't want to try that! hahaha

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

I hear ya, and I aim to find out because the theory is that you are correct, the practice...well...I just can't confirm yet either way.
I figure another month and I will have final numbers, to ...well....we'll see I guess...

 

[Almost There]

Almost There, remember a kill-a watt is only for 120v, you need an RC type for low voltage, ie 12v.

Well, at least I'll be able to test power consumption on 120 since the units are dual power.

That will at least give us some idea of the difference between using them as a fridge and as a freezer.

Maybe next winter I can borrow an RV type while in AZ and test it on 12V

 

[BradKW]

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...

 

[jimindenver]

A mini fridge built for price point will be inefficient. One built to be efficient will cost ya. That's why the smallest cube fridges can use as much power as a medium sized 2 door.

Somewhere along the line I have heard that the refrigerator is 20% of the energy bill. You pegged it.

 

[jimindenver]

I was given a RCA 3 ft mini fridge with a even minier freezer rated at .8a @ 120v. So roughly 8 amp at 12v plus losses. I use a 235w panel to keep the system up, it gets 5 solid hours at 14-15a and some shoulder output mid winter.

At a 50% duty cycle the fridge uses 96a plus losses, the panel puts out 75a plus shoulder output. It was almost enough but it wouldn't have been close were the panel flat. It would chip away at a smaller bank and a cloudy day would really take a bite.

We gave the fridge to the mother in law. The one I want is a two door, has a bigger freezer and uses less power. Many are rated at 1.5a @120v, even cubes. At that power level or slightly higher there are 9 and 10 ft models.

 

[BradKW]

I've been working through a "second round" of 'fridge shopping now that I know a bit more about my power budget and what the numbers actually mean. 

And honestly, I have to say that in some ways, ignorance was bliss. I assumed that if one paid $1300 for the 12v/24v flavor of a mini-fridge that the energy savings versus the $130 one at Home Depot would be amazing. Turns out that's not really true...the "amazing" part definitely not. I have actually found expensive RV fridges that use about the same as my old Kenmore...if it weren't for inverter inefficiency, the $130 would tie the $1300 one.

Here's a decent comparison I think: Vitrifrigo Sea Steel C115iXAC for $1100 uses 45 watts. My old Kenmore uses 71 watts. A Vitrifrigo Sea Classic DP2600iAC Refrigerator / Freezer for $1600 uses 65 watts.

And here is a $1100 Dometic CRX-1110 3.7 cu/ft that uses 72 watts... what the heck??

I feel like I must still be missing something, because it sure appears that huge price tags don't equate to much energy savings...?

 

[ccbreder]

how much refrigerated space do we need. grocery stores Walmarts in every town. deep into western wilderness could be handled as it has been for centuries.

 

[BradKW]

how much refrigerated space do we need. grocery stores Walmarts in every town. deep into western wilderness could be handled as it has been for centuries.

Well, aside from nearest Walmart being 100+ miles away, what I "need" is a way to keep 1.5 cases of assorted beverages cold, as well as leftovers from my once-a-week cooking that I eat through the week. Deep in the wilderness sounds wonderful...unfortunately I have to work a lot which leaves me without the time or willingness to focus on small things, such as keeping my daily supply 8-pack of water/gatorade/propel cold.

 

[ccbreder]

Don't worry, my friend. WAWA is coming to Florida!

 

[jimindenver]

A case and a half plus a weeks worth of food is a fair amount of space. Does it fit in what you have now? Our 5 ft fridge limits us on longer trips so we have a one can out, one can in system for pop and beer. When all the cans are still warm, we are drinking too much. lol

I like to pre-cook with the solar ovens when I can. One good day and a weeks worth of meals is easy.

 

[SternWake]

I've been working through a "second round" of 'fridge shopping now that I know a bit more about my power budget and what the numbers actually mean. 

And honestly, I have to say that in some ways, ignorance was bliss. I assumed that if one paid $1300 for the 12v/24v flavor of a mini-fridge that the energy savings versus the $130 one at Home Depot would be amazing. Turns out that's not really true...the "amazing" part definitely not. I have actually found expensive RV fridges that use about the same as my old Kenmore...if it weren't for inverter inefficiency, the $130 would tie the $1300 one.

Here's a decent comparison I think: Vitrifrigo Sea Steel C115iXAC for $1100 uses 45 watts. My old Kenmore uses 71 watts. A Vitrifrigo Sea Classic DP2600iAC Refrigerator / Freezer for $1600 uses 65 watts.

And here is a $1100 Dometic CRX-1110 3.7 cu/ft that uses 72 watts... what the heck??

I feel like I must still be missing something, because it sure appears that huge price tags don't equate to much energy savings...?

In todays world of ignore logic and quality and use Marketing for maximum profit, any published specs really mean little.

The proof is in the KWH meter in actual usage, and there is no standard to which manufacturers are held, and I doubt any enforcement of tany rules or condemnation over their outright lies.  My inner cynic says they just write something somewhat believable and focus instead on marketing( influencing public decisions via dishonesty and trickery).

My initial fridge strategy was get a 12v compressor fridge and enough solar for it.  It was an AC/DC norcold DE-0040, and when it arrived I ran it in a garage, in florida, in summer, and every dang time I walked by it, the compressor was running.  i freaked out a bit assuming the 130 watts of solar would not be enough.

I had not yet build a cabinet for the fridge, so I added a lot more insulation to the fridge body, I designed the cooling unit ventilation so that it could extract the heat generated as best as possible.  I added a small internal fan.

When Installed, and I ran the fridge overnight and for a few days I saw 130 watts was about 2x as much solar as I needed.

That fridge lasted 5 years.  I replaced it with a Vitrifrigo c51is, to which I also added extra insulation, and whose cooling unit design allowed me to further improve cooling unit air circulation.  The VF is about 10 to 15% more efficient than the Norcold was, and makes 1/3 the noise.  I now have 198 watts of solar, and worrying about fridge energy consumption or spoiled food, or finding block ice are simply distant nightmares long in my past.

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.

I am not familiar with 120Vac fridge compressors their efficacy or efficiency, all I know is that I hate Inverters, and marketers, and My VF c51is kicks burro and was well worth the ~600$ I spent on it in october 2012.  Pre 2007 I used to spend nearly that amount  per year in block ice, not counting the gas or inconvenience required to got get more when required, nor all the spoiled food I threw away when I did not replenish the ice soon enough.

Not having to deal with block Ice is priceless.

Keep in mind when the standard 120 vac dorm fridge is run on an inverter, the inverter is only 80% efficient, but when the compressor is not running, the inverter is also consuming its standby load, doing nothing while waiting for the compressor to kick back on.

My MWS inverter's standby draw, turned on, powering nothing, is 0.68 amps.

Turned on powering nothing, this 800 watt MSW inverter will consume MORE than my VF 12vDC fridge will over the same time span, 80% of the time as i use it.

My beer is 32.5f as i type, in 82F ambients.
 battery 3Ah from full, solar making 6.5 amps total, holding 14.1v in overcast conditions.

I have not turned on either my PSW or MSW inverter in weeks.