Running absorption fridge from 12V

[VagabondDK]

I have a nearly 20-year old Thetford model N100 EL-L 3-way absorption fridge in my motorhome where I live full-time mostly off-grid. During the summer season I have plenty of solar-power and would like to run the 3-way fridge on 12V during the day and gas during the night, especially now with the higher gas-prices.

I have a Schaudt EBL99 electro-block and from my novice reading of its electronic diagram, as well as the excellent posts by autorouter on this forum, it looks like I just need to change the wiring on the EBL99 and insert a 20A fuse. Specifically, in block 1 of the EBL99 I need to change pin 1 into pin 4, which is intended for a compressor fridge.

I have some questions that I hope autorouter or someone equally competent will answer:

1) Is my understanding above correct? Will it make the fridge run on 12V from the leisure battery when the engine is off, and then automatically switch to run off the car's alternator when the engine is running?

2) I can't find the official specs on how many amps it will draw. Some people say 10A. Is that right?

3) If I rewire the EBL99 as described above, will the 12V fridge constantly be on, or only when I turn the dial on the fridge to the battery-position? I want to be able to turn it off during the night, cloudy days, winter, etc.

4) If I forget to turn off the 12V on the fridge, does the EBL99 shut-off when the battery gets too low, so it doesn't destroy the battery?

5) Is the 12V heating-rod only made for short-term usage? Will it burn out if it is used 10 hours a day for 6 months a year?

6) Is it possible to use both gas and 12V at the same time, the idea being to constantly run a small "pilot flame" along the 12V heating element? The reason is that when my gas-burner is turned off for a while, it has problems staying on afterwards, and I have to insert a piece of plastic to keep the gas-dial pressed down for 15-30 minutes, until it can stay on by itself. I thought I might avoid that by keeping a small pilot flame on all day along with the 12V.

7) I need a special tool to remove the electrical pin on the EBL99 connector without destroying it. In another post by autorouter there is a link to such a tool. I don't know if I can find such a tool. And I can't even see the locking pins. Is there any other way to remove the pins without a special tool? Any tricks?

Thanks in advance!

 

[autorouter]

1) With the old or the new wiring, the fridge will not run on 12V unless the dial is on the 12V position. If the dial is on the 12V position, the fridge will run on 12V from the alternator/starter battery when the engine is running, and will run on 12V from the leisure battery (via the 20A fuse) when the engine is not running.

2) not sure but sounds about right. My fridge, a large fridge/freezer, takes 14.4A.

3) It only uses 12V when the dial selects 12V.

4) Yes it will shut off, not sure what voltage, it's quite low but high enough to prevent damage.

5) don't know, but I suspect it is the same construction as the 240V element, so I wouldn't be too worried.

6)I don't think it's feasible. The fridge coolant circuit requires a specific amount of heat. I think the gas flame is a constant power, and doesn't have a pilot light, but I don't know about all the different models, so maybe someone else will have a better idea.

7) If you look at a pin before it's inside the shell, it's easier to see.

Mate N Lok Male Pin Terminal

Mate N Lok male pin crimp terminal for 0.5-2.0mm² cable. Tinned brass. Use with our range of Mate N Lok Universal multi-way connectors.

www.12voltplanet.co.uk

You can see the two barbs curling out from the sides of the pin. The 'special tool' is simply a metal tube of the correct diameter to hold in the barbs while the pin is pulled out backwards from the shell. It's possible to push in the barbs with some thin probes, I used a couple of fine jeweller's screwdrivers. You might have to push out the barbs again when you are inserting it into the other hole.

The reason it's not a very popular method of powering the fridge it that it's really easy to forget and run the leisure battery down. You may know that later Automatic Energy Selection (AES) fridges have an 'S+' terminal triggered by an 'S+ terminal on some solar controllers, to switch from gas to 12V, and back to gas when the sun sets or it becomes cloudy. It checks the solar power output every 30 minutes to make sure it's powerful enough. You would b doing that job manually.

 

[VagabondDK]

Thanks very much for the quick and detailed reply, I greatly appreciate it!

After I had written my post above, I realized that in order to have both 12V and gas turned on at the same time on the fridge, the dial would have to be in two positions at once But it might be possible by first lighting the gas-burner, then inserting a piece of plastic to hold the gas-dial down so it doesn't turn off, and then turning the other dial to 12V.

I will go to a car-part store in a few days and see if they have the tool I need to remove the pin.

Interesting that they make fridges that automatically switch between solar and gas using a control-signal from the solar-charger. I didn't know that. But it makes sense as it's like the D+ signal from the alternator that signals the car engine is running.

I have a few additional questions you might know the answer to:

A) As mentioned above, when the gas-burner has been off for a few hours and I want to turn it back on, I have to keep the gas-dial pressed in for maybe 15-30 minutes and sometimes longer, otherwise the gas-burner turns off again. I use a small piece of plastic for keeping the gas-dial pressed in. Do you know what is causing this and is it easy to repair? (If you have an elaborate explanation, perhaps it is better if you write it in a separate post here on the forum and provide a link, so others can more easily find it in the future.)

B) Is it dangerous to force pressure on the gas-dial like this? Does it prevent the safety mechanisms from working properly? So if the flame goes out, the gas will still come out and possibly cause an explosion? Do you know?

C) My fridge doesn't cool as well as it probably should on gas. I got a new gas-burner installed 2 years ago, and even when it was brand new, it still didn't cool that well. The insulation-seal around the door fits tightly, as I tested it just a few days ago with a piece of paper. But even at the highest gas-setting, the fridge doesn't get much colder than 10 C, while 230V gets a much lower temperature in the main fridge down to -5 C. On both gas and 230V the freezer goes well below -10 C. So it seems strange that the main-cooler gets much colder on 230V than on gas. Several people have said it should be the other way around.

Thanks again!

 

[Northernraider]

The 3 way fridge 12v supply isn't actually meant to cool the fridge . Its only really to try and maintain the temperature whilst on the move. I wouldn't expect it to be very good running on 12v for hours on end. I found most of mine to be pretty poor on 12v . If its not cooling great on gas its most likely needing the flu abd burner cleaned out as it cokes up especially of using LPG

 

[VagabondDK]

Thanks for the suggestion.

The funny thing is that when I have driven an entire day and running the fridge on 12V, it actually cools just as well as if it was running on gas, and it can cool it down from room-temperature, so the ice-box was maybe -10 C after a whole day of driving.

I don't think the weak cooling effect when running on gas is due to the gas-burner or chimney being dirty - because even after the gas-burner was replaced and the chimney was cleaned professionally, it still didn't cool very well. I saw someone on YouTube who had a similar problem, and he turned the fridge upside-down for a day or so, which apparently did something to the chemicals, and then it worked fine again. I don't know if that makes sense? I can't really do that myself, so I would need to pay someone to try it.

Regarding the terminal extraction tool to detach a wire, I went to a few local shops and they don't have it. I can buy a set from Amazon for about 10 Euro.

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[Jimbohorlicks]

For your pilot light going out ,it sounds as though it just needs a clean up of the thermostat tip or the pilot light moving closer to the thermostat in the burner area.thecreason it's going off is due to it not getting hot enough to open the gas valve.sometimes the thermo couple tip just needs a de coke.

 

[VagabondDK]

Jimbohorlicks Thanks, that makes sense! Unfortunately I cannot get to the back of the gas-fridge from outside, because it is a stupid "modern" design by Hymer where they covered the lower air-intake with the big plastic rear-bumper. So I would need a professional to take the whole fridge out and clean it / adjust the thermostat. But at least now I know what is probably causing it.

 

[pappajohn]

B) Is it dangerous to force pressure on the gas-dial like this? Does it prevent the safety mechanisms from working properly? So if the flame goes out, the gas will still come out and possibly cause an explosion? Do you know?

Not a good idea using anything to hold the gas knob in.
Yes, it will defeat the safety system.
You press the knob in to temporarily defeat it while the thermostatic bulb heats up enough to keep the valve open on its own.
The idea being if the flame goes out the gas valve closes in seconds.
Running on battery..... .yes, it will but only for a few hours before the battery is flat.
The fridge may draw around 10 amps per hour from the battery so a 100ah battery will last around 5 hours at best

 

[Lenny HB]

Is the 12V heating-rod only made for short-term usage? Will it burn out if it is used 10 hours a day for 6 months a year?

More of a concern would be your batteries unless you have a very large battery banks and lots of solar it's not practical, 2 hours a day is more realistic.

I use a Votronic Solar regulator which has a AES output which is connected to the S+ terminal of the fridge. When the batteries are charged and there is plenty of solar the fridge switches to 12v, it doing 30 min blocks turning back to gas every other 30 min so as not to flatten the batteries. On a good day in Spain fridge may run for 2 to 3 hours total on 12v.

I have 3 x 78ah Gel batteries and 300 watts of solar.

With your setup and the fridge not auto re-lighting on gas what you are proposing is not practical.