Isotherm AC / DC Refrigerators and Freezers

[Sum Escape]

I assume these are "native" DC with the AC power coming through an inverter "brick" or similar? And that they look for AC first if both are available. Are these assumptions correct?
So a question is this. If away from shore power, not running genset and the refrigeration running on AC from an inverter bank of batteries, I assume they would be more efficient by turning off the AC source at the breaker panel and running them from the DC breaker skipping the inefficiency of the inversion. Correct assumption?

 

[Mark Searay]

Following

 

[sbw1]

Our Tiara had a 12 volt Isotherm that was wired to the DC circuit. No AC at all. Great fridge.

 

[bbwhitejr]

I believe you are correct. It looks for 110v and if not available it switches to 12v. I just got an Isotherm freezer running. After 24 hours, it was down to 0.9* and was set on 5 out of 7. Am planning to buy an Isotherm refrigerator to put in the cockpit very soon. I think I am really going to like the separate refrigerator/freezer. I bought a brand new Norcold 14 months ago. If the freezer went below 16*, everything in the refrigerator would freeze....

Bennett

 

[Charlesoceanone]

I believe you are correct. It looks for 110v and if not available it switches to 12v. I just got an Isotherm freezer running. After 24 hours, it was down to 0.9* and was set on 5 out of 7. Am planning to buy an Isotherm refrigerator to put in the cockpit very soon. I think I am really going to like the separate refrigerator/freezer. I bought a brand new Norcold 14 months ago. If the freezer went below 16*, everything in the refrigerator would freeze....

Bennett

The Po took out the washer dryer and replaced it with a refrigerator freezer in the hold under galley stairs. We love it.

 

[Jeremygavin]

It is correct that they are DC powered and use a transformer to get the AC to DC. They look for AC first and then run on DC of non is found. It would seem to me that it would be better to run it on DC instead of an inverter. If you are taking DC power converting it to AC power at the inverter and then converting it back to DC at the fridge, I would be certain that there are some power losses on those conversions. They are set up to run on DC as is, why change it. I can run the boat all day on battery and have no issues. I have converted all lights to LED so that helps. Also, if your fridges are running off the house battery then that will save your inverter battery for other uses.

 

[Sum Escape]

It is correct that they are DC powered and use a transformer to get the AC to DC. They look for AC first and then run on DC of non is found. It would seem to me that it would be better to run it on DC instead of an inverter. If you are taking DC power converting it to AC power at the inverter and then converting it back to DC at the fridge, I would be certain that there are some power losses on those conversions. They are set up to run on DC as is, why change it. I can run the boat all day on battery and have no issues. I have converted all lights to LED so that helps. Also, if your fridges are running off the house battery then that will save your inverter battery for other uses.

Thanks Jeremy, you confirm my thinking.

 

[rlynch03]

Thanks Jeremy, you confirm my thinking.

I have also wondered which is the lesser evil.
1) Have the fridge/freezer run slightly inefficient but is powered via 120v shore power or generator power.
2) Run the fridge/freezer from the house bank of batteries at 12v (so no conversion on the units required) but that requires your battery charger to continually switch from float to charge and keep the batteries topped off.

Seems to be inefficiencies either way.

 

[Sum Escape]

I have also wondered which is the lesser evil.
1) Have the fridge/freezer run slightly inefficient but is powered via 120v shore power or generator power.
2) Run the fridge/freezer from the house bank of batteries at 12v (so no conversion on the units required) but that requires your battery charger to continually switch from float to charge and keep the batteries topped off.

Seems to be inefficiencies either way.

My original question was if no AC from shore or genset, would DC be better. I think we have confirmed this.
If running genset or on shore power, I think leave refrigeration on AC is better.
But these are my opinions, YMMV.

 

[ttmott]

Converting AC to DC such as powering DC devices or charging batteries there are electrical losses to heat as well as similar losses in inverting DC to AC. The advantage to AC is there are virtually no voltage drop issues over line lengths compared to DC. I think you will find, for the most part, that the bulk of the electronics on the refer are operating regardless so AC/DC current draw differences would pretty much be in the noise. So, if you are drawing off the batteries and charger/converter or powering from the AC system I would doubt anything significant would be different. Now, obviously running the generator just to operate the refer is nonsense; use the batteries and then use the generator when the batteries need charging.... Conversely, if the generator is running anyway then I think it best to operate the refer on the generator.