# Fridge on Vehicle battery



## IPreston (Sep 26, 2013)

OK, numptey questions.

When I switch my Dometic fridge onto the vehicle battery is it on all the time or only when the engine is running?

Left it switched on whilst on the ferry, no problems but it got me thinking.
:roll:


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## bigcats30 (Aug 13, 2012)

It should only work when engine is running mate


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## sideways (Jun 2, 2008)

it takes a lot to run on 12v and the thermostat doesn't work its just flat out,thats why it only works when running. it will keep stuff ok on the dover Calais but not on the Southampton spain I just leave it on gas (ducking as I type)


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## Penquin (Oct 15, 2007)

There is a relay which only allows it to operate on 12v when the engine is running, the CC reckon that a fridge takes about 8a in their handbook when running - which seems a lot to me but it makes the point (which is probably their idea.....)

You should not leave the gas on - it is against the T&C on the ferry and is dangerous - at Plymouth they check that the cylinders are actually switched off in the pre-boarding checks at times - we have been checked a few times for that......

A fridge will survive quite OK without running for the duration of the ferry crossing - even the 24 h Plymouth/Portsmouth to Santander if it is properly cooled in advance and filled as full as possible with e.g prefozen milk type bottles 3/4 filled with water and frozen in a domestic freezer.... carrying such goodies as bacon in the icebox also helps.....

Dave


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## listerdiesel (Aug 3, 2012)

Most Electrolux/Dometic fridges run at 100W input power on 12V, which is about right at 12.5V.

I'd always check that the fridge is off before assuming so.

Peter


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## bigcats30 (Aug 13, 2012)

sideways said:


> it takes a lot to run on 12v and the thermostat doesn't work its just flat out,thats why it only works when running. it will keep stuff ok on the dover Calais but not on the Southampton spain I just leave it on gas (ducking as I type)


Just freeze everything when you go

also add a couple bottle of frozen water/milk etc

Surely you only take 24hrs worth of food seeing as you can shop...for cheaper...when you arrive


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## Boff (May 10, 2005)

Hi,

the fridge would run with about 8.5 amps.

Even a pristine and fully charged 100Ah battery would be damanged beyond repair after just about 6-7 hours. There is a reason why MH manufacturers allow 12v operation only while the engine is running.

Best Regards,
Gerhard


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## kernowblokes (Aug 28, 2013)

For all the above reasons they go off when with engine when on 12v.

As for keeping stuff cool/cold. We used the overnight Plymouth - Roscoff service quite a few times with our old T4. and as we usually had a long day of driving ahead the solution was precooked frozen meal in frige just before leaving home. dont open fridge till after fwrry crossing result perfectly cold fridge next morning when back on 12v and easy dinner for first night stop. Perfect!


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## Easyriders (May 16, 2011)

As others have said, the 12v will only work when the engine is running.

We always freeze a casserole or chilli in a plastic container, and put it in the fridge.

It keeps the fridge cold for ages, in fact it's usually a bugger to defrost if you want to eat it the first night abroad!

If you're worried, invest in a cheap fridge thermometer from e.g. Lakeland.


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## whenIretire (Mar 16, 2012)

Our fridge will carry on running on 12v even with the engine off.

I found this out the hard way in France when I forgot to switch from 12v to gas when we parked up for lunch. 

Came back to the van a few hours later and the leisure battery was completely dead. We were planning on using an aire that night but had to swap to a campsite with hook up. Admittedly it wasn't in the best condition before this and was only 70ah. I've now changed it for a new larger capacity one and don't want the same to happen again so don't currently use the 12v option.

So I'm not sure if it's wired up incorrectly or if it's likely to be a duff relay, or if that's just the way it works.

So as Peter says, check, and don't assume that it will be off.


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## Pudsey_Bear (Sep 25, 2008)

Not sure if most fridges are the same, but our fridge freezer is mega efficient on the 12v, so much so that we didn't always switch it to gas when we stopped as it was keeping stuff chilled to the correct temps in either section.

Actually we kept forgetting this MH lark is too complicated at times


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## dovtrams (Aug 18, 2009)

I am more than surprised that fridges run at approx 8 amps. If that is the case how come 16 amp EHUs are not blowing up all over the place when you then add all the other electrics that are on in a MH. Especially the 1800watt heating ie 7 amps.

Expert advice required, as k&l say, this MH business is sometimes over complicated.

Dave


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## Steve_UK (May 18, 2012)

8 amps @ 12v = approx 0.4 amp @ 240v in theory. Probably about 0.5 or 0.6 amp in real life.


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## Pudsey_Bear (Sep 25, 2008)

dovtrams said:


> I am more than surprised that fridges run at approx 8 amps. If that is the case how come 16 amp EHUs are not blowing up all over the place when you then add all the other electrics that are on in a MH. Especially the 1800watt heating ie 7 amps.
> 
> Expert advice required, as k&l say, this MH business is sometimes over complicated.
> 
> Dave


Not an expert, but 12v and 230v are totally different animals, which complicates things somewhat, cable sizes on 12v are much bigger, as you have to account for losses per metre,


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## IPreston (Sep 26, 2013)

Thanks for the answers, is as I thought

V= IR

Transpose as required


:wink:


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## teemyob (Nov 22, 2005)

On some Elektroblocks, you can fit the fuse to allow the Fridge to run on 12v Manually. But as Boff said, 100ah new battery will be drained and harmed.

It is okay for shorter periods or with lots of batteries and Solar/Wind.

TM


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## tugboat (Sep 14, 2013)

P=IV (Watts=Amps x Volts).


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## listerdiesel (Aug 3, 2012)

tugboat said:


> P=IV (Watts=Amps x Volts).


Tuggers:

Lest we all forget:

Watts = Volts X Amps DC, whatever tags you put on them

VA = Volts X Amps AC.

To convert VA to Watts, multiply by the Power Factor (pf)

Having P for Power instead of Watts, I for current instead of A and E for Volts instead of V confuses many.

People like me who have been in electronics all their life will use either. but mentally I still think in terms of Watts, Volts and Amps. My multimeter is scaled as such so using different symbols is very confusing.

Peter


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## whenIretire (Mar 16, 2012)

teemyob said:


> On some Elektroblocks, you can fit the fuse to allow the Fridge to run on 12v Manually. But as Boff said, 100ah new battery will be drained and harmed.
> 
> It is okay for shorter periods or with lots of batteries and Solar/Wind.
> 
> TM


TM

Do you know how to reverse this ie so that the fridge won't run manually on 12v?

I've googled various things to try and find out how to stop the fridge running on 12v when the enginge is off or to see what the fault is to no avail.

So at the minute I'm left with not running on 12v in case I forget to switch off, or paying someone to fault find it for me.

Cheers

ETA - I've sorted it.

Went and had a proper look at the Electroblok. Where there is a fuse for a fridge there is a blooming great big warning triangle with an exclamation mark in it and the wording 'fuse only with AES fridge'

Now assuming that AES is something to do with auto switching between sources, mine does not have that function and so should NOT be fused.

Fuse taken out and it now works fine on gas, EHU, 12v with engine running. But NOT 12v with engine off. Perfect!

Me and my expensive 150ah agm battery thank you TM. 

The fuse doesn't match the others in the block so it looks like something the previous owner has done. No wonder the original battery was in such a poor state, it had probably suffered considerable damage.


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