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Discussion Starter · #1 ·
Ok so my refrigerator in my camper took a crap and instead of buying a propane one I thought about this. Couldn’t I buy a 120 volt one and run it off an inverter connected to two deep cycle batteries? The batteries have a rating of 140 min @ 25 amps per hour X 2 is 280 min @ 25 amp hour. When you hook it up to an inverter does it just change the 12 volt DC batteries into 120volt AC and keep the same reserve capacity of 280 min @ 25 amps if that the case fallow my math. The fridge is 1.3 amps. 1.3amps divided by 25amps=19.23 times longer than at 25 amps. So 280 min reserve capacity times 19.23 times longer = 5404 min or 90.06 hours or 3.75 days of run time. Is this right or did I just completely over think this one???
 

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No I don't think that's right but I can't tell you why. Hopefully an electrician will chime in soon. If not, post this up on an RV forum. I would love to hear the answer.
 

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A couple things to consider
120 volts ac * 1.3 amps = 156 watts.
156 watts/12 vdc = 13 amps dc

So if you inverter were 100% efficient (its not) a single battery would last about 4 hours if the frig ram continuously . You may be able to use AGM ($$$) batteries to get longer life. Look at the amp hour rating of the battery to determine how long it will run. Atypical trolling motor battery is rated about 140 amp hours. Divide 140 by the amount of dc amps will give you a crude idea of battery life. Lots of other factors but this will get you
Close. Also note the inverter efficiency could be pretty poor (~50%) which cuts the battery life by half. Finally I'm not sure but the in inverter probably puts out a square wave instead of sine wave which would be hard in the frig motor. you may be better off biting the bullet for gas. If you go with the inverter please post your results.
 

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Also keep in mind the amps needed to "start up" the refridgerator compared to just keeping it running. I ran a similar set up to what you're describing with a large 6500w inverter in an enclosed MX trailer. It worked great for smaller things like lights, radios, crock pots, water pumps etc. but I could not run my air compressor due to the required start up amps of the motor, it would trip the internal breaker in the inverter every time.
 

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Discussion Starter · #5 ·
Ok so if i do the math i would do 280 min reserve capasity divided by 13 DC amps would be 21.54 i would hope that would be in hours. If that be the caes i dont think that it would be worth going to all electric.
 

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A block of ice works pretty good and you can make it yourself cheap.;)
 

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AZ_Hunter
I'm confused by "140 min @ 25 amps per hour." Two time periods here. I'm guessing that the rating is 140 minutes with a dc load of 25 amps. To convert to amp hours (140/60) = 2.33 hours * 25 amps = 58.33 amp hours(amp hours is a common battery rating). This rating seems low for a deep cycle unless you are usinig a gelled acid type battery.

Anyway once you convert to amp hours you simply divide that amount by 13.3 then multiply by the efficiency of the inverter. For arguments sake let's say the inverter efficiency is 80%

Life for a 58.33 amp hour battery loaded at 13 amps would be (58.33/13.3) * .8 =3.5 Hours Two batteries would get you ~7.

A 140 amp hour battery would get you 8.42, 2 would be 16.

There are also some curves that come into play when battery get close to full discharge that will probably negatively affect the amount of run time.

Also note that the inverter takes power even if the appliance is off.

Disclaimer: This advice is guaranteed for the exact amountpaid:)

Good luck,
 

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FWIW I did a conversion on a 32 race car trailer and slit it in 1/2 to 16' garage and 16' living. Anyway we put in one of those small college size units. We did run it off the inverter and it did fine. The inverter was not cheap 2-3 hundred and I also ran 4 6 volt batterys. Not sure what you are doing with it. but colaw rv salvage has some used stuff as well as fleebay and craigslist. Our current one runs on 120 or propane. We also run a gen to have Air conditioning if no plug in avail.
 

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what would the conversion cost be compared to a new gas fridge? Batteries wiring switches inverter?
 
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