Group 27 deep cycle battery + 2000W inverter

You generally don't need more than a 1000 watt inverter to power a fridge. But if you are going to press an inverter close to 2000 watts for an extended period... 400 amp hours is barely making it. Certainly a fridge does not even come close to that with just a short surge and a couple hundred watts running.

Gdetrailer wrote:

A lot of "assumptions" being made..

2Kw inverter doesn't "need" 400Ahr of "battery support" (what ever THAT means).. If you mean 400Ahr capacity, you would be dead wrong because the OP did not specify just how long are they needing to run the fridge from inverter..

Well yes. poor choice of words

Xantrex recommends two pair GC-2 for a 2000 watt inverter is what I should have said. Yes it will work on less. but Xantrex recommendation for the Prosione 2.0 was 2 pair GC-2 or 420 Amp Hour. of storage

Not enough information to hazard a guess.

That being said, I have run a ten year old (not very efficient compared to new ones), 14 cubic foot (smallish “full size”), refrigerator for several days in 75-85 degree ambient temperatures and measured electricity consumption to be 2.0 kilowatt hours per day. Newer, more efficient refrigerators, larger/smaller ones, warmer/cooler environments, all make a difference. Oh, add 10% to cover the inverter.

That’s my beer fridge down in my man cave. 2.2 kWh translates to 183.33 Amp-hours, requiring 4.3 (that is, actually 5) of the common group 27 “marine deep cycle” batteries most travel trailers come with. Your mileage will vary, depending on factors noted above.

wa8yxm wrote:
If you are lucky .... an hour Likely less

That inverter needs 400 amp hours of battery support
two pair of GC-2 is recommended.. That's 400 amp hours with 200 usable
your group 27 is 100 (bit less) with 20-25 usable.

The fridge.. Well you did not say but look at the watts and divide by 10. yes 10 that's how many amp hours it will suck off the battery. So if it sucks 200 watts then it needs 20 amps of battery power

Both Dometic. and Norcold at one time made RV-Fridges using a ultra-high effiency compressors. 35-40 watts.. at 12 volts that's a bit over 3 amps. Door closed (Seems strange to have to specify door closed but the interior light adds a major draw)

A lot of "assumptions" being made..

2Kw inverter doesn't "need" 400Ahr of "battery support" (what ever THAT means).. If you mean 400Ahr capacity, you would be dead wrong because the OP did not specify just how long are they needing to run the fridge from inverter..

As I mentioned in my other post above, inverter will draw an average of 1Ahr-2Ahr per hr the inverter is turned on. 24 hrs of that and that is 24Ar-48hrs of battery not including fridge or anything else.. That certainly is not anywhere near 400Ahrs of "support".

Many apartment sized residential fridges will use about 90W at 120V and typical run time will be 20 minutes-30 minutes per hr..

So, lets say the fridge runs 30 minutes per hr at 90W level..

That is 7.5A at 12V (90W) x 12 (run time of 30 on and 30 off for 24 hrs) = 90Ahr

Add in the inverter loss (total time on, plus time with fridge running) of 48Ahr.

And we get 138Ahr of battery capacity required for the inverter and fridge for a 24 hr period..

Far less than your "assumed" 400Ahr of "support"..

Even if you went went with a far bigger fridge the results most likely will never come close to the supposed 400Ahr "support" you claimed..

And for the record, I AM using just ONE PAIR of 6V GC2s with a home fridge conversion.. ONE PAIR of GC2 gives me plenty of capacity to run my fridge for 24hrs, plus run the 30K furnace plus a few hrs in the evening of using lights and STILL have plenty of battery capacity left over..

Since the OP did not say how long they NEED to run the fridge and how much current the fridge uses plus details on the inverter and how much no load power it uses absolutely no way to blanketly say that the OP needs so much capacity "support"..

My suggestion is the OP should try their current battery in their driveway without shore power to see how long it runs.. Then they can make a better decision on how long they wish it to run and how much battery they will need for THEIR use.

Much better than giving some hokey number you pulled out of a hat because YOU don't like Home fridges in a RV..

Not everything must say RV on it to be used in a RV..

Running time on the one battery will be short as everyone noted. Another thing is with the inverter, you have the low voltage alarm and shut off, which could be triggered by the fridge when it cycles.

You need short fat wires from inverter to battery, and a decent size battery in AH (or one of the new ones that allow high amp draws and keep their voltages up) to handle the fridge's starting surge.

So you could have what seems like lots of battery left in the 27, but the inverter kicks out anyway.

Most residential refrigerators that I have measured use about 1.5 kWh per day. If you only drain the group 27 battery to 50% you'll have about .6 kWh to work with. So, my best estimate is that it will run it for about half a day before it needs recharging.

As pointed out a group 27 is not much of a battery. A pair of group 31s, a pair of 6V GC or a single 4D will be needed to provide necessary AHs to run the fridge for a usable length of time.

If you are lucky .... an hour Likely less

That inverter needs 400 amp hours of battery support
two pair of GC-2 is recommended.. That's 400 amp hours with 200 usable
your group 27 is 100 (bit less) with 20-25 usable.

The fridge.. Well you did not say but look at the watts and divide by 10. yes 10 that's how many amp hours it will suck off the battery. So if it sucks 200 watts then it needs 20 amps of battery power

Both Dometic. and Norcold at one time made RV-Fridges using a ultra-high effiency compressors. 35-40 watts.. at 12 volts that's a bit over 3 amps. Door closed (Seems strange to have to specify door closed but the interior light adds a major draw)

Bear in mind that if you draw the battery down below a 50 percent state of charge, you are damaging the battery. (I don't know how much it damages the battery, but that is what they say.) So although the battery might be adequate in the short run, it might not be worth the cost in terms of reduced battery life.

Group 31 batteries have a lot more capacity and are about the same size as a Group 27. Much heavier, though -- lifting them in and out of the battery box is great exercise!! ;)

For a rough idea, look at the energy star guide for the fridge and see what it says the energy usage per day is. Many are somewhere around 1 kWh per day, very roughly speaking. (I think they give it per year, but it's easy enough to divide by 365 to get the usage per day.)

1 kWh is equivalent to about 83 Ah at 12V. To the fridge's usage, the conversion inefficiency of the inverter needs to be added. Overnight should generally be doable absent any other significant 12V loads, but probably not much more. Deeply discharging a lead-acid battery is pretty rough on it and doesn't lead to its having a long lifespan. Leaving it discharged is doubly harsh.