Fridge 12v vs AC?

[Wandering1]

Originally Posted by ranger58sb

I don't, but the Energy Star ratings people might. I've not ever noticed an Energy Star rating for an AC/DC "marine" fridge, but I haven't really been looking... and they might be out there somewhere.

Whereas an ES rating for household AC fridges are common as dirt... although the cost of inverter usage would have to be added, assuming periods away from shorepower.

If a particular unit is absent an Energy Star rating, I'd guess less efficient.

A point we've come to appreciate with AC units is self-defrosting, and a built-in icemaker in the freezer. That introduces some oranges amongst the apples, but...

-Chris

I guess to some extent it depends a lot on the boat. If you have a boat large enough to take a domestic AC fridge, you have the option. You probably have a lot more space for batteries and solar to charge so power is less of an issue.
Our main fridge is built into the boat and is only 100 litre capacity. The 10 litre freezer is in this fridge. The insulation is rigid board. 6" on the bottom, 4" on the sides and top. The Danfoss 45w compressor runs only 20 mins in the hour. We have a second portable compressor fridge that is our warm fridge. This is for fruit and veg. It's not as cool as the main fridge as veg doesn't need to be cold. It uses about the same power as the built in fridge as the insulation is not so good, even though we made and fitted and insulated jacket.
The power consumption of our fridges is not significant compared to the power we use to make water every day, cook on the induction hob and run the immersion heater. We do all this with 920w of solar and lithium batteries.
We have a seperate ice machine

[CaptainRivet]

If you can fit an A++ 230V freezer onto your vessel and run it via a Victron Phönix 500 or 800VA inverter that’s very very hard to beat, in energy consumption and a marine specific unit that will come close will cost you min 3 times.
That’s where the domestic units really shine. Fridge it’s similar especially costs but not that much on energy consumption side.

[newhaul]

Originally Posted by Xavierp

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!!

Hook up both as dual power fridges automatically switch when ac power is available if you have the ac side plugged into an outlet. However a 12v unit is most efficient power wise when running on dc. Then there are no converter or inverter power losses to heat.

[RaymondR]

Originally Posted by Statistical

Curious. That does sound like it could be a BLDC motor. My refrigerator compressor is (knock on wood) over 20 years old at this point so maybe they have improved things.

Side note yes the question of is BLDC "alternating" is one with no good answer. It isn't AC like we usually think of AC but it certainly does alternate.

Ozepete from Ozefridge sent me the diagram with an explanation of the progress made from the original Danfoss compressors and it appears that they are true three phase AC induction motors now.

[CaptainRivet]

Originally Posted by RaymondR

Ozepete from Ozefridge sent me the diagram with an explanation of the progress made from the original Danfoss compressors and it appears that they are true three phase AC induction motors now.

And thats why running these 3 phase AC compressor via the inverter on AC can cause such a massive difference in less consumption compared to DC as the fridge is not doing the job of making AC from DC and a good inverter like victron is much more efficent in that.

[rslifkin]

Originally Posted by CaptainRivet

And thats why running these 3 phase AC compressor via the inverter on AC can cause such a massive difference in less consumption compared to DC as the fridge is not doing the job of making AC from DC and a good inverter like victron is much more efficent in that.

From what I've seen, the Danfoss units don't have a big difference in power draw on AC vs DC. They can't just use the incoming single phase AC, they have to rectify it to DC and then drive their internal inverter to produce the lower voltage 3 phase output (which is also likely variable frequency to get different compressor speeds). The input power source doesn't change what the control box has to do to power the compressor.

[CaptainRivet]

Originally Posted by rslifkin

From what I've seen, the Danfoss units don't have a big difference in power draw on AC vs DC. They can't just use the incoming single phase AC, they have to rectify it to DC and then drive their internal inverter to produce the lower voltage 3 phase output (which is also likely variable frequency to get different compressor speeds). The input power source doesn't change what the control box has to do to power the compressor.

Yes because danfoss are from ground up optimsed for RV and marine DC use while other are not as used in a much wider range eg the LG compressors are known for running much better on AC then DC. It all comes down to design and construction and thats why you have to look at the datasheets they give you.
LGs are better then Danfoss and cheaper but need AC, they run on DC but conversion is better done by inverter...
Have 2 drawer fridges 20l, same size and one LG cost 450Euro and other danfoss cost 780Euro. Lg beats danfoss when running on AC plus quiter, danfoss beats LG on DC by far but total AH the LG on AC wins with a victron 800W phönix inverter i also have for the freezer.
LG has also more power in same size, going to -8 degrees celcius while danfoss manages 0 degrees and beeing the lower of the two stacked means its top is covered by the LG on top giving it a better isolation.

[RaymondR]

Originally Posted by CaptainRivet

And thats why running these 3 phase AC compressor via the inverter on AC can cause such a massive difference in less consumption compared to DC as the fridge is not doing the job of making AC from DC and a good inverter like victron is much more efficent in that.

I suspect it would be difficult to achieve greater efficiency than the small induction motors in the latest DC compressors. The MOSFETS on each phase are just reversing the current direction and I suspect the integration to a sinusoidal waveform is done by the induction coil each phase in the motor rather than by the drive electronics.

[newhaul]

Originally Posted by RaymondR

I suspect it would be difficult to achieve greater efficiency than the small induction motors in the latest DC compressors. The MOSFETS on each phase are just reversing the current direction and I suspect the integration to a sinusoidal waveform is done by the induction coil each phase in the motor rather than by the drive electronics.

Agreed you can't beat the efficiency of the new cubigel compressors .

[Wandering1]

Originally Posted by RaymondR

I suspect it would be difficult to achieve greater efficiency than the small induction motors in the latest DC compressors. The MOSFETS on each phase are just reversing the current direction and I suspect the integration to a sinusoidal waveform is done by the induction coil each phase in the motor rather than by the drive electronics.

I agree. Especially if you don't run an inverter 24/7. In this case you need to buy a fridge inverter. The best efficiency you can expect with something like a Victron phoenix would be 90% whilst the fridge is running. You then have a small continues inverter load whilst the fridge is off. None of this does much for overall fridge efficiency and you have the additional cost of buying a dedicated inverter.
Our DC fridge is so efficient it's a load we don't even think about.
Nothing like cooking loads, watermaker or hot water