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Old 06-06-2023, 06:51 PM   #1
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Running fridge on inverter/batteries - how long?

We have never boondocked before & are taking a run to WY/CO which will entail some off-grid time - especially when we leave the coach early AM to go exploring & may not be back until the evening. What's a realistic expectation for fridge run time on inverter/batteries?

We just installed a new whirlpool side-by-side fridge (hopefully much more efficient than the old one), 8 6V 220AH house batteries that appear to be in great shape & a 2800 watt pure sine wave inverter.

Is there any way to get a rough idea of approximate run time b/f having to kick on the generator? Thanks
Mark & Kim
2006 Monaco Dynasty Diamond VI
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Old 06-06-2023, 07:33 PM   #2
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What is the amp usage of that Whirlpool?

Turn it on while at home and do a test run on batteries

220 AH at 6 amp = roughly 30 hours of run time
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Old 06-06-2023, 07:44 PM   #3
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I have four 6 volt batteries ~460 amp but have 325 watt of solar. So during the day in full sun the solar almost keeps up.

At night go to bed with batteries at ~90% and 8 hour later I have ~70-75% battery.

Haven't got to give it a good test but I installed a Victron BMV712 which provides good info on battery level and usage.
Jim J
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Old 06-06-2023, 07:45 PM   #4
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The answer is that depends.
Most of these residential refrigerators run a low duty cycle IF the doors are not opened frequently, and they are not in a hot environment.
Some experts will tell you not to run your batteries below 50%.
Most of the time we get about 12-24 hours with our Samsung.

If you have an auto gen start you can set it to come on when the batteries get low.
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Old 06-06-2023, 07:58 PM   #5
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With eight 6V 220AH batteries, assuming they are charged, you should have no problem for those 12-18 hours you are away from your RV.
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Old 06-07-2023, 01:01 AM   #6
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The first day will be no problem… you will have plenty of power as long as you aren’t wasteful with the power.

The trick is to get enough power back into the batteries for the second, third, and more nights. I would HIGHLY recommend a Victron Smartshunt or BMV712 (or other shunt based battery monitor). One of the best features of the Victron products is they have a “Remaining Time”.

It has a few assumptions… if the power in the last 5 minutes stays constant then the batteries will last _____ hours until they reach the Discharge Floor (user setable) For lead batteries usually 50% - my lithium’s are 10%. Currently I have 1day 14hrs until I reach that floor.

The battery monitor also helps you make sure you get enough amps into your battery that they really are charged.

With a residential fridge- I would highly recommend a real solar array for the roof. It just makes it nice knowing that the rig will recharge (or mostly recharge) the battery- as long as you get good sun. (And solar prices have dropped a lot!)

Good Luck
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Old 06-08-2023, 11:13 AM   #7
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With 8 batteries, two days easily. But make sure you run the generator a good 4 to six hours if you run them down. On the aladdin just look at your battery voltage when you get home, if it's below 12.4 with no load (refer not running) then you need some longer gen times, ( again, the aladdin will show when your sitting voltage is back up to 12.7 with a slight draw, like tv, lights. Not sure you have the aladdin but monaco certainly put in a monitoring system in your coach like silverleaf etc. I consider 12 volts at rest completely run down. The xantrex control panel should also show house voltage. But I stick with one or the other after having confirmed it once with my actual voltage at the batteries.
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Old 06-13-2023, 03:36 PM   #8
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Well I second the man who said it depends

There are a lot of variables. 6 volt batteries that look good means very little because you can destroy a set of batteries in very short order if you're not managing them well.

I second the man who said charge it up in your driveway and run it overnight and see what happens. I'm so spoiled with shunt measurements of actual usage that I don't even remember the numbers now on state of charge for lead acid batteries but my memory is that topped off the coach voltage should be about 12.6 or 12.8 after everything is turned off and they arrested for a couple of hours and that would indicate Good batteries. Then whatever the total rating of your battery pack is in amps divide that by 2 and certainly with brand new batteries, that's how much useful power you're going to have before voltage drops below 12 volts.

Also running a victron power measurement system is a great idea. A piece of 2-0 cable as a jumper and a little bit of skill and you can install a victron 500 amp smart shunt quite easily in most situations. Calibrate that and you'll really know what's going on with your batteries.

As another driveway check I have a couple of plugins called Kill A Watt meters tell you the AC line voltage the cycle rate IE 60 cycles per second or any variation as well as current wattage flow current amperage flow and accumulated amperage usage.

When I have to know what an appliance is doing to me I plugged that thing in for 24 hours and come back and find out how much that appliance has really consumed. It only requires that you get through the inspection panel and into the back of the fridge so you can unplug it from the outlet and plug it in to the meter and then plug the meter into the outlet.

Then to really frustrate people let's have a quick discussion about current. Something that is using for amps at 120 volts is going to be using about 40 amps of battery back at the inverter. That's just a crude rule of thumb and you can shoot it all to pieces with this variable and that variable and this efficiency rate but it's a good rule of thumb.

When I was on a trip where my gas electric refrigerator could not be run on gas and had to be run on electric I learned that a norcold 1200 pulls between 4 and 4 and 1/2 amps AC and that turns into roughly 40 or 41 amps being pulled by the batteries to power my inverter for every minute it was turned on

And yes an automatic gen start is the magic pill but of course I don't have one.
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Old 06-13-2023, 06:41 PM   #9
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I will add another vote for running it in the driveway, unplugged of course, to see how long you can go....
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Old 06-13-2023, 11:47 PM   #10
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For about 5 yrs now I have been boondocking with a Samsung frig, 600amp hrs of battery, and 650 watts of solar. Typically, the coach runs on the sun during the day but starts to draw down at sunset. In the evening, Iíll run the generator to bring the charge to full before bed (1 to 2 hrs). Overnight the frig will cool and make ice and other things like fantastic fans and maybe a ceiling fan over the bed will run all night. By morning the battery bank will be about 60% full. Will run the gen if cooking with the microwave and then the sun takes over and the cycle repeats itself. Cloudy days means more time. An automatic gen start is invaluable if you are away from the coach for an extended period or if you have to lock up your pet for a few hrs. My auto gen start can be set to come on either at a low voltage point or when the coach temp rises to a set point to allow ac to run. Worth its weight in gold.
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Old 06-14-2023, 06:11 AM   #11
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Thank you all for the outstanding feedback - truly appreciated!

We do have AGS on our Dynasty. However, our generator will not start unless the coach motor is running. It attempts to start w/o the engine running but only gives us a couple grunts. I've checked some of the grounds but haven't completed the process. Hopefully I can nail it down & then we'll have AGS.

Thanks again!
Mark & Kim
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Old 06-14-2023, 08:25 AM   #12
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Originally Posted by Stan&Jacquie View Post
... Overnight the frig will cool and make ice and other things like fantastic fans and maybe a ceiling fan over the bed will run all night. ....
Slightly off topic, but Stan's comment reminded me... My fridge (and I assume all residential fridges) uses a lot less power with the icemaker turned off.
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Old 06-14-2023, 11:33 PM   #13
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My own experiences with a residential refrigerator in my 2011 40 foot Monaco Knight and the refrigerator being of the same vintage I will assume at the moment. I started buying it used with 4 deep cycle marine batteries and boondocking for weeks at a time and quickly discovered half of them beyond repair. I can't say whether they bad from the beginning or the loads just got to them. Replaced two of the four and good for a a few days then the other two seemed to go bad. Anyway, I went round and round with these flooded battery types with charging a couple hours in the morning and a couple in the evening with a generator mind you as i have no solar and too busy in the day to be hanging around letting the generator build them up. But it just seemed too much for the batteries I had....I would wake up every morning with my batteries so dead I'd have to jump start them to start the generator and of course everything else dead that depended on the inverter. Since then I bought two 100 amp Lithium batteries but soon discovered even that was not quite enough for boondocking in Quartzite AZ for the month of January. So bought one more for a total of 300 amp hours of lithium. That seems to work fine but still need to run the generator a couple hours in the morning and evening to keep things alive. I do watch some tv in the evenings maybe a couple hours and use the microwave very little but that fridge and any residential is a hog!
Hope this helps a bit..
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