Fridge on battery or AC?

[Outsider]

Long story short, 2020 GeoPro 19FD with 2- 6v Golf Cart batteries. If I have no gas, which makes more efficient use of the batteries, running in DC mode or turning the on-board inverter ON and running on it? NOTHING else will be turned on at all. I will be traveling during this time and getting some charge from a roof mounted 100 W solar panel.

Thanks for your help.

[lazyjj]

If only concerned while traveling, depending on the amount of hours you are on the road, you should be fine. We have only one 12V battery in our coach with a 50 Watt solar panel. Our refrigerator is the 12V Compressor model. We make a 8 to 9 hour run and everything stays cold and frozen in our refrigerator. Your tow vehicle is more than likely assisting somewhat in keeping the batteries charged.

[Chuck_S]

The missing information here makes this a WAG -- wild *** guess. How much power does the refrigerator draw? If running thru an inverter what's the inverter draw? Total draw?

Once we get that information (and it's all on the data plates) we can make this a SWAG -- sophisticated WAG. Preliminary WAG: Prime mover (truck) alternator should furnish sufficient power when the engine is running and not depend on batteries.

Both my wife and daughter go into a trance in front of an open refrigerator door -- avoid that on minimal power sources.

-- Chuck

[PhilFromMaine]

Originally Posted by Outsider

Long story short, 2020 GeoPro 19FD with 2- 6v Golf Cart batteries. If I have no gas, which makes more efficient use of the batteries, running in DC mode or turning the on-board inverter ON and running on it? NOTHING else will be turned on at all. I will be traveling during this time and getting some charge from a roof mounted 100 W solar panel.

Thanks for your help.

Inverters use between 3-8 percent more watts just to operate.

[Ballistic]

If you're traveling (motoring down the road) either method will work as it's all powered by the alternator at that point. From an efficiency perspective, it's always best to power devices by its native power. There are never efficiency gains when power is inverted/converted, only losses.

[Aussieguy]

best that you read up on how your particular fridge works power sources , how level and how does outside temperature effect it's performance.


In GENERAL terms :
Propane is better at cooling but you need to replace the gas used.
Lots of people use it even when driving down the road it is safe.


Don't over tax it, by filling it with a lot of room temperature stuff and then trying to cool it all down at once.
-----------------------------------------------------------------

If you want more efficiency on 12v
consider swapping out your fridge for a compressor model....
better capacity and keeps things cold real well.


OR purchase a portable 12v freezer or fridge to increase your capacity
place it in the tow vehicle.

[boondocking]

According to the spec for that trailer it has a 12v fridge. So battery power only when traveling.

[NavyLCDR]

Originally Posted by Outsider

Long story short, 2020 GeoPro 19FD with 2- 6v Golf Cart batteries. If I have no gas, which makes more efficient use of the batteries, running in DC mode or turning the on-board inverter ON and running on it?

Direct DC will always be more efficient than providing power through an inverter.

[bikendan]

Originally Posted by boondocking

According to the spec for that trailer it has a 12v fridge. So battery power only when traveling.

It would have helped if the OP had posted the make and model number of their fridge.

[Outsider]

OP here - a couple of clarifications: 1) As stated, this is a 2020 GeoPro 19FD and it has the factory installed 3-way fridge (gas, AC, DC) which I love. I normally pre-cool the food and the fridge (on AC as I did this time) but I found out Thursday morning 10 minutes before leaving on a 1-way 1400 mile trip that the gas valve was not tripping to allow it to light. That is the reason for the question. I had never run the fridge on TT battery DC and was looking for the most efficient choice. We will have 4 nights on the road with temps about 35-40 degrees each night and I didn't want to run out of battery for either the food nor for knocking the chill off the TT with the gas furnace when we get up each morning. So it sounds like the consensus is that straight TT batter DC is probably the better choice choice - right?


(Don't step away from the intent of this conversation but as a side note, I'm a pretty good mechanic with lots of common horse sense and proved that the gas line valve was never getting the needed voltage to open and allow gas to flow and then light. I'm also a very dedicated Christian and believe in the power of a loving God and Heavenly Father who I walk with in all things that I do. After stopping to turn the matter over to Him in prayer and trusting in His best for me for this trip I tested the fridge one final time and "click", the valve opened up and it lit. So my problem is solved but I'm still attempting to gain wisdom and knowledge from this experience.)

[boondocking]

Good to hear that it is a 3 way fridge, gives more options.

The Forestriver website says it is a 12v fridge (Kitchen Features). They should correct that mis-information.

[bikendan]

Originally Posted by boondocking

Good to hear that it is a 3 way fridge, gives more options.



The Forestriver website says it is a 12v fridge (Kitchen Features). They should correct that mis-information.

That information is for the 2023 version, he has a 2020 version, before 12v only fridges became the rage.

[Ballistic]

Edited

[BehindBars]

Originally Posted by Outsider

OP here - a couple of clarifications: 1) As stated, this is a 2020 GeoPro 19FD and it has the factory installed 3-way fridge (gas, AC, DC) which I love. I normally pre-cool the food and the fridge (on AC as I did this time) but I found out Thursday morning 10 minutes before leaving on a 1-way 1400 mile trip that the gas valve was not tripping to allow it to light. That is the reason for the question. I had never run the fridge on TT battery DC and was looking for the most efficient choice. We will have 4 nights on the road with temps about 35-40 degrees each night and I didn't want to run out of battery for either the food nor for knocking the chill off the TT with the gas furnace when we get up each morning. So it sounds like the consensus is that straight TT batter DC is probably the better choice choice - right?


(Don't step away from the intent of this conversation but as a side note, I'm a pretty good mechanic with lots of common horse sense and proved that the gas line valve was never getting the needed voltage to open and allow gas to flow and then light. I'm also a very dedicated Christian and believe in the power of a loving God and Heavenly Father who I walk with in all things that I do. After stopping to turn the matter over to Him in prayer and trusting in His best for me for this trip I tested the fridge one final time and "click", the valve opened up and it lit. So my problem is solved but I'm still attempting to gain wisdom and knowledge from this experience.)

This thread seemed like a good discussion about the refrigerator and it’s energy sources, but I now feel it has “jumped the shark”. If talking to the deity fixed the gas valve problem, why not ask it the battery vs AC question, too?

[boondocking]

Originally Posted by bikendan

That information is for the 2023 version, he has a 2020 version, before 12v only fridges became the rage.

That makes sense, thanks.

[pgandw]

Originally Posted by Outsider

OP here - a couple of clarifications: 1) As stated, this is a 2020 GeoPro 19FD and it has the factory installed 3-way fridge (gas, AC, DC) which I love. I normally pre-cool the food and the fridge (on AC as I did this time) but I found out Thursday morning 10 minutes before leaving on a 1-way 1400 mile trip that the gas valve was not tripping to allow it to light. That is the reason for the question. I had never run the fridge on TT battery DC and was looking for the most efficient choice. We will have 4 nights on the road with temps about 35-40 degrees each night and I didn't want to run out of battery for either the food nor for knocking the chill off the TT with the gas furnace when we get up each morning. So it sounds like the consensus is that straight TT batter DC is probably the better choice choice - right?

(Don't step away from the intent of this conversation but as a side note, I'm a pretty good mechanic with lots of common horse sense and proved that the gas line valve was never getting the needed voltage to open and allow gas to flow and then light. I'm also a very dedicated Christian and believe in the power of a loving God and Heavenly Father who I walk with in all things that I do. After stopping to turn the matter over to Him in prayer and trusting in His best for me for this trip I tested the fridge one final time and "click", the valve opened up and it lit. So my problem is solved but I'm still attempting to gain wisdom and knowledge from this experience.)

The manual start 3 way fridges I have used in pop-ups and A-frames have some sort of temp regulation on AC and propane, but none on DC. The simpler models were essentially a standard SCR dimmer (same as dimmer for household lights) for AC, and an adjustable valve for propane. DC mode was just turning on the DC switch, making sure the AC and propane were off. A caution - the DC mode on Dometic RM 4223 took about 10 amps.

My tow vehicle at that time would only supply 10 amps before voltage at the trailer would droop to 12.9V. No effective battery charge at that voltage when fridge was on DC. The fridge would not stay lit on propane in side wind conditions at 55+ MPH and did not have auto-start, so had to tow on DC. Any stop where I left the fridge running on DC would deplete some of the battery charge, and would not replenish if fridge was running.

My latest A-frame fridge (Dometic RM 2354) has an inside control panel, and can/will auto-start on propane, so I tow on propane (actually I just leave in "Auto"). According to the operating manual, the thermostat operates in DC mode. If there is thermostatic control in DC mode, the DC mode should be slightly more efficient running off battery than in AC mode going through an inverter.

However, coil sizes matter in warm weather. The DC coil is often smaller (in watts) than the AC coil, and would therefore have less maximum cooling capacity (on full time on coolest thermostat setting). Check the spec plates for the wattage of the 2 coils.

So in good lawyer-speak, "it depends". Specs for your specific fridge matter. Dometic fridge manuals can be downloaded from the Dometic site. And there are manuals available here at FRF.

Fred W
now 2019 Flagstaff T21TBHW A-frame with Dometic RM-2354 fridge
then 2014 Rockwood A122 A-frame with Dometic RM-4223 fridge
prev 2000 Coleman PUP with unknown fridge