12 Volt Fridge freezer

[camperAL]

Just thought I would throw this out. When my wife and I have boondocked in Oregon or KOFA or both, we have went for three weeks with two
120 amp 6 volt batteries (wired to 12 volts) powering our fridge, furnace and powered our TV/DVD for 2 to 4 hours in a 24 hour period.

We were running our generator between two to four hours each day to charge things up. We keep an eye out for cooler temps so as not to underestimate our need for heat at night which is also relying on battery power as well. LP is our friend for fridge & heat.

That is probably 32 to 34 gallons of gasoline for three weeks or about 11 gallons per week. $50 plus per week at Quartzsite. A good trade off for 7 days. We really like this set up and ability to stay out and away from things on trips.

 

[Gary RV_Wizard]

As Lou says, modern compressor fridges are highly energy efficient. The only drawback from an RV perspective is that a battery doesn't stored anywhere near as much energy as a propane bottle, so you run out of electric "fuel" sooner than propane. It's the fuel tank size/capacity that makes the difference. A 20# propane tank is physically about the same size as 2.5 12v batteries, whether lead-acid or lithium.

 

[DonTom]

Actually compressor based refrigeration is significantly more efficient than absorption cycle refrigeration, using about 1/10th as much energy per BTU of cooling.

I really cannot say I know, but I have a difficult time buying that.

Besides the obvious fact that when boondocked the propane level doesn't drop a noticeable amount after a few days and nights of only running the refrigerator. But I think most would notice that 8-amp draw or whatever on their house batteries. But I also realize that 8-amps is not 100% of the time, just when the compressor is running. But on a warm day, what would that duty cycle be?

-Don- Reno, NV

 

[DonTom]

As Lou says, modern compressor fridges are highly energy efficient. The only drawback from an RV perspective is that a battery doesn't stored anywhere near as much energy as a propane bottle, so you run out of electric "fuel" sooner than propane. It's the fuel tank size/capacity that makes the difference. A 20# propane tank is physically about the same size as 2.5 12v batteries, whether lead-acid or lithium.

I should have read your explanation before I read Lou's message.

Still makes me wanna stick with propane refrigerators in RVs.

-Don- Reno, NV

 

[DonTom]

Some folks are scared of propane..

I can understand that after what happened to Bill, HueyPilotVN. But it was never shown if his had all the safety recalls on his model and the exact cause was not yet figured out, AFAIK.

Also, it most likely could have been prevented with a Fridgedefend as I have in my Y2K motorhome.

-Don- Reno, NV

 

[Lou Schneider]

I really cannot say I know, but I have a difficult time buying that.

Besides the obvious fact that when boondocked the propane level doesn't drop a noticeable amount after a few days and nights of only running the refrigerator. But I think most would notice that 8-amp draw or whatever on their house batteries. But I also realize that 8-amps is not 100% of the time, just when the compressor is running. But on a warm day, what would that duty cycle be?

-Don- Reno, NV

Absorption refrigerators use 300 watt heating elements to power their cooling units. Compressor refrigerators draw less than 1/10th that amount.

The reason you don't notice the propane consumption of an absorption refrigerator is propane (or any other hydrocarbon fuel) stores so much more energy per unit of weight and volume than a battery. The same principle holds true for internal combustion vs electric vehicles which is why large electric vehicles are impractical, Tesla's claims for it's a semitruck notwithstanding. A 30 MPG ICE vehicle can travel 300 miles on a 10 gallon tank of fuel weighing 61 lbs and having a volume of 1.34 cubic feet. An electric car battery capable of going the same distance weighs 1400 lbs and consumes 140 cubic feet of the car's space.

 

[DonTom]

Compressor refrigerators draw less than 1/10th that amount.

Less than 30 watts?

I recall the Thor motorhome I first looked at said right on the refrigerator door that the current draw was 8 amps. And that was a small compressor refrigerator. 13V times 8 amps=104 watts. Yeah, still less than the 120VAC element (330 watts, IIRC) but still a lot more than 30 watts. But not sure about the duty cycle. I assume the compressor is not always running.

-Don- Reno, NV

 

[Lou Schneider]

Less than 30 watts?

I recall the Thor motorhome I first looked at said right on the refrigerator door that the current draw was 8 amps. And that was a small compressor refrigerator. 13V times 8 amps=104 watts. Yeah, still less than the 120VAC element (330 watts, IIRC) but still a lot more than 30 watts. But not sure about the duty cycle. I assume the compressor is not always running.

-Don- Reno, NV

Using my Magic Chef 10.1 cu ft refrigerator as an example: 297 kWh annually divided by 365 days a year is 813 watt-hours a day. Since there are 24 hours in a day that is an average draw of 34 watts. About 3 amps continuous from a 12 volt battery. Not all that much more than the 0.5 amps or so a propane refrigerator uses for just it's control board. The actual peak power (what is listed on the nameplate) is higher but as you noted the compressor isn't on all the time.