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Old 20-07-2016, 10:00   #1
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Refigeration Amp Hour usage survey

Hi Everyone.

Thought I would put it out there , how many Amp Hours is your 12v DC refrigeration using in any given day (24hrs) on average ?

You can include size of fridge , ambient temperatures, amount and kind of insulation , make of equipment , and what ever else you can think of, if you like .

But Amp Hour usage is the main point.

I will start . I use 28 amp hrs on average.

Ambient temps are 87 during the day and 70 at night

Box is 7.7 square feet ,
5 inches of Polyisocyanurate insulation and 1 inch of polystyrene (blueboard)

Built my own condensing unit using a Danfoss BD35 using thermostatic expansion valve with a rollbond evaporator plate 16" x 32" in size .

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Old 20-07-2016, 10:16   #2
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Re: Refigeration Amp Hour usage survey

Mine is about 100+ AH, Factory old ice box, Cool Blue custom unit with BD-80 compressor and dual cold plates, 14 cu ft with about 7 being freezer, spill over.
Temps mid to high 90's in the day and high 70's to low 80's at night
Box temps are close to 0 in freezer and about 40 in fridge side. 30 yr old inadequate insulation is I'm sure why consumption is so high, but the system handles it anyway.

I think most systems if decently designed will be about equally efficient, it's things like how often box is opened, front or top opening, amount and quality of insulation, box temp that will be your wild cards, especially insulation
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Old 20-07-2016, 10:45   #3
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Re: Refigeration Amp Hour usage survey

Quote:
Originally Posted by a64pilot View Post

I think most systems if decently designed will be about equally efficient, it's things like how often box is opened, front or top opening, amount and quality of insulation, box temp that will be your wild cards, especially insulation
Very true. We have a 30 year old A/B runs 60 ah per day: 5A when running, 50% cycle when the box is filled and cooled off.

Record of Daily Energy Use of 100 ah per day:

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Old 20-07-2016, 10:57   #4
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Re: Refigeration Amp Hour usage survey

Hey Pilot

That's a big box you are cooling , and a deep freeze as well !

I agree , each system will be around the same efficiency if designed right .

I keep my fridge between 2 and 4 degrees Celsius. And don't open it more then I have to .

I have yet to do my freezer which has its own cabinet . I figure around a 3 cubic foot box with the same set up for a condensing unit . That should add to my amp hour usage .

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Old 20-07-2016, 11:02   #5
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Re: Refigeration Amp Hour usage survey

I have a large freezer with an even larger frig cooled by a spillover system with a fan between the two (don't know the dimensions). Based on 3 years of solar controller daily data that on average puts 60AH/day into the batteries with no one on the boat I feel my system uses around 45-50AH/day.
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Old 20-07-2016, 11:17   #6
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Re: Refigeration Amp Hour usage survey

It's almost too big, and too deep.
My plan is to eventually add insulation to the the inside of it and especially the floor and hopefully we won't need the stool to reach the bottom anymore, and cut down on energy consumption. It was an ice box, and I think the idea was you could put several days worth of ice in there, that would raise the bottom and still leave plenty of room for food.
I've been toying with getting an Engle or similar and using it as a freezer for when we are gone for months, but will likely wait and see if that is really needed or not.
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Old 20-07-2016, 12:10   #7
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Re: Refigeration Amp Hour usage survey

Just for comparison, my cheap 120V fridge and inverter ($200), only 3.5 CF but has a small freezer, runs 60 ah a day. It's now 9 years old and still going strong.

Mind you it pulls 15 amps when running, but duty cycle is about 16%.
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Old 20-07-2016, 12:16   #8
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Re: Refigeration Amp Hour usage survey

My fridge is 27 inches deep from the counter top.
Seems to work just fine , wife is happy , she can reach the bottom .

You can just see the bottom .
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Old 20-07-2016, 12:36   #9
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Re: Refigeration Amp Hour usage survey

Fridge just shy of 8 cubic ft. Aerogel insulation, 3" on sides and top and 4" on bottom. Temps are 100 degrees during day and 90 at night. It's a Danfoss 50 compressor average use is 6+ amps when running. Average 24 hour amp hours is 30.
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Old 20-07-2016, 12:57   #10
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Re: Refigeration Amp Hour usage survey

About a 10-12 cu ft freezer and a spillover bar sized fridge about 70 amps per day in the Bahamas (temp usually in the eighties). AB cold machine .
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Old 20-07-2016, 12:58   #11
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Re: Refigeration Amp Hour usage survey

I have thought to add an hour meter to get a better feel for the run hours
On a BD50, can I get the time from the thermostat? I know the BD senses the amp load from the fan so cannot get it that way.
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Old 20-07-2016, 13:02   #12
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Refigeration Amp Hour usage survey

I think you can get it from the fan, and I think there my be an unused plug on the controller that can be used to power an additional fan, so you should be able to get it that way too.
Not sure but I think the thermostat just completes a circuit, so I don't think you can run an hour meter off of it.
Hour meter ought to pull almost nothing, I doubt it would look like a fan over amp


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Old 20-07-2016, 13:06   #13
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Re: Refigeration Amp Hour usage survey

0... engine drive...
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Old 20-07-2016, 13:43   #14
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Re: Refigeration Amp Hour usage survey

[Q UOTE=sailorchic34;2170775]Just for comparison, my cheap 120V fridge and inverter ($200), only 3.5 CF but has a small freezer, runs 60 ah a day. It's now 9 years old and still going strong.

Mind you it pulls 15 amps when running, but duty cycle is about 16%.[/QUOTE]

Your 120 v fridge runs only 16% of the time? light years ahead of anything I've ever owned. What brand is it and what Is the climate where you are
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Old 20-07-2016, 14:35   #15
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Re: Refigeration Amp Hour usage survey

We have an isotherm unit in our fridge installed by me. The box is standard built in by the boatbuilder so is now 28 years old. The fridge draws about 7A when it runs and the fridge has a duty cycle of about 42% (runs 16 min, off for 22 min). Average ambient is about 21 degrees in summer and about 14 in winter. So I figure my summer consumption per 24 hours is around 72Ah.

My wife is vertically challenged and the depth of the top-loading box meant that she could never reach the bottom. In addition, there was a removable shelf halfway down which meant that the top half of the fridge needed to be unpacked to get to the bottom half, a most inefficient and undesirable condition.

So I figured that temp retention couldn't get much worse so I cut a big hole in the front bulkhead and fabricated a system of two SS drawers to go in. Now we have easy access to the bottom of the fridge. I insulated the fronts of the drawers as best I could and expected the duty cycle to go to hell. But it didn't change much - I think the fact that we no longer need to unpack the fridge has equaled the loss in thermal efficiency of the drawer fronts. BTW, the insulation in the front wall was 3.5" urethane foam so I'm guessing it's the same on all walls.

So our fridge layout now is fresh produce and meat in the top, a small drawer for "smalls" (cheese, cold meats, butter, etc.) and a larger drawer at the bottom for drinks. It is a brilliant layout for us because my wife can now easily get me a cold beer

Our freezer is an antique 110v unit with eutectic plates run through the inverter - it sucks about 80A when it runs. It doesn't see a lot of use . We'll replace it with an Isotherm unit sometime in the future.
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