Running a 3 way fridge off leisure batteries....your experiences?

So, after a 10 day off grid holiday in sunny clear blue skies every day, I'm pondering on utilising the solar/batteries to run my fridge during the day, for say 8-12 hours (on suitable daylight only) instead of using the gas, so switch to gas at night or continue running from batteries if sufficient capacity (assuming it's already cold) Gas in the UK is becoming a cost limiting factor to cheap off grid camping and removing that as a factor may help cut gas costs by 50%.
I have 600w (6x100w) panels in series and am seeing a consistent 135v input to the controller (Epever 60 Amp) when the sun comes out. 2x 180Ah AGM's in parallel and 1000w PSW inverter.
Fridge is a 3 way:
130w @ 14.4v when fed from starter battery (engine running), so ~9Ah
125w @230v when fed from EHU, so ~0.5Ah
125w @230v when fed from inverter = ~12Ah

If I'm understating the the theory correctly, running the fridge for 12 hrs on battery would take ~144 Ah from the batteries, 60% SOC, but if i was getting good solar charging at the same time, or atleast some of the time then the SOC would be higher.

Has anyone done (or do) this

MickyBoyMH said:

So, after a 10 day off grid holiday in sunny clear blue skies every day, I'm pondering on utilising the solar/batteries to run my fridge during the day, for say 8-12 hours (on suitable daylight only) instead of using the gas, so switch to gas at night or continue running from batteries if sufficient capacity (assuming it's already cold) Gas in the UK is becoming a cost limiting factor to cheap off grid camping and removing that as a factor may help cut gas costs by 50%.
I have 600w (6x100w) panels in series and am seeing a consistent 135v input to the controller (Epever 60 Amp) when the sun comes out. 2x 180Ah AGM's in parallel and 1000w PSW inverter.
Fridge is a 3 way:
130w @ 14.4v when fed from starter battery (engine running), so ~9Ah
125w @230v when fed from EHU, so ~0.5Ah
125w @230v when fed from inverter = ~12Ah

Click to expand...

The issue with a 3 way fridge running on 12V is the heater coil is usually much lower wattage, thus the fridge can maintain temp but not necessarily decrease fridge temp.

The AC powered coil is usually much larger. I see you tested watt draw but something probably isn't right with your figures from my experience. With a larger sized AC heater coil, you should see a much higher wattage draw due to the coil and inverter losses.

Best performance is always on gas, the reason is the btu's in propane is quite high compared to the heating coils on AC or DC.

MickyBoyMH said:

If I'm understating the the theory correctly, running the fridge for 12 hrs on battery would take ~144 Ah from the batteries, 60% SOC, but if i was getting good solar charging at the same time, or atleast some of the time then the SOC would be higher.

Click to expand...

A full day will take 288Ah. Your panels need to produce that much. 288Ahx12V=3,456W

3456 divided by the 600W of panels= 5.76 hours of full sun at full output of the panels which won't happen.

This is just to run the fridge, not charging the batteries or running other devices. If you run on 12V just during the day, it will most likely take the entire yield of the panels to just run the fridge if you figure 60 to 80% yield. Take today, I am readying the camper for a trip and see I'm getting 150W from 600W of panels because it has been overcast all day.

MickyBoyMH said:

Has anyone done (or do) this

Click to expand...

You would be better served with a DC compressor fridge or continue using gas when parked. When traveling, the 12V will maintain temp, but not really provide cold.

For my truck camper, we use a Dometic CFX95 fridge/freezer in place of the backseat in the truck cab. I can run off the truck or off the camper solar system. We rarely use the 3 way anymore. If you get some hot days, the absorption fridge will struggle. Fans help but that draws more power too. I'll probably pull the 3 way out at some point if I find a DC compressor fridge that fits the hole.

What you propose can be done, don't get me wrong. There will be days you will probably be short on power and may have to conserve in order to make it thru the night. It would depend on how much management you want to perform.

x2 on the compressor fridge.
Boats don't use LPG for refrigeration. With ~700W and 300Ah(12V) of LiFePO4 of solar I run 2 coolers, one as a freezer and the other as a fridge. 24/7 for months at a time.

I'm guessing that you have the six panels laying flat on the roof of your RV? When positioned in a off-optimum angle like that, don't expect to get more than ~60% of rated output, and that's near noon. Since you are quite far north, I'd expect 60% to be rather optimistic?

Instead of focusing attention just on the voltage coming into the system, you really need to be paying attention to the amperage, which is going to be rather low with the acute angle your panels are to the sun.

Going with Zwy's numbers; (3450W/5sunhours)/60% = 1150W, basically double what you have right now. Look into getting grid-tie panels rather than more 100W ones. You get lots more W/£. Three or four 60-cell panels should equal the voltage of your five 100W panels. With two 180Ah batteries, you really need about 45A of charge current coming in. If you look at what your typical amp production is right now, you will have a clear idea on how much you need to expand.

With good battery management and selecting manually the DC12v option for the fridge when the solar yield is good, is an viable option. This is subject to a probable lower cooling performance of the 3 way, thus in hot weather where solar is available, the poor performance of the fridge in these conditions will be worse than gas operation.

An expensive solution is to replace the absorption fridge with a 12v compressor fridge. Your solar setup will easily provide the necessary power.

Mike

My RV refrigerator has only gas/120vac options. I run it on AC during the day as long as I don't mind the heat generated by the inverter. On super hot summer days, the heat from the inverter can be too much. As I recall, my refrigerator uses about 375 watts on AC (I think, I didn't write it down or take a picture). When I have excess PV production, I have no problem switching the refrigerator to AC.

After PV production decreases, I switch back to gas.

When my absorption refrigerator dies, it will get replaced with a 12v compressor refrigerator.

Thanks for replies so far.
The trade off between saving £1/day against managing the power consumption, which could be a hassle on its own.
The gas does work very well and i wouldn't want to risk food spoiling.
In away again next week, so the best test i guess will be to see what happens one day.....i am curious to push my system to see how it performed. At the moment I'm not seeing the battery drop below 100% at any time of the day or night, but to be fair i have been away in the perfect summer sun.
Would it be frowned upon if i plugged my EHU to the inverter socket, turning off all other unwanted demand sources, instead of wiring a new supply to the fridge? The MH would then have AC for the fridge only.

MickyBoyMH said:

Thanks for replies so far.
The trade off between saving £1/day against managing the power consumption, which could be a hassle on its own.
The gas does work very well and i wouldn't want to risk food spoiling.
In away again next week, so the best test i guess will be to see what happens one day.....i am curious to push my system to see how it performed. At the moment I'm not seeing the battery drop below 100% at any time of the day or night, but to be fair i have been away in the perfect summer sun.
Would it be frowned upon if i plugged my EHU to the inverter socket, turning off all other unwanted demand sources, instead of wiring a new supply to the fridge? The MH would then have AC for the fridge only.

Click to expand...

I don't see a problem doing that.

Feeding a 230 AC RV distribution system with multiple appliances and outlets needs the following to fully comply with UK regulations.
The Inverter must be a type that has neutral to protective earth bond within the Inverter. The inverter case 'earth ' must be connected to vehicle 'earth', chassis, frame , metal body, as should the 230 v protective earth conductor of the 230 v system. As near as possible to the inverter an inline RCD should be installed feeding all outlets and appiances connected.

Mike