Inverter/Battery needs for Residential refrige

Romer1 wrote:
Will be replacing my dead Norcold N821 with a 9.8 cu ft residential in 2 weeks. Refrige draws 6.0amps/690 watts on start and 2.5amps/287.5 watts running. Planning on a 1200 watt PSW inverter which will handle load . Question is how much battery do I need?

Romer1 wrote:
Currently have 2 automotive batteries, not sure of size. That was my question, what size (amp- hour) would I need.Undrstand the 2.5 amps per hour, but refrige doesn't run continuously.

As long as you limit your off-grid usage you should be fine as is with two batteries and 1200w psw. You can still stop for lunch and take your time at some tourist spot to explore enroute.

If you plan to overnight without utility power you will be pushing the pair pretty hard if no generator use. I would go 4x golf car batteries. If going extended camping off-grid I would be at 6x battery and 600+ watts solar... Maybe lithium battery.

Boon Docker wrote:
That is a pretty crappy fridge if it is running 65-75% of the time.
I would be replacing it asap.

That's the design criteria for refrigerators. If you don't believe it, put a time clock chart on it. That figure may be on the low side.

GE Appliances wrote:
Refrigerator Normal Run Time

For refrigerators and freezers to maintain proper temperature, the compressor will run much of the time. Newer refrigerators have compressors that are designed to run 80% to 90% of the time. This makes them more energy efficient because the greatest amount of energy is used when the compressor cycles on as opposed to when the compressor is actually running.

https://products.geappliances.com/appliance/gea-support-search-content?contentId=16932

My 7 year old fridge at home runs maybe 30% of the time (15-20 mins out of an hour).

Every fridge comes with an energy guide sticker. A Haier 9.8-cu ft Top-Freezer uses 327 kWh of power per year. This translates to 895 Wh per day. This is about 37 AH per day.

Tom_M wrote:
Every fridge comes with an energy guide sticker. A Haier 9.8-cu ft Top-Freezer uses 327 kWh of power per year. This translates to 895 Wh per day. This is about 37 AH per day.

That's the fridge I'm installing. Will only be on inverter to cool down before leaving on a trip. We don't boondock, always have shore power. So I think my existing batteries can handle about 10 hours overnight to do cool down.

theoldwizard1 wrote:

2oldman wrote:
4 deep cycle, and solar.

Concur ! In my book, "deep cycle" means 6V golf cart batteries. 4 GC2 batteries (2 in series and those in parallel with the other 2 in series). That will give you OVER 400 Ah @ 12V.

6V AGM golf cart batteries are available (Trojan T105-AGM), but they are expensive. You would have to order them through a golf cart store or a solar power store.

Only be using batteries to cool down overnight before leaving in morning. No other power draw, inverter set up for fridge use only.

Romer1 wrote:
Will be replacing my dead Norcold N821 with a 9.8 cu ft residential in 2 weeks. Refrige draws 6.0amps/690 watts on start and 2.5amps/287.5 watts running. Planning on a 1200 watt PSW inverter which will handle load . Question is how much battery do I need?

Are you getting these numbers off the compressor or spec sheet? If so they are probably AC numbers. IIRC My compressor says .5 which is 5 amps DC. If it said 6.5 amps start up that would equate to 65 amps DC. I tried a magic chef from HD first and it wouldn’t start on a 1000 watt Xantrex. I then went to a 2000 watt Xantrex and I believe a whirlpool 10.8 cf from best buy. Its going on 4 years since i installed it so I’m remembering every number exactly right but Im thinking it was a daily amp hour use of about 75 AH.
Multiply any AC numbers by about 10 to get DC numbers
Im running 6 GC2 and 1000 watts of panels.

Edit:
Another thing that happens with inverters is that by the numbers it should work but thats also considering that you have enough battery and heavy enough cables. No matter the what the numbers say that start up spike can sometimes freak the inverter out. Just mentioning it so you can plan accordingly. Leave room for up sizing everything just incase your experiment varies. Also dont over estimate how long it can be off and keep things cold or frozen. I heard very optimistic comments on here yet had very different results the one time i tried it. Your results may be better

When my defrost kicks in it pulls 20 some amps DC for 10 minutes or so. Defrost probably comes on each day. I know that each time its powered off and back on it does a defrost cycle.

Our RV came with residential appliances, an 1800W inverter, and 4 golf cart (GC2) 6V batteries. The engine has it's own dedicated battery and is isolated with the key off.

I have solar power at home, and I've been using a Xantrex Prowatt SW2000 Inverter 24/7/365 for almost 8 years to power a portion of my home. The power is cleaner than grid power. Screen shot of my inverter's output:



Keep in mind this inverter needs to be fairly close to the battery bank, and fed with 4/0 cables. Power in, equals power out (minus losses). A 1000W load at 120V is 1000/120 = 8.3A But to do the same work with an inverter, using 1/10th the supplied voltage, takes 10 times the current.. 1000W load at 12V is 1000/12 = 83.3A This is why the cables need to be so large.

Here's what I'm feeding each of my inverters:



Here's the recommended cable size per Xantrex:



Refrigerators have a small compressor. That's not the issue. It's the defrost cycle that puts a large demand on the inverter and batteries. Worse yet, many fridges immediately go into the defrost cycle when power is first supplied.

Here's the data from the two house fridges at had at the time of testing:

Refrigerator in garage: Not running but on: 0 Watts. Compressor running: 114-140 Watts. Total per day: 1.15 KW, 47.92 Watts per hour average.

Refrigerator in house: Compressor running: 146 Watts. Defrost: 572 Watts. Total per day 2.15 KW, 89.58 Watts per hour average.

It just so happens that the RV came with the exact inverter I have at home. Consequently, it works flawlessly, just as the other one I'm using.

It's always good to have more inverter than you currently need. If you decide to put anything else on it, overloading will be less of an issue. Prices have also come down on these, so not a huge difference in price between power ratings.

You can see all the specs on Amazon: Xantrex PROWatt 2000 Inverter

Romer1 wrote:

theoldwizard1 wrote:

2oldman wrote:
4 deep cycle, and solar.

Concur ! In my book, "deep cycle" means 6V golf cart batteries. 4 GC2 batteries (2 in series and those in parallel with the other 2 in series). That will give you OVER 400 Ah @ 12V.

6V AGM golf cart batteries are available (Trojan T105-AGM), but they are expensive. You would have to order them through a golf cart store or a solar power store.

Only be using batteries to cool down overnight before leaving in morning. No other power draw, inverter set up for fridge use only.

Absolutely no reason what so ever to "cool down" a residential fridge over night.

It WILL be ready in ONE cooling cycle which from 60F-110F ambient air temp should not be much more than 40 minutes to one hour!

Throw all of your cold and frozen food in the fridge then start it up on inverter and get on the road.

We are not talking a RV absorption fridge which can take 12hrs to 24hrs..

Residential fridges rock with much faster recovery rates..