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3 way fridge draining engine battery


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Hi all.

I've just bought a 02 fiat ducato moncoya. I have it plugged in to mains when parked to keep the fridge fresh and cold but I got to it the other day and found the fridge was off. I checked 230v mains, that was on but the fridge wouldn't switch on. I removed the fridge to get at the electrical box on top of it and found that I hadn't the 12volt supply. I checked the two leisure batteries and I had 12 volts . So then I went to the ignition and it was dead 0 volts...

My questions are,

1. how does a 3 way fridge work, is there a supply signal from the key switch to run it off the batteries when the engine is running?

2. Should the battery charger charge the engine battery while the camper is plugged in?

The fridge is an electrolux rm7505.

Any help would be greatly appreciated as I am new to campers.



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The RN7505 is connected to both the battery directly, and to the vehicle's alternator D+ terminal, and sorts itself out.


See manual pages 19 20 https://www.electrolux.ie/support/user-manuals/?q=rm7505


The live feed only works the electronics [its brain not chilling circuit] so does not chill the fridge, the supply from the alternator's D+, terminal when available, supplies the power to chill the fridge.


So the fridge electronics is live and able to respond to what powering supplies are available, but ensures the high current drain chilling would take is only available whilst the alternator is spinning adequately.



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Thanks Guys. I need to check to see if the 12v supply is connected to the engine battery or the leasure battery. That manual was very helpful.


Does anyone know if the engine battery should be charging while the camper is plugged in?

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I think your van is probably a Moncayo? but you haven't said which model or year - which might make a difference.


The following comments are not offered as "expert" advice: there are contributors to this forum with far greater electrical knowledge than me, but are just some "basics" to get the ball rolling.


First, the fridge. You say the van has been connected to 230V more or less since you got it, and that you have left the fridge on during this time. The RM 7505 is an AES (automatic energy selection) model, so it will look for its energy source prioritising first 12V, then 230V, and then gas. So, when the engine is running it will switch to the 12V supply, if that is absent it will switch to the 230V supply, and if both are absent it will try to switch to gas. If none are available, it will switch to a fault mode.


It will have two separate 12V supplies. One to its controls, which is more or less permanent and is supplied from the habitation battery/on board charger/power pack, and the other to the 12V heating element, which is only fed when the engine is running. How these are fed and fused will depend on whose electrical equipment is installed. It will therefore be helpful if you can identify the maker and, if possible, the model number of your control panel, 12V fuse/distribution board, and on board battery charger/power pack.


In principle however, there will be a "normally open" switching relay (possibly two) within the van electrics that will energise (usually) two 12V supplies to the van side electrics: one to charge the habitation battery, the other to supply the fridge heating element (which, counter-intuitively, does the cooling).


The relay/s is/are switched to energise those two supplies by a low current signal from the alternator (the so called D+ terminal), that is only live once the alternator is producing current. Once the engine is running the D+ signal will switch the relay/s to close its/their contacts, and feed power from the alternator to charge the habitation battery and feed the fridge 12V element. When the engine is stopped and the alternator is no longer generating current, the relay/s will automatically open to de-couple the starter and habitation batteries, and to prevent the fridge 12V element draining the starter battery.


The 230V heating element can only be fed if the 12V control circuit is live, and the 230V mains connected.


Gas, of course, requires a supply of gas to the fridge - so a gas cylinder/tank with gas in it, and all supply cocks open.


1) So, first and simplest, disconnect the mains supply, and check all 12V fuses, noting any that have blown, and replace them like for like, and then re-check for voltage to the fridge connection box. If all is then OK and the fridge works, the immediate problem is solved, so go 2) below.


2) First check and correct the starter battery electrolyte level, and then get it on charge as an urgent priority - as it will undoubtedly have suffered some damage from being run flat, and may have effectively been destroyed. If/when you get it on charge I would suggest you monitor its progress every hour or so, especially how hot it is getting. If it seems hot, stop charging it and get it to a supplier to test - in the expectation that it will have to be replaced. Or, if you prefer, just cut out the "middle man", disconnect the van from mains immediately (so that there is no possible charge from the on board charger) and take the battery straight for testing. Now, with a new/fully charged starter battery, go to 3) below.


3) Now turn your attention to the blown fuses noted at 1) above. Carefully check the circuits fed by the blown fuses for damage or faults that could have over-loaded the fuses, and correct any you find.


If the above doesn't permanently fix or identify the problem, it's over my head, but I'm sure others will be able to assist.

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