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rockies
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# Posted: 21 Sep 2019 06:32pm
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In looking at dc powered fridges I found a model made by Unique off grid appliances (model UGP-370L1 B) which can operate on either 12 or 24V. It has 13 cubic feet and uses 587 Wh/24 hrs (total watt hours stable running on 24v). It also says it the power consumption is 62w on 12v/24v.
What does this mean? Why the difference between these two values?
When I look at a regular ac fridge from Home Depot (model GPE12FGKWW) it says on the energy star website that it uses 307 kWh/yr.
Is it worth it buying a dc fridge for off grid?
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Atlincabin
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# Posted: 21 Sep 2019 07:38pm
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I would guess (and it's just a guess without knowing more from the manufacturer) that the fridge uses 62W when it is running, so gives you an idea of the draw if you have limited capacity. Fridges don't run constantly, so the 587Wh probably represents the total power consumption over the course of an "average" day. It seems reasonable to me, as I understand that most fridges actually run about 30-35% of the time. Multiplying that daily usage by 365 days/year yields an annual power usage of 214 kWh. So it would appear to use about 2/3 of what the other (AC) fridge uses. Assuming they are the same size in cubic feet, then the DC one is clearly more efficient. Whether that is because of the compressor etc. or it is just insulated better, I can't tell you.
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ICC
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# Posted: 21 Sep 2019 10:46pm - Edited by: ICC
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Quoting: rockies What does this mean? Why the difference between these two values
Atlincabin is correct. The 62 watts is an instantaneous measurement; 62 watts being used at any moment the compressor is running.
The 587 Wh is watt-hours, the total energy used over a 24 hour period. Multiply that x 365 to get the annual use. 587 x 365 = 214,255 watt-hours or 215 kWh.
I am a fan of the DC powered Danfoss compressor. I have one in my RV. But the published data of 587 Wh should be taken with a grain of salt, IMO. That seems low.
Because it is a DC appliance it never used to qualify for Energy Star testing and labeling. I do not know if that has changed. Probably not as I didn't notice any Energy Star claims in their brochure. So that raises the question to me if the test conditions Unique uses are the same as those used for the appliances [120 vac] that qualify under the E_Star program? Maybe they do. Who knows?
Which brings me to a pet peeves of mine. Both Samsung and LG make small refrigerators that use the energy efficient linear compressor technology. However, those are very difficult to buy in the US. I guess there is limited market as so much in the US is predicated on the bigger is better premise. We can buy their large ones, I have one.
They make some great fridges that are only sold in places like SE Asia and India. 8 to 10 cu ft. Top or bottom freezer. Some can be run with the fridge active and the freezer off. And vice versa. Some will let you select which section is the freezer. Truly innovative. Would make a great cabin fridge. But we will never see one here. No sense trying to import one as they will be 230 volts and 50 Hz. Plus a lack of parts if needed.
As for whether or not DC makes sense over AC. I used to think so. Maybe DC fridges do not make sense any more IF you are going to have any other AC devices that use largish amounts of power, like microwaves, toasters, high powered blender... I have all those. So what is one more AC appliance. And a linear compressor fridge does not need a huge inverter as they do not have the typical fridge start surge.
So, IMO, AC or DC??? Depends.... But I suggest NO to DC fridges.
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creeky
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# Posted: 22 Sep 2019 09:41am
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Ive come to the same conclusion. A cheap fridge with the money put towards the solar system has given me the best bang for the buck.
Keep the fridge under 350kwh/yr and you're golden with a 1kwh solar system.
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neckless
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# Posted: 22 Sep 2019 09:27pm - Edited by: neckless
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it is my under standing that the solar fridges are really a gas fridge with a 12v or 24v element intsead of a flame
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ICC
Member
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# Posted: 22 Sep 2019 09:38pm
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Quoting: neckless it is my under standing that the solar fridges are really a gas fridge with a 12v or 24v element intsead of a flame
Not the fridges sold by Unique and other brands that specify they use a Danfoss/decor compressor. Very efficient motor driven compressors.
Fridges sold for RV's that also use propane use AC and DC electric wire wound resistance heaters. Not good for solar as a rule. Some of the propane fridges like Servel also have an AC option that is a resistance heater. Servel sells that as an option to use with a generator if you run out of propane. Not meant for main use.
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Brettny
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# Posted: 23 Sep 2019 07:20am
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The energy star tags you see with a KW rating mean nothing. Dont even bother looking at them. Also any frost free fridge/freezer will have a heating element in it. They can take alot of power.
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Scott G
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# Posted: 23 Sep 2019 08:54am - Edited by: Scott G
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We bought a Marathon 15cu 'inverter' fridge. It's a normal big box stores fridge. Paid $699+ tax. Its been running for the past 2 weeks on a Bobolink Solar, "aka Creeky" system. Flawless so far. NRG Star at 325kw/yr. System is basically a 2200w PV, 10kw lithium battery (8kw usable), 3kw inverter.
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ICC
Member
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# Posted: 23 Sep 2019 03:20pm
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Quoting: Brettny The energy star tags you see with a KW rating mean nothing.
Why?
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rockies
Member
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# Posted: 23 Sep 2019 08:20pm
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Info on Energy Star vs Consumer Reports energy evaluations.
https://www.consumerreports.org/cro/news/2014/03/don-t-be-confused-by-the-new-energyg uide-label/index.htm
This article says that the testing procedures to calculate energy usage have recently become more stringent. I would think that if that is true then the appliance energy star label would be accurate.
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Brettny
Member
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# Posted: 24 Sep 2019 08:32am
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Energy star rstings are per year. You really need daily numbers for solar. Do your own calculations, a kill A watt meter is $20.
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ICC
Member
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# Posted: 24 Sep 2019 10:12am
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The testing procedure changed in 2011 to better reflect real world use. Similar to how the fuel mileage methodology changed in 2008 and 2017. To me the important thing about them all is that you can compare one brand to another and get relative efficiencies.
I don't see a problem with annual figures.
Annual figure divided by 365 = daily figure. 
Don't worry about leap years. 
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Brettny
Member
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# Posted: 24 Sep 2019 03:12pm
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Its true that you can use it to compair models. But dosnt really help with exterior conditions. A fridge in the 100* blazing sun will run alot more than one in someones basement.
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ICC
Member
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# Posted: 24 Sep 2019 04:10pm
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Of course. It would be unrealistic for anyone to expect anyone could accurately predict their real world use. EnergyStar was always meant to be a guide.
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kittysmitty
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# Posted: 24 Sep 2019 06:34pm
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The numbers do help you compare models. But, like fuel mileage if you are towing 10,000 lbs, the numbers change. Energy Star will compare models under the same conditions, but may not reflect your actual usage.
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rockies
Member
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# Posted: 24 Sep 2019 07:11pm
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By "exterior conditions" I assume you mean the temperature in the room. Of course, if the room is 100 degrees your fridge will take more energy to keep cool than if the room was 70 degrees.
The fridge itself, however, is tested with its fridge and freezer compartments set at a certain temperature and the room temperature set at about 70 degrees so that does allow every fridge to be evenly compared.
However, since it is true that the energy star fridge will use more energy to keep cool in a hotter room then so will the dc solar fridge. My concern was whether the added expense of buying the dc fridge was worth it compared to a much less expensive ac fridge (despite the higher amount of energy to operate the ac fridge). Apparently it's better to stick with ac.
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Brettny
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# Posted: 25 Sep 2019 11:45am
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It may also be cheaper to stick with AC. You can get a ton of line loss with low voltage DC and you cant just go down to tje store and buy a new fridge if needed.
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paulz
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# Posted: 16 Oct 2019 10:56am
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You have probably heard about the planned power outages out here on the left coast. So a co worker bought this dc cooler in prep, then decided he didn't need it and gave it to me yesterday, still in the box! The spec sheet says 2.3a at 12v, 55 watt. Does that compute?
Could have sure used it this summer, not so much now.
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Brettny
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# Posted: 16 Oct 2019 02:31pm
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Its prob more like 2.3a at 120v. Does it have a transformer on the plug to get it down to 12v?
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ICC
Member
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# Posted: 16 Oct 2019 03:20pm - Edited by: ICC
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The box end shows 23/24 volts. So, 2.3 A at 24 V = 55 watts. At 12 V that would be more like 4.6 A ???
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paulz
Member
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# Posted: 17 Oct 2019 09:31am
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Yes, upon closer reading they just flipped the amperage in the instructions. I would have noticed had I not been in such a hurry to brag about the new toy. It has a regular ac cord and a dc cigarette lighter plug cord but no transformer and they both go in the one socket. I wonder if can sense input and adjust?
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Brettny
Member
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# Posted: 17 Oct 2019 09:36am
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My parents have two of these type of coolers. The specs lie. Plug it in and put it on a killAwatt meter for 24hrs then tell us what it uses.
The fact that its specs are wrong right on the box tells alot.
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paulz
Member
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# Posted: 17 Oct 2019 09:55am
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Thanks Brett. Correction, just found one of those laptop type freestanding transformers for the ac cord in another box.
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Brettny
Member
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# Posted: 17 Oct 2019 01:13pm
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What do the specs on the transformer say?
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paulz
Member
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# Posted: 18 Oct 2019 09:47am
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Transformer says 110-240 in, 14.5 dc out 6.0 amp.
Probably won't get around to trying it for awhile.
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Silsen
Member
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# Posted: 9 Jun 2020 10:48pm - Edited by: Silsen
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I’m looking at that Marathon 15 cu ft inverter fridge. Now that you have had it for some time what is your overall impression?
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zorro
Member
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# Posted: 10 Jun 2020 01:45pm
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Just for info and in case of any interest
I got this for my camp and it works perfect - even has a small freezer compartment for making ice
https://www.danby.com/en-us/products/compact-refrigerators-en-us/dcr044a2bdd/
All linked to my solar system;
1020W panels
8 x batteries
1500W inverter
Generator back feed for batteries as required/when running well, etc
But it is great and perfect for what we need
No significant draw on the batteries and it is left permanently plugged in/switched on when we are at camp
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zorro
Member
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# Posted: 10 Jun 2020 01:50pm - Edited by: zorro
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And it fits perfectly into the kitchen, under the counter top
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Nate R
Member
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# Posted: 10 Jun 2020 04:01pm
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Zorro, great feedback! I was just looking recently at a 4.4CF fridge for similar uses.....
Any idea how much power it uses in a day? Probably not, eh, it's all mixed in with other AC loads at your place?
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zorro
Member
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# Posted: 10 Jun 2020 04:11pm - Edited by: zorro
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Actually I do!!
Before i put it into the cabin, I ran a kill-a-watt meter on it for a couple of days, just to be 100% sure my system would cope
Here are the results and honestly, it works perfectly and is ALSO..................wife friendly - which was critical 
So i ran the meter for exactly 48 hrs
Start up - 465W......for about 5 seconds
Then it runs around 55w constantly
In 48 hours, total use of 0.88kwh
So around 0.5kwh per day...............from my reckoning
I am not an expert, so hopefully that helps
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