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Inverter
#1
I have 2 100ah house batteries (not lithium). I have a small Danby 4.7 cu ft refrigerator. I want to put in an inverter for the refrigerator when traveling/when the power is out and possibly run another thing here and there if needed if the power is out. But the inverter will sit by the refrigerator. What size inverter would I need? Pure sine wave? Preferred brand or does it matter? Do I need something else? Battery manager or something? There is no solar. Even though my plan is to sell the RV, I want to buy the right thing as if I'd keep the RV for a long time so not "the bare minimum" to do the job.

There's no info on the paperwork for my fridge on how many watts and it's raining so I can't check the back of it right now. I can tell you that they've almost doubled in price since I bought one. Good grief!
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#2
> I have 2 100ah house batteries (not lithium). .. There is no solar.

How are they charged?  It's really hard to keep lead batteries healthy without solar or shore power.

> I have a small Danby 4.7 cu ft refrigerator. ....

(pdf) suggests 331kWh/year, or 907Wh/day.  If correct, it's a hungry fridge.  Assuming we can use 50% of the 200Ah we have about 1,200Wh usable capacity.  After inverter 10% (probably low) we are probably at 998Wh/day.

A seller on Amazon says:  "a power input of approximately 1.3 running amps. Please note that start up amps can by up to 6 times the running amps. " 1.3A would be 156w, and 6x startup spike could be as high as 936w.  So I'd think a 1000w PSW inverter could swing it if that's all we are running. 

You didn't ask this question, but IMO this fridge would be a bear to run off a battery bank.

> I want to put in an inverter for the refrigerator when traveling/when the power is out and possibly run another thing here and there if needed if the power is out. But the inverter will sit by the refrigerator. What size inverter would I need?

Add the wattage of any "here and there"  things to the fridge's 936w startup to find total size needed.

> Pure sine wave?

The compressor would prefer PSW, in my opinion.

> I want to buy the right thing as if I'd keep the RV for a long time so not "the bare minimum" to do the job.

Most people who offgrid in older RVs use three-way fridges on propane, or very efficient compressor fridges and solar.  Those of us in vans typically use small compressor fridges run off solar.   The Danby is 6.5x the capacity of the one I use.   And several times the power consumption.
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frater/jason - FT 2018.  Retired/boondocking 2020.  
159" Promaster, 570w:220Ah, 35gal fresh
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  • Kyz (01-20-2023)
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#3
You could just use the generator ....but since you asked....

The maximum start up current for whatever devices plugged it at the same time will govern the size of inverter. It should be placed as close to those batteries as possible . The more powerful the inverter is the beefier the wires will have to be and the size goes up real fast every extra foot it's away from the batteries. AC power travels much more happily on much smaller wires but they are amp rated too...

A device called a KILL A WATT . A little plug in meter that goes in a 120v outlet and displays the volts , watts and amps (and records current used over time )of whatever you want to measure such things on.~$20-30 at an Ace etc. (some libraries have them to loan)

Don't forget fuses/breakers.

Most inverters have low voltage cut off built in..

Pure Sine Wave produce power the most like the power company . Best for electronics....If all you want to run is a hotplate just get a MSW cheapo . But you have a gas rangetop.
Almost every Rver I know buys PSW I have a 700watt one but also have a Honda 2000 for more power hungry stuff.


The batteries will decide how long you can go between charging but charging should be done asap and completely not just till they come up to voltage but till amps going in are very low (like below 1 amp) Every day if possible.
Alternator charging for while traveling with a solenoid /etc. would be a good accessory to have .

Victron or Renogy seem to be the most popular brands lately.

The trick with lead batteries is don't use more power than you can replace the next day,,,while driving or plugged in somewhere.
stay tuned 
popeye


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  • Kyz (01-20-2023)
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#4
I'm on shore power most of the time. If I wasn't, I'd run the generator as needed (power outage) or I would be driving to a location with shore power. It does have alternator charging.

Thanks for all the information. I had thought I'd get the same refrigerator if I get a van, but I'll nix that idea.
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#5
I'll stick with a 1000w PSW inverter and skip the "here and there" charging.
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#6
The start up surge rating of inverter A and inverter B, might be the same, but a might handle.500 millisecondes and B might handle.1000 milliseconds

The inverter might start the fridge compressor.fine at 65f ambient, but not at 55f ambient.
Ive read about going just big enough on inverters for ac residental fridges and then having to get larger and larger inverters till it worked properly, reliably.

If this is only for when driving from a to b, and they are not 10 hours apart...perhaps dont even bother, just crank it up a few hours before leaving, and keep door shut.
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#7
I've used my fridge on AC from the campsite and generator but IIRC never ran it off the inverter.
It made more sense to just plug it into DC. And no loss from the extra conversion. But a residential fridge would need an inverter .Or like SW said just don't open it after you drive off.
stay tuned 
popeye


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#8
Back in the dark ages of the 90's to the mid 2000's. I used to buy a couple of 'bricks' of dry ice at the grocery stores and pop those in the pre-chilled freezer and fridge compartments of the RV fridge, and that would last at least a day, sometimes two days.

The last few times I've tried to find dry ice, the sub-30 year old employees just shrug and say...nope..or what's 'dry ice'?

But if you can find it, it works well for a day or two of traveling with perishables in the fridge.
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  • rvpopeye (01-20-2023)
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