I'm thinking of using an AC fridge instead of DC. How much less efficient is an AC fridge with an inverter compared to a

magentawave · May 2, 2013

I'm going to be living and traveling in my 18' Toyota Sunrader motorhome when I'm done rebuilding it and I need a lot more space than the silly little stock fridge holds. I'm thinking of buying an AC only "apartment" fridge/freezer and run it with an inverter in my  motorhome. (I don't want a propane fridge and I don't want to spend a fortune on a DC fridge.) I'm going to have about 250 watts of solar with probably 3 house batteries. I have a couple questions please... 1) How much less efficient percentage wise is an AC only fridge running off an inverter compared to running a DC fridge? 2) The opening width of the side door on my Toyota motorhome is only XX" wide (Can't find the measurement now!) so I'm wondering how the heck I'd get a larger fridge in there since most of the apartment fridge freezers are around 21" to 22" wide? Since I'm doing a major remodel of my Sunrader anyway I was thinking I could make it so the back window could be removed so I can get the fridge in and take it out if I have to.  Has anyone replaced their little stock fridge with a tall narrow AC fridge/freezer? Or how about making the large back window be removable? Any ideas will be appreciated please? Thanks Steve

psytechguy · May 3, 2013

It sorta depends on the inverter. Some are more efficient than others (and more expensive) but there is always a loss.

See:

http://www.solar-facts.com/inverters/inverter-efficiency.php

James AKA Lynx · May 3, 2013

Depends on the fridge, The high efficiency DC frig's have a great motor that requires less amps. Buy the good DC and us AC when needed. Propaine will last longer than your batteries. James AKA Lynx

blars · May 3, 2013

Ofhand, I'd guess a dorm fridge would use around 10 times as much power as a DC fridge, very different compromises.   Does your rig have an emergency exit window that could be used to get it in?  or you could remove/relpace a window.

wagoneer · May 3, 2013

My personal point of view is how many things do you really really need to keep cold. I think the reason they make those doors so small is a hint. 3 cubic ft. Propane chest. Man is one of the only mammals that consume milk weaned. OK I use it for my coffee.

highdesertranger · May 3, 2013

there is a huge difference in power consumption between a 120v and a 12v.  those small dorm refers are the worst they might be better than they used to be but are still way off from 12v.  I know this first hand.  I tried a dorm frig when trying to get off the ice chest.   huge power consumer.  this is not even counting the loss though an inverter.  sorry I don't have numbers to back up my theory only real world experience.  btw wagoneer even though I am not a big milk drinker most mammals will drink milk if given the chance even herbivores.  highdesertranger

wrcsixeight · May 4, 2013

If you buy a residential fridge with the energy star label, then perhaps it will use twice the battery power of a DC fridge. Some of the ones available are made extremely poorly with no thought toward efficiency at all.  Without the energy star anywhere from 2 to 10 times as much. The start up current on a fridge requires an inverter with plenty of capacity, like a 1200 watt inverter with double that surge.  The inverter should have a standby mode so that it uses very little power when the fridge compressor is not running. Mine does not have this feature, and draws 0.9 amps turned on, powering nothing.  That is more than my Compressor fridge uses most hours. Another consideration is road vibrations.  Residential fridges were not designed to deal with speed bumps and pot holes.  The lines containing the refrigerant can get brittle and crack from flexing.  Another is that some sort of locking mechanism will have to be fitted to keep the door from opening on its own during left turns. The price of a DC compressor fridge is high, but it is cheaper than buying a residential fridge, then later new batteries and a DC fridge anyway. Window removal is the common way of replacing a fridge too big to fit through the door. You can make a residential fridge work, you will just need more solar and more battery, and there go the savings over buying a DC compressor fridge to start with.  If you are plugging in when parked then a residential fridge will be just fine.  If you are overnighting without hookups then I recommend getting a Danfoss powered 12v dc fridge as these are the most efficient fridges on the planet.

Les H · May 5, 2013

Someone will have to help with the math ( inverter losses etc) , but the ac only fridge that someone put in my 5 th wheel drew. 9 ( point nine) amps at 115 vacate. I gave it away and put in a 3 way fridge because I wanted the versitility a three way offers. The plate on the 3 way says it draws 8 amps Dick. One thing to consider is that an ac dorm fridge will only run 30-40% of the time vs 100% on for a 3 way. A dorm fridge and decent inverter will be about $150. A used 3 way is about $150 if you can find one, the smallest one new is around $500. A dc only fridge like a Dometic or Engle. Is about $500. The cost difference will buy more solar panels, batteries, or an inexpensive generator. What will your budget allow?

Willy · May 5, 2013

 Years ago, when I bought my (used) '75 Winnie, it came with a small 115v AC fridge that had been swapped in. Tried running it off an inverter w. 2 deep cycle batteries and 45W solar.. killed the batteries in no time and might as well not have had ANY solar for all the good it did. Forward a few years and that same 45W of solar and 1 battery and my Waeco cooler had everything in (meat) literal deep freeze for a month and the batteryin good shape. ..Willy.

highdesertranger · May 5, 2013

ok so .9 amps at 115 = 9amps(appox) at 12v.  plus the loss though the inverter so you are over the 3 way.  absorption refrigerators(3 way) are very inefficient running off electric.  imho they are inefficient on propane also because you are still consuming propane that will eventually run out and have to be replaced.  so then you have to consider the gas and time it takes to go get the propane into the equation.  I have used all the refers while camping 3 way, 120v, and 12v.   imho there is no comparison 12vhas them all beat for efficiency,  hands down.  highdesertranger

Willy · May 6, 2013

 And, don't forget, those lousy POS absorption fridges really don't like being off-level (do a lot of boondocking?) and have an open flame. I wonder how many people forget to turn the gas off when driving and then go to fill up. Another is having it switched to 12v and.. forgetting. ..Willy.

IGBT · May 6, 2013

Actually the absorption refrigerators knock the socks off 12V refrigerators because of the energy density of propane vs a lead acid battery.  A gallon of propane has an energy density of about 90 megajoules A 100 amp-hour 12V lead acid battery has a maximum energy density of (100 amps x 12V = 1200 watt-hours = 4.32 megajoules So a typical deep cycle battery drained heavily has 1/20 the energy content of a single gallon of propane. A 5 gallon cylinder of propane is about the size of three deep cycle batteries, so for the same size (and a lot more weight!) the three batteries have about 1/30 the energy content of a 5 gallon cylinder. Perhaps this is why you can run a typical 3 way fridge on 5 gallons of propane for 2 months!

Willy · May 6, 2013

Well, the energy density of propane might be higher than that of a battery, but the sun (solar power) has propane beat, hands down. With the price of solar getting so damned cheap, propane's lookin' worse 'n worse in comparison. One thing I'd like to mention is the sometimes abysmal quality of 'RV' accessories, at sky high prices too. ..Willy.

IGBT · May 6, 2013

yeah, if you can get the sun, solar and a 12V compressor fridge would be the way to go.  If you are spending much time in the Northwest or up in Alaska, solar will be all but useless.

Noah · May 6, 2013

I agree with Wagoneer.  I have a small dorm fridge in my rig with the idea of using when I have full hookups, but never actually have.  It just stores my food and keeps the temp at least somewhat regulated.  I use instant dry milk for my cocoa and pasta dishes,  eggs will keep for at least a week, probably more without refrigeration,  fruits and veggies get several days, and the rest is a treat when I can eat it right after buying it from the store. I will say that I miss ice cream and cold cereal, but they aren't worth the headache of providing so much energy to keep it cold. In certain parts of the world, they just sit their perishables outside the window if the climate is right! I'm always surprised when the first question people ask me is how I keep my food cold... I never considered it much of a big deal.

highdesertranger · May 6, 2013

well I am in the pacific northwest every year and have spent time in Alaska.  solar has always worked for me.  not saying it would work in coldfoot in the middle of winter but in the summer I works just fine.  after the initial investment you are done.  propane always runs out sooner or later,  the sun will always rise tomorrow.  maybe not for everybody, but it has been the single best investment for me as far as being able to stay out in the field for long periods of time.  on the other end,  if you are in an area of high daytime temps you are going to eat though that propane pretty darn fast.  I know this from experience too.  highdesertranger

CrossCountryGal · May 6, 2013

Long term efficiency and costs were not my first consideration.  Minimal outlay of upfront cash was.  On hand I owned one of the larger, taller dorm fridges and a Honda generator so I'm using those.  I don't live in my bus, but take extended road trips in it (2-6 weeks) This is the first trip I'm using the fridge and it's running a gallon of gas a day, which is a bit pricier than the cost of ice, but I can stay off grid for longer since I have 10 gallons of dedicated gasoline for the generator.  I'm actually saving money because I can stay in a more remote location since I don't have to replace ice every couple of days. The 1 gallon of gas the generator burns daily also keeps my laptop, iPad,and iPhone charged, runs my music/docking station, and occasionally a lamp with a traditional light bulb. Not the best solution, but workable for me.

Willy · May 7, 2013

 I'm up in Canadia here and, even when I went up north, there was plenty of solar for my needs. If I were to head up into the Yukon 'n such then, yeah, wouldn't be enuf solar in the winter to run a fridge.. but at -50 deg, who needs a fridge? ..Willy.

highdesertranger · May 8, 2013

ha ha willy then you need a heater to defrost your stuff.  country gal out hear in the desert the price of a gallon of gas won't buy you much ice in the summer,  people that sell frozen water are pirates.  sounds like your doing fine with your set up.  I still want one of those gens.  maybe next year.  highdesertranger

Zil · May 9, 2013

Just wondering? If CCGal used a battery to run the fridge, which is off as much as on due to thermostat, then charge the battery with generator, less run time on generator uses less gasoline?