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post #1 of 14 (permalink) Old 16-12-2009, 00:33 Thread Starter
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Fridge relay / switch decision

I have an Electrolux RM212 fridge freezer that i am thinking about wiring up through a relay.

I was wondering what the benefit of having a relay on this fridge is?

The amperage drain is 8amp...hardly a vast amount.

Can i wire a switch instead, so that i can choose to have it running on 12v if i need to?

Or is there some aspect of fridge power drain that i am not fully aware of?

The fridge has a three way switch on it, 12v, gas, mains. I understand that this has to be set to the selected power source before that power source can have any effect on the fridge, but if a relay is wired then i can only utilize the 12v switch when i am going to drive somewhere. Which is somewhat limiting. If i am running low on gas i would ideally like to be able to use 12v for a few hours as a safeguard option.

Has anyone got any experience of having this option available? Or has anyone tried this type of thing before?


BTW - i have 6x65ah leisure batteries (390ah total) it is a possibility for me to run this fridge with my power source.
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post #2 of 14 (permalink) Old 16-12-2009, 00:53
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As long as you appreciate your large battery bank goes from full to 50% in one day with no other loads, fine.

The other aspect with many fridges (not sure about that one) is that the cooling power running on 12V is less than gas or mains.

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post #3 of 14 (permalink) Old 16-12-2009, 02:34
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Normal practice is to wire the 12v side via a relay which only works when the engine is running, It would be no problem to put a override switch into the circuit,
The only problem is when you forget to switch it off and it flattens your batteries

I do not know what charging system you have but it could take around 40 hours to fully recharge them

Alan H
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post #4 of 14 (permalink) Old 16-12-2009, 10:15
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With the batteries you state you have you may be in danger of overloading your 'van!
Normally a fridge is wired so that the 12v operates from the base vehicle electrical system through a relay. The relay is wired so the operating coil only switches when the ignition is switched on, ie from the aux side of the ignition switch, with the load side from the battery through a fused connection.
However, with a shed load of batteries you say you have it is feasible to also wire to the leisure batteries via a fused connection. You will need to fit a change-over switch, suggest two pole- 3 way- centre off, to change from van to leisure batteries; and because of the load I suggest you also wire the battery side through a relay to minimise the load on the switch. Relays close quicker than a switch and are designed for heavier loads.
Make sure you get suitable relays, 12v coil, load rating twice actual estimated load. it would also be sensible to fit a voltmeter to monitor the battery discharge as it will take a long time to recharge 6 batteries!
(Usual disclaimers apply to this post.)
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post #5 of 14 (permalink) Old 16-12-2009, 10:18
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As I understand it, the 12v setting is only to maintain the already cold fridge temperature whilst driving. Normal running options while 'camped' are gas or 230v. Apart from the battery comments already made I doubt if running on 12v will maintain a good cold fridge temp.


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post #6 of 14 (permalink) Old 16-12-2009, 10:56
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I echo concerns of other comments... the 12v side of a leisure fridge only 'maintains' the temperate, it is not built to refridgerate. So if your fridge is room temperature, its cooling effect on 12v will be minimal if non existant.

For running a fridge on 12v, you need a compressor type fridge.
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post #7 of 14 (permalink) Old 16-12-2009, 11:19 Thread Starter
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The charging system is a 90 amp Sterling Alternator to Battery Charger...should charge 'em up in less than 40 hours!!! As well as a standard van mounted 6amp charger for overnight charging on a hook-up. An 11amp Absaar charger for running off of our generator in emergencies...we may upgrade this to a 25-40amp depends on if we come to use it more often than just emergencies.

The Sterling has a split charge diode built in to it, which does the job of a split charge relay....I have a battery selector switch built in to the distribution board (3-pole, centre off) you think i will need a relay as well? Are you are suggesting a split charge relay, to split the charging route...if so, the diode has that covered...if not please elaborate...i am all ears...thanks.

I have a battery condition meter...switchable from engine to leisure banks. I'm thinking of getting a Nasa digital battery meter...with load display and time until discharge...very handy.

I was thinking of fusing the battery charging run at the battery end, in between the battery and charger and in between every battery on the battery bank positive chain (to minimize risk of a short dropping every battery's charge)

With regards to fridge fusing BJT...i was simply thinking that if i have to flick a switch to change power source on my fridge every time i want to change it, as i do have to because i have a three pole switch (12v, gas, mains)built in to the fridge itself, it would be simple to have another switch located immediately above allowing me to route 12v power to the fridge on demand. Not for any extended period. Just in an emergency.

The scenario that made me think of this was this...We are going to live in the French Alps for the winter...sub-zero every day and night for months...if one night we find our gas to be low and cannot replace our tanks until the morning, or at worst at on a Saturday night and we have to wait until Monday morning, it would be useful to be able to use 12v to keep the fridge cold...whilst the low level gas can be used to keep us warm. This is very unlikely to happen but who knows.

Fatalhud...thanks for the override idea...that seems to be the best of both worlds. Relay as standard, with the option to use 12v if absolutely necessary.

Thanks so much to all who replied. Ingram...i hadn't thought of that...12v fridge runs less efficient than mains or gas? I will have to ponder that one.

Thanks again.
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post #8 of 14 (permalink) Old 16-12-2009, 14:46
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If you are going to live in the Alps over Winter and run out of gas you will need to make sure the water and waste tank and connecting pipes are not liable to freeze; plus the water heater will need draining down. As for the fridge, bung the contents outside in a secure box, that will keen them cool!
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post #9 of 14 (permalink) Old 17-12-2009, 13:24 Thread Starter
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Thanks for the advice...our fresh water tank (250 ltr) is internal and our waster water tank is housed in a heated, insulated (double wrapped in bubble foil insulation, box lined with 50mm celotex, box walls made of sandwiched 6mm ply, 50mm foam, 6mm ply) water sealed extension slung under the van. It is connected on the top edge to the under side floor of the van, and heated by a leg of our blown air heating system, with a re-entry for the blown air coming up through the floor so no hot air is wasted.

There are two drainage valves...both are housed in the heated box and both are accessible from a small hatch in the floor of the van. One is a tap that drops water through a small hole in the underside of the box...and the other is a hose connector that we can run a length of hose from if we need to drain our waste water in a specific area. No runs of exposed pipe, no exposed drainage taps.

We have two water heaters a carver cascade 2 that is purely a backup and is insulated from the outside by means of a sliding 50mm Celotex wall that seals it from the outside until we need to use it. The other is a Morco that although internal, is room sealed in its own insulated cupboard that extends to the floor of the van with drop outs at floor level, and a sliding vent in the side wall that allows us to seal this off from the outside as well...if the temp drops really low.

We have been planning this trip for quite some time!!!
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post #10 of 14 (permalink) Old 17-12-2009, 14:22
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This sounds like, one well thought out project
Nice to see some pictures when its done

Alan H
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