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Doing the refregerator math

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TexasBorderDude
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Doing the refregerator math

Post by TexasBorderDude »

In looking at the energy ratings of a new fridge, it uses 555kwh per year on the energy guide comparison... that's roughly 1.6kw per day on 365 days. So what's the battery bank capacity required to run on an inverter? I'm figuring 70% efficiency on the volts/amps converted (inverted from 12 to 110 volts)... but can't get to the storage amps required to be consumed from the battery bank (I assume the fridge would only run 1/2 of the total time)

Thanks,

dg
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beltguy
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Re: Doing the refregerator math

Post by beltguy »

Doyle, I am not an expert on this subject, but no one has jumped in, so I thought I would give you a couple of thoughts.

Trying to size a battery bank from refrigerator manufacturers data can be a bit frustrating, since there are lots of variables. I looked at my fridge and the rating tag is long gone. It was rated well for it's type and the time (about 5 years ago). It is a side by side with water dispenser, so not as efficient as some.

The interesting approach my fridge uses to be "efficient" is a small compressor that runs longer. It drive me crazy to hear it running so much, but that is the nature of beast. When it is running, I can't see the draw on my 120V ammeter. I do look at my rather accurate Trimetric battery meter and I think it draws about 20 - 30 amps on 12V. It is hard to isolate the fridge current, since we have a bunch of electronic equipment running most of the time.

While my compressor is supposedly small, it has a pretty good surge that really dims the lights for a second or two. I was very worried that this surge load would damage my inverter long term, but after 3 years of 100% on time it just plugs along. It does, however, point out the need for a good inverter (should be full sine wave) that has good surge rating.

Speaking of inverters, a modified sine wave inverter will not provide full heating on microwaves, so you need to run it longer (more battery bank). I mention this because the inverter characteristics have a significant impact of battery bank capacity requirement.

Since you seem to be working on sizing the battery bank, let me make an observation. We have 8 golf cart batteries. I work very hard not to let them get below 50% of state of charge (as measured by the Trimetric). With reasonably conservative use of lighting, my batteries will only give me about 1/2 - 3/4 day of usage. The fridge is a significant draw, but there are lots of other consumers. The inverter itself has some current draw. As I mentioned, we have a lot of electronic stuff running (DVR, TV, Motosat/internet modem, up to 4 laptops, printer, etc) running at any given time. Then there are the normal kitchen appliances. The coffee maker can use about 5 amps AC and the microwave is at least 10 amps as I recall.

So, the fridge is probably less than 30 - 40% of our load.

One of the things that folks preach is to disable the defrost function. Most fridges use a heat strip in the door and that can consume a fair amount of power. Some of us have played with this, but modern fridges are "computer" controlled and trying to disable the heat stip can cause control problems. I finally gave up and just live with the problem.

Not sure any of this rambling helps, but at least you got a reply :D

Jim
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'85 Eagle 10 with Series 60 & Eaton AutoShift 10 speed transmission SOLD
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luvrbus
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Re: Doing the refregerator math

Post by luvrbus »

Doyle, forget about a house type fridge when we get back to AZ we will go to Prescott and look at the Millers propane( Amish made) and the SunFrost 12v or 24 volt fridges they will work best for you I think good luck

Clifford
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TexasBorderDude
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Re: Doing the refregerator math

Post by TexasBorderDude »

Ahhhhh Clifford! You are the best ever!!!! Hadda great birthday party with the grand daughter... see you in a couple of days.

Best,

dg
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