# Refrigerator Considerations - AC or DC wiring

Registered Users Posts: 21
I am getting quite an education here on this forum. Bill (BB) responded to a query of mine on another thread, informing me that absorption refrigerators are extremely inefficient when run on electricity. The Dometic model in my RV (my RV is actually a Skoolie - school bus conversion) is an absorption type refrigerator. Looking into this subject further last night I found a lot of useful information, much of it on this forum. One suggestion was to use a chest type freezer for keeping things cold when boondocking and running on solar.

I already have a chest freezer in the trailer I tow behind my bus. It is an EdgeStar FP861. This is an 86 quart capacity freezer that runs on either 115 volts AC, or 12/24 volts DC. I have always run it on AC as I am primarily connected to shore power, but I did some further checking and found that it may actually be much more efficient to run it on the 12 volt DC supplied from my battery bank. Total distance from my batteries to the freezer is approximately 12-15 feet. Here are the figures from the label on the back of the freezer.

AC 115 volts 1.0 Amps
DC 12 volts 5.5 Amps

According to my calculation this is 115 watts on AC power compared to 66 watts on 12 volt DC power. The label on the back of the freezer also has a watt rating of 80 watts. I am not sure how this is calculated, or whether it relates to AC or DC power usage.

Please correct me if I am wrong, as I am assuming that my overall power consumption would be far less using DC power, and therefore I would use less overall watts by powering the freezer with 12 volt DC. The only way I see that DC might not be more efficient, is if the compressor takes longer to cool the freezer when running on DC. If DC power cools slower, actual power usage may equal out with AC power consumption.

Unless I am advised otherwise, my plan is to not use the Dometic refrigerator in my bus when boondocking. It will make a nice pantry to store various dry goods. I will then use the EdgeStar chest freezer powered on 12 volt from my battery bank for all cooling. It has an adjustable digital thermostat so it can be used as a refrigerator or freezer.

• Banned Posts: 17,615✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

Well an absorption 'frige when run from AC merely replaces the propane flame with an electric heating element. That's why it's not so great.

Do not trust numbers on tags. Plug it in with a Kill-A-Watt and see what that freezer really uses. Likewise it would be good to check the actual DC current. If this unit has a DC motor which is run through a power supply when operated off AC then it likely is more efficient on DC.

When it comes to making a 'raw choice' between a DC refrigerator or a standard AC one you need to compare cost differences between the two (DC almost always more expensive) for both volume of the unit and how much more system power the higher cost could pay for. Quite often it's pretty easy, like a \$500 off-the-floor household AC unit vs. a \$2500 DC unit - that is half the capacity. \$2,000 can buy a lot of solar power. But this is not always the case.
• Solar Expert Posts: 494✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

It could be the AC rating is for more watts because there are losses in converting the 120 VAC to 12 VDC. I believe that unit has a Chinese made danfoss type 12 volt compressor. The danfoss are very efficient. We have a 12 VDC 4.something cu. ft. 'Truckfridge'.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Registered Users Posts: 21
Re: Refrigerator Considerations - AC or DC wiring
Do not trust numbers on tags. Plug it in with a Kill-A-Watt and see what that freezer really uses. Likewise it would be good to check the actual DC current. If this unit has a DC motor which is run through a power supply when operated off AC then it likely is more efficient on DC.

When it comes to making a 'raw choice' between a DC refrigerator or a standard AC one you need to compare cost differences between the two (DC almost always more expensive) for both volume of the unit and how much more system power the higher cost could pay for. Quite often it's pretty easy, like a \$500 off-the-floor household AC unit vs. a \$2500 DC unit - that is half the capacity. \$2,000 can buy a lot of solar power. But this is not always the case.

Once I get my solar auxiliary system revamped and up and running, I will check the load on the freezer using the Trimetric 2030RV Battery Monitor that I have on hand. I can then run the freezer alternately on AC and DC and see what the difference is.

I have had this freezer for about two years. It was pricey for the capacity (about \$600 at the time of purchase), but not so exorbitant as to be able to buy a cheaper one and expand my solar array or battery bank.
• Registered Users Posts: 21
Re: Refrigerator Considerations - AC or DC wiring

Thanks Don. I generally check appliances and other significant purchases out before spending money. This particular freezer had some excellent reviews, and there are a limited number of them available that run on either AC or DC. I think overall, that running this on DC straight from the battery bank will be the most efficient. After all, there is power loss when converting DC to AC with an inverter, and it is possible that the freezer is converting the AC back to DC where power efficiency would take another hit. So my guess right now is that running it on DC will be the more efficient option.
• Solar Expert Posts: 494✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

From a downloaded Edgestar manual.... (approx half way down pages) "Note: Do not use the refrigerator-freezer as refrigerator when the ambient temperature is lower than 41°F "

From the Edgestar website...
"....Many portable freezers, such as the Edgestar FP series, also include a 110 volt power adapter so you may power the unit with a traditional wall outlet as well."

I think that pretty much means it is a 12 VDC unit with an accessory, maybe built in, to use AC. So starting with battery based DC and inverting is a waste of stored battery energy. Just my take on that.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Registered Users Posts: 21
Re: Refrigerator Considerations - AC or DC wiring

Thanks Mountain Don. The 110 volt power adapter is built right into my unit, which is the largest freezer in the Edgestar FP series. The plugs for AC and DC are right next to each other. The quote from the Edgestar website pretty well settles the matter about DC being more efficient. That was a good find.

I haven't actually used the freezer as a refrigerator, and here in Georgia there are few days when the temperature gets below 41 degrees and stays there for any significant amount of time. I suppose if the temperature did fall a person could just unplug the thing and it would stay cool by itself due to the outside temperature being chilled.
• Solar Expert Posts: 3,123✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring
From a downloaded Edgestar manual.... (approx half way down pages) "Note: Do not use the refrigerator-freezer as refrigerator when the ambient temperature is lower than 41°F "
Their concern could very well just be that the unit cannot keep from driving the interior temperature below freezing, 32°F, (a bad thing for a refrigerator!) if the ambient temperature is below 41°F.
SMA SB 3000, old BP panels.
• Solar Expert Posts: 494✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

Or it could be that the freezer food may thaw because the compressor will not need to run, or not often enough, to keep the fresh food cold. ??? If that unit operates similar to our danfoss compressor equipped truckfridge the compressor only runs when the freezer section is not cold enough to bleed 'cold' to the fresh food section. When the ambient air is quite cool the comp motor will not run much and the freezer may warm to just around freezing instead of the below freezing point. Probably have to do some tests with some remote thermometer probes inside the freezer and the frisge both.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Solar Expert Posts: 3,741✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring
inetdog wrote: »
Their concern could very well just be that the unit cannot keep from driving the interior temperature below freezing, 32°F, (a bad thing for a refrigerator!) if the ambient temperature is below 41°F.

I don't think so. The sundanzer fridges and freezers have the same issue... I have the sundanzer freezer and it won't work properly at near freezing ambient temperatures. The reason, I believe, is that the thermostat is NOT in the food compartment... it is somewhere else in the freon circuit. I think this allows for better proportional control of the compressor.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 203✭✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

There's a recent review on Amazon of the Edgestar 80 qt unit with some useful numbers, though he's using it as a refrigerator:
According to my Kill A Watt EZ meter, it draws as high as 77 watts and 1.01 amps. As it nears my target temperature of 40 F, the meter reads 72 watts and .95 amps. When the compressor is not running, the meter shows it at 5 watts, .07 amps....Using this as a fridge set at 40 degrees, my Kill A Watt EZ says it uses about .6 kWh of electricity per day....

Update: I have now checked the 12V amperage with a meter. The compressor does not peak when it first comes on. The draw begins low and then rises. Once it stabilizes, my meter shows it mainly staying between 5.5 and 5.6 amps DC. When the compressor goes off, the meter goes very low and then stabilizes to around .015 amps DC.

I'd like to see similar numbers when used as a freezer. Dreamer, if you take measurements will you please post your results? I'm looking at options to run a chest freezer and/or fridge on solar.

Re. your RV fridge, they are insanely inefficient when run on 120 VAC. I'm running my Dometic on propane. It also requires a bit of 12V power for the controller (~0.2 amps, roughly 4.5 to 5 ah/day). Don't like using propane, but don't have the \$\$\$ to expand my solar power system to run a fridge solely on solar.
• Solar Expert Posts: 494✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

Interesting numbers. Our truckfridge (4.2 cu ft) consumed 300 to 500 Wh a day this summer on a 3 week trip from NM up through and around CO. That's with some extra side, top and bottom insulation and what seemed like lots of daily door opening and closing. Not as good as a Sunfrost but not as expensive either.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Solar Expert Posts: 814✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

Thought now needs to be given to the very efficient Inverter refrigerators like the ones from Panasonic.. Initial price is a bit high but startup requirements and running power use is much lower than "standard types" .. Can make it a good candidate for solar use.
• Solar Expert Posts: 3,741✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring
john p wrote: »
Thought now needs to be given to the very efficient Inverter refrigerators like the ones from Panasonic.. Initial price is a bit high but startup requirements and running power use is much lower than "standard types" .. Can make it a good candidate for solar use.

I wonder if the new inverter fridges will match or exceed the efficiency of the DC powered Danfoss compressors (used by sunfrost, sundanzer, and many others).

For quite a few years now the Danfoss compressor has been a variable speed compressor.

It seems to me that the general consensus on this forum has been that a conventional energy-star fridge is more cost effective than a DC fridge in most off-grid homes. If these inverter fridges are as expensive as the DC fridges (and I haven't seen any prices in the US), then I suppose that a conventional fridge will remain the cost effective solution.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 814✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

This is a simple summary of a test of one we had at work.
sIZE 400L MADE OF 300L FRIDGE AND 100L FREEZER
Start up draw on 230v and 50hz ..270w.. would start almost every time first attempt on low cost consumer 300w TSW inverter
Running draw 117w
• Banned Posts: 17,615✭✭✭
Re: Refrigerator Considerations - AC or DC wiring
john p wrote: »
This is a simple summary of a test of one we had at work.
sIZE 400L MADE OF 300L FRIDGE AND 100L FREEZER
Start up draw on 230v and 50hz ..270w.. would start almost every time first attempt on low cost consumer 300w TSW inverter
Running draw 117w

Wow. That really takes the peak demand down! Usually you expect a refrigerator to pull 1000 Watts + on start-up; that one is a bit more than double the running Watts.

I wonder what the effect on the power grid would be if more (all) of the surge demands were lowered like that? Other than the obvious lack of lights dimming just because the washer is cycling.
• Solar Expert Posts: 3,741✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring
I wonder what the effect on the power grid would be if more (all) of the surge demands were lowered like that?

It would make it just a bit easier for customers to abandon the grid :roll:

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 6,841✭✭✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring
john p wrote: »
Thought now needs to be given to the very efficient Inverter refrigerators like the ones from Panasonic.. Initial price is a bit high but startup requirements and running power use is much lower than "standard types" .. Can make it a good candidate for solar use.

They do not appear (in my search) to be on this side of the pond yet. Very nice inverter based 240VAC 60 hertz 21 cu. ft model. Very low surge!
Look in the feature section on the link.

http://www.panasonic.com/in/consumer/home-appliances/refrigerators/frost-free/nr-by602xs.html

It would be interesting if the algorithm could go further and allow the user to program preference on time of day usage. It does appear to learn the user.
There is hope!
"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net

• Solar Expert Posts: 494✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

Wow, that is a nice fridge. It'll be nice to see them arrive in the USA and how the pricing compares. We're going to want a new full time fridge in a year or two.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Solar Expert Posts: 494✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

I was unclear on just what an inverter refrigerator was. So I Googled....

Samsung info

and another article
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Solar Expert Posts: 1,220✭✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

With respect to the OPs question about DC fridges, its something you have to do the numbers on. On the up side they are more effcient, for two reasons. No DC-AC-DC type multi conversion losses. and second, they "tend" to be insulated and engineered for power scarce environments.

On the down side, is what others said, less range, higher price. Obviously a niche application is in roof size constrained applicatons like boats and RVs, where the maxim 'cheaper to just buy more PV' does not apply.
1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Registered Users Posts: 21
Re: Refrigerator Considerations - AC or DC wiring

Hello Plowman. That is some useful information you found online regarding the Edgestar freezer.

"According to my Kill A Watt EZ meter, it draws as high as 77 watts and 1.01 amps. As it nears my target temperature of 40 F, the meter reads 72 watts and .95 amps. When the compressor is not running, the meter shows it at 5 watts, .07 amps....Using this as a fridge set at 40 degrees, my Kill A Watt EZ says it uses about .6 kWh of electricity per day....

Update: I have now checked the 12V amperage with a meter. The compressor does not peak when it first comes on. The draw begins low and then rises. Once it stabilizes, my meter shows it mainly staying between 5.5 and 5.6 amps DC. When the compressor goes off, the meter goes very low and then stabilizes to around .015 amps DC
."

These freezers generally cycle on and off based on about a 5-7 degree temperature range. They can be set as low as -8 degrees Fahrenheit which is 40 degrees below freezing. I have my low temp set to 19 degrees and it rises to about 24 degrees before the compressor kicks on. It doesn't take it very long to cool back down and cut off, even in the middle of a Georgia summer. I have been running it on 110 AC power, however, so I will have to see if I get the same results when running it on 12 volt DC. I do anticipate that it will be more efficient on DC power regardless. If I am able to get the figures when I have it wired to DC and on a monitor, I will try to post the numbers.
• Solar Expert Posts: 814✭✭✭
Re: Refrigerator Considerations - AC or DC wiring

Anyone interested. If you are in the market for new air con . Buy a split type inverter one. The savings are unbelievable. We have them installed now in most of the house.. To give example the 1hp one for each bedroom consume 80kwh a month that's running 10 hrs a night.. Our previous window air cons 3/4 hp consumed about 200kwh a month each.. And were noisy even when new. the new ones you can hardly hear them.. Out night time temps here are between 20degc on very ""cold""" winters night and 30 deg c.on most nights of the year..