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12v Fridge-Daily run-time estimate in hrs??


ToyoGuy

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Howdy All,

I am doing calculations of amp-hours on all appliances to determine what size batteries to buy for a solar project and I have an EdgeStar FP 430 12v/120v fridge that draws about 5.4 amps @ 65 watts, as near as I can figure. What I don't know, is about how many hours per day, on average and in "clement weather" (like 60's to 70's in the coach) the thing will be running to keep stuff cool. Has anyone with a 12v fridge studied this "Duty Time" problem before and come up with a SWAG or better guess that has worked out? The fridge and the furnace fan are the high-ticket items, so far, but the fridge will be the real deal-breaker, if I get it wrong. Thanks for the benefit of any of your collective experiences.

BR,

TG

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From what I've seen at 70 degrees a "dorm" refer is around a 50% duty cycle. Adding an external insulation blanket or gluing some foam boards to the outside of the refer has a huge impact

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5.4 amps= about 65 watts I think you mean 12 volts. Is the fridge a modern 12 volt thing or a dorm fridge? The new stuff is very efficient and often chest type (like a cooler) they are the best. Dorm fridge on 12 volts is going to suckup power they are not real efficient and their start current is quite high add the heater and on a cool night you'll end up with dead batteries all the while you are keeping warm you are heating the fridge. For the price a efficient modern 12 volt fridge you are better off with a gas fridge you can store far more energy in a 20# propane tank then you can in 10 batteries. I love my gas fridge it would be repaired or replaced before I would consider anything else.

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Hey thanks guys.

Linda, you find more stuff online that I've never seen.....  Jeeze.

Thanks Maineah, mine is 12v like the one Linda included the link to the test for. Funny though, in the specs the guy shows on the side of the fridge, it shows 4.5 amps DC with 65 watts at 12 volts. They must be using the new math. With W = V x A,  at 12 volts, I get 5.4 amps like you.

The tester's claim is that once it's cooled down, to maintain approximately 35 degrees, at normal temperatures, the compressor runs about 10 mins per hour. That would be about 4 hrs per day, or 21 1/2 ah per day, I'm just not buying it.  I think WME is closer to the truth at 30%-50% duty cycle, depending on contents , coach temp and how often you raid the icebox.My calculations will put me at about 65 ah per day to allow for heat and running the furnace when it's frosty outside.

My fridge is mounted under a counter, on a pull-out shelf (below) and, while it's well vented with 3 vents, I think I'll install a small switchable computer-like fan to help vent the coils.

All in all, I'm hoping that once I get a couple of 6v deep-cell batteries installed in parallel, with 200 watts in panels and a good controller, I'll be OK. I already learned about using the furnace and the fridge concurrently the hard way. :clown2:

Thanks again,

TG

 

Multi Inter 1.jpg

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That would be two 6v batteries in series

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I installed a fridge in a friends Sprinter it's about the size of an original gas fridge it uses a "swing" compressor very efficient very expensive but they love it. They have get this, a 1000 amp battery it is a two person lift I installed a 65 amp charger and isolator system so far so good they have been everywhere with the Sprinter and have had no issues with the fridge. The chest type is the most efficient hands down just because cold air sinks too bad there is not enough room where the old fridge was to put it in there. 

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Right, WME, in series . There's a reason I use the clown emoticon more than anyone else on this forum.......  

Linda, thanks SO much for the link. That is exactly what I was looking for. Now I can copy some of those specs, and together with the rest of my notes, head to the battery store.

Maineah, I have heard about those swing-compressor rigs, after I bought mine, of course. I am pretty happy with the performance of mine, for the price. The only thing I would do different now is buy the model with side by side freezer and fridge that are independently controllable for about $60 more, but that was not available when I did my build. (It's about 1 1/4" wider, side to side and won't fit in my cabinets as constructed, darn)

One simple modification I have made for this fridge (below) that is SO worth the time and effort (in my humble opinion) is the fabrication of plastic shelves to separate the bottom area from the top and keep things cooler at the bottom and from getting crushed. I put meats and stuff on the bottom of the fridge and drop in the 1/8" plastic baffle, then I can stack stuff on top like lettuce and fruit etc.I do also use a little double-A battery powered fan with it, and It the difference from using the shelf is major. With the basket in the EdgeStar, you can set the plastic shelf/baffles to 2 heights. The holes for grabbing the shelves are about 1 1/2" and seem to promote just the right amount of circulation of air.  I also cut out a plate for the bottom of each side so things would "set" on them better, like ketchup or soda cans etc. Anyway, like they say,..."It worked for me".

Thanks again to you all,

TG

Top level.jpg

Side.jpg

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Thanks WME, that looks more omni-directional than mine. Wow, a year per battery change!

Also, for anyone else trying to figure their present NON-deep cycle RV/Marine battery's amp-hour capability ( How many amp-hours it will support the amp-load of a certain appliance or group of devices) .........

I present .........Interstate's amp-hour formula below. :sorcerer:

I used the formula on my fridge using 5.4 amps and it came out just about right at about 20 hours of usage from 84 amp-hours of storage in the coach battery. The battery in question is an Interstate Marine/RV SRM-24 with 550 Cold Cranking Amps and Reserve Capacity rating of 140. This is a battery advertised as deep-cycle, but is not actually. I'm impressed that it makes that many amp hrs actually!

Per Interstate's site:

"To calculate the estimated amp hour rating for your automotive or deep-cycle battery, take the reserve capacity rating and multiply it by 0.6 to get an approximate Ah rating.

The Ah rating describes the ability of the battery to provide power over a 20-hour period. If the rating is 100 Ah at the 20 hour rate, then the battery can supply 5 amps for 20 hours. (5x20=100)."

(Don't forget to consider amperage loss due to wire-size and length)

Anyway, If you're still with me, I hope this might help some confused jamook who's working through this stuff, like me.

BR,

TG

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