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Old 26-03-2024, 07:42   #1
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Fridge 12v vs AC?

Hi all.

My new fridge can be powered with AC or DC
I am off the grid
I to save any power I can

which is best AC or DC connection for the fridge

Thx all!!
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Old 26-03-2024, 12:23   #2
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Re: Fridge 12v vs AC

Quote:
Originally Posted by Xavierp View Post
Hi all.

My new fridge can be powered with AC or DC
I am off the grid
I to save any power I can

which is best AC or DC connection for the fridge

Thx all!!
What kind battery and how many AH you have, what brand and wattages is your inverter and how many watts the fridge uses in 12 and in 110 or 230V?
Inverter running 24/7 anyhow eg because starlink? If that answer is no go for DC as alone the draw of inverter itself is significant.
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Old 26-03-2024, 12:24   #3
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Re: Fridge 12v vs AC?

Efficiency wise, there's no inherent reason why a DC vs AC fridge matters if you're already running an inverter 24/7 for other reasons. It's down to the efficiency of the specific fridge you install.
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Old 26-03-2024, 13:26   #4
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Re: Fridge 12v vs AC?

I could go either way. There will be efficiency loss with the inverter, which would favor a DC unit. Less an issue if the inverter is on anyway. However, the DC units efficiency is affected by battery voltage. So if you have too much voltage drop in wires to the unit, AC might gain an advantage. LFP would be much preferred over LA for this reason.

I have met a few sailors that get more battery life running the inverter and their fridge in A/C mode, than running the same fridge in DC mode. But in general, I think the opposite is true, that DC would be more efficient.

But really, if you want a fridge that is efficient, it is ALL about the insulation. Having had a couple brands of already built fridges, they don't hold a candle to a custom built and well insulated unit.
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Old 29-03-2024, 18:22   #5
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Re: Fridge 12v vs AC?

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Originally Posted by wholybee View Post
I could go either way. There will be efficiency loss with the inverter, which would favor a DC unit. Less an issue if the inverter is on anyway. However, the DC units efficiency is affected by battery voltage. So if you have too much voltage drop in wires to the unit, AC might gain an advantage. LFP would be much preferred over LA for this reason.

I have met a few sailors that get more battery life running the inverter and their fridge in A/C mode, than running the same fridge in DC mode. But in general, I think the opposite is true, that DC would be more efficient.

But really, if you want a fridge that is efficient, it is ALL about the insulation. Having had a couple brands of already built fridges, they don't hold a candle to a custom built and well insulated unit.

all true...in case of voltage drop, especially in 12V i highly recomment to use 12/12/30A Victron isolated Tr-orion which creates from 9-17V a stabilzed adjustable output. that i installed right at the main power input of the switchboard and output voltage at 14,8V compensates voltage drop&stabilze the power so the compressor of fridges/freezer as well as sweet water pump have minimum stable 13.6V at the input terminal. like this they run much better with much less losses...yes the stabilzing&upscaling costs energy but the losses are much smaller and eg waterpump runs shorter and keeps pressure much better. also good for livespan of pumps/compressor and if you have electric toilets..short all with a motor.
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Old 02-04-2024, 09:31   #6
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Re: Fridge 12v vs AC?

I spoke with the Whynter, the company that makes the freezer/fridge.
They gave me very detailed info which results in showing:

AC - 1.07 Kwh / 24h = 10 Ah
DC = 65.6 Ah

Is it even possible?

Attached is their specs sheet.
Attached Files
File Type: pdf FM-901DZ-Comsumption-Chart-1.pdf (397.6 KB, 22 views)
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Old 02-04-2024, 11:21   #7
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Re: Fridge 12v vs AC?

Quote:
Originally Posted by Xavierp View Post
I spoke with the Whynter, the company that makes the freezer/fridge.
They gave me very detailed info which results in showing:

AC - 1.07 Kwh / 24h = 10 Ah
DC = 65.6 Ah

Is it even possible?

Attached is their specs sheet.
No, that does not make sense at all, and it does not match the spec sheet attached. The spec sheet is a bit odd because it gives consumption as kWh for AC power, and Ah for DC power. Converting the units and using 90F ambient at -0.4F freezer:

AC = 1.01kWh
DC = 0.747kWh

And converting to Ah run by a 12V battery:

AC = 84Ah
DC = 62.3Ah

The error in your number might be incorrectly converting the 1.07kWh to Ah. If you are counting Ah in a 12V battery (running and inverter) you need to divide by 12) it appears that 1.07 was divided by 110.
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Old 02-04-2024, 18:04   #8
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Re: Fridge 12v vs AC?

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Originally Posted by rslifkin View Post
Efficiency wise, there's no inherent reason why a DC vs AC fridge matters if you're already running an inverter 24/7 for other reasons. It's down to the efficiency of the specific fridge you install.

Yep - Found that with my freezer - A lot of new 240V Freezers are now highly efficient - I got the most efficient one that I could find that fitted and the Amp draw, even with inverter was less than my previous 12V Freezer and for a bonus a 1/4 of the price!
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Old 12-04-2024, 04:56   #9
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Re: Fridge 12v vs AC?

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Originally Posted by UFO View Post
Yep - Found that with my freezer - A lot of new 240V Freezers are now highly efficient - I got the most efficient one that I could find that fitted and the Amp draw, even with inverter was less than my previous 12V Freezer and for a bonus a 1/4 of the price!
They all use evaporator plates, compressors and condensers. It is possible to mismatch them and lose some efficiency but you can't argue with the Carnot cycle. Most likely the isulation was poor in your old fridge or the compressors was worn, the gas weight was wrong. The inverter will have an inefficiency that a dc compressor fridge simply doesn't have
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