# Wiring Dometic Fridge To Work Off 12 Volt Advice



## gnscloz (Oct 4, 2008)

Hi we have swift sundance on x250 cab with dometic 3 way fridge, 
We now have 200 watts of solar and I'm sitting here trying to think of a way of utilising the spare electric, feeding 12 volts to fridge comes to mind, as anyone undertook the task, my handbook states 12 volts to fridge only works with engine running.
Mark


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## grizzlyj (Oct 14, 2008)

Hiya

Can you find out how many amps your fridge needs when on 12v?

I thought a normal (non-compressor) 12v/220v/gas fridge was too innefficient on 12v to be sensible when the engines off?

Don't know though 

Jason


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## Zebedee (Oct 3, 2007)

Not sure I quite understand here?

If the solar panel keeps your batteries charged up, surely that's all there is to bother about . . . it's doing its job??

The fact that there may be a surplus of electical power doesn't mean you are losing out if you don't use every scrap . . . . 

. . . . or am I missing something?

Dave


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## gnscloz (Oct 4, 2008)

Zebedee said:


> Not sure I quite understand here?
> 
> If the solar panel keeps your batteries charged up, surely that's all there is to bother about . . . it's doing its job??
> 
> ...


Hi Dave thanks for response 
Just thinking when not on hook up fridge works off gas, the solar panels on average get batteries back charged lunch time, so in thery there's a wasted ammount of solar power during afternoon, do was wondering if it was possible to get fridge working on 12 volt, we are hardly ever on hook up now. 
Mark


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## gnscloz (Oct 4, 2008)

grizzlyj said:


> Hiya
> 
> Can you find out how many amps your fridge needs when on 12v?
> 
> ...


Hi Jason thanks for response never thought of it that way will
Have to do some research thanks


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## sideways (Jun 2, 2008)

The fridge thermostst does not work on 12v it just runs flat out all the time and crucifys batteries thats why it only works when your running.


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## Zebedee (Oct 3, 2007)

Hi Mark

I'm trying to convince myself about solar panels, but it won't be easy on our van since there is so little available room on the roof. I would have to link several small ones, and scatter them around the flat (and still free) bits of the roof! 8O 

I can see your point of course, but it seemed simpler to let the panels keep the batteries topped up, and draw whatever current you wanted from the batteries as usual. Much easier than firtling around in the innards with bits of wire and switches.  

I have no practical experience at all, so it was a purely theoretical suggestion. :roll: 

Dave


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## trevorf (May 16, 2005)

On 12V your fridge will draw about 10 amps. Thats about your entire solar output in full sun at midday. Early or late in the day or when a cloud comes over you will be draining your leisure batteries.

The mains element in a fridge is around 600W. The 12V element only around 120W so much less efficient at cooling. They rely on increased air flow due the van moving ie engine running and travelling. Even then, no where near as much cooling as mains or gas.

Gas is the most efficient method to run the fridge and uses very little.


In other words I would not bother  



Trevor


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## Zebedee (Oct 3, 2007)

trevorf said:


> Gas is the most efficient method to run the fridge and uses very little. In other words I would not bother
> Trevor


Got a Gaslow bottle or two Mark?

Sounds like that would be a far more beneficial exercise. :wink:

Dave


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## gnscloz (Oct 4, 2008)

Zebedee said:


> Hi Mark
> 
> I'm trying to convince myself about solar panels, but it won't be easy on our van since there is so little available room on the roof. I would have to link several small ones, and scatter them around the flat (and still free) bits of the roof! 8O
> 
> ...


Hi Dave I was dead set against solar to start with thought with the b2b
Charger solved everything, but we don't use the van like we used too, we stay in one place a lot more now and don't always have hook up.
But now we have solar it's great, even on bad days your still getting some charge.
Your right I'll leave things as it is, there's me thinking I'd invented the wheel lol 
Mark 
Ps have gaslow, love that too


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## gnscloz (Oct 4, 2008)

trevorf said:


> On 12V your fridge will draw about 10 amps. Thats about your entire solar output in full sun at midday. Early or late in the day or when a cloud comes over you will be draining your leisure batteries.
> 
> The mains element in a fridge is around 600W. The 12V element only around 120W so much less efficient at cooling. They rely on increased air flow due the van moving ie engine running and travelling. Even then, no where near as much cooling as mains or gas.
> 
> ...


Hi Trevor thanks for the technical info,
Clearly that's why you can't do it, 
Think have too much time on my hands 
Mark


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## spatz1 (May 19, 2011)

you re on the right track as it is a lot of power to not make use of....

i hit 20a early morning before the solar regulator quickly winds it down and manage to run the 46 inch tv most of the day and his allowance of an hour a day on the xbox via the hook up cable revearsed with an extension socket on the end placed in the house...


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## Jezport (Jun 19, 2008)

gnscloz said:


> Hi we have swift sundance on x250 cab with dometic 3 way fridge,
> We now have 200 watts of solar and I'm sitting here trying to think of a way of utilising the spare electric, feeding 12 volts to fridge comes to mind, as anyone undertook the task, my handbook states 12 volts to fridge only works with engine running.
> Mark


Ive got 220w of solar panels plus 460AH of battery bank and it still wouldn't be worth considering running an absorption fridge on them.
Maybe worth it if you had a compressor fridge and plenty of sun.


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## pete4x4 (Dec 20, 2006)

Its not that daft an idea, most new fridges are around 170W and are thermostatically controlled on 12v now a days.
An automatic input selection fridge ought to be able to cope but I suspect you would need something that only connected 12v when you had that much available and used some sought of hysterisis to ensure that you hadn't lost 12v temporarily.
Reasonably easy to do but not sure of the market.


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## Jezport (Jun 19, 2008)

pete4x4 said:


> Its not that daft an idea, most new fridges are around 170W and are thermostatically controlled on 12v now a days.
> An automatic input selection fridge ought to be able to cope but I suspect you would need something that only connected 12v when you had that much available and used some sought of hysterisis to ensure that you hadn't lost 12v temporarily.
> Reasonably easy to do but not sure of the market.


Where your plan falls down is:

The 12v element will not keep the temperature low enough if the fridge is used i.e. door opened and closed a couple of times.

You would be using all your solar output and more if the weather was dull to run the fridge especially when you consider that solar output is best in bright sun and the fridge will struggle in bright sun.

Gas is efficient for the fridge and unless you have a compressor fridge.

We spend tens of thousands of pounds on a heavy overpriced van that gobbles diesel yet some feel the need to save pennies on gas!


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## gnscloz (Oct 4, 2008)

Jezport said:


> pete4x4 said:
> 
> 
> > Its not that daft an idea, most new fridges are around 170W and are thermostatically controlled on 12v now a days.
> ...


What the problem it's a forum people run ideas thru so people can disscuss not every one is a expert , clearly like yourself so we ask questions,
I have a bodyshop some of the ridiculous things I see on here make me smile but I give a sensible reply just like yourself on your first post,
I then don't follow on with sarcastic patronising comments about penny pinching.


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## Jezport (Jun 19, 2008)

gnscloz said:


> Jezport said:
> 
> 
> > pete4x4 said:
> ...


Not sarcasm, just an observation of a strange habit some motorhomers have.


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## pete4x4 (Dec 20, 2006)

Sometimes you have to stop being a dinosaur and look forward.
The idea of running the fridge off free 12v and supplementing it with gas is an environmentally sound idea and has been done elsewhere with other forms of energy.

As a point of discussion it can be done and it would be better than burning fossil fuels.
Certainly my new Dometic fridge runs perfectly happily on 12v and continues to freeze so gone are the days when fridges could not run normally on 12v.
So if you have 13A available from your solar panel you could run your fridge as if it was on gas and you would't notice the difference
.


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## crusader (Jul 5, 2012)

I too have had this thought , got 200w of solar 330 amp of battery and a sterling 1800 inverter and plan to " power" the van on 240v if only for a couple of hours in the summer, have done a trial run and it seems ok ( yes everything is fused and connected correctly :roll: ) it to me makes sence to use the power available but not at the risk of flat batteries , oh got gaslow aswell , jim


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## dpsuk999 (Mar 25, 2012)

I have the option to have my fridge running of my batteries (450ah) 6v Trojan batteries wired in series to give 12v.

Its ideal for when you are on the ferry or tunnel and cannot have gas on, it draws between 6 and 8 amps so theoretically i can run it off the batteries for 28 hours before iam at my 50% drain limit, but will also work if you have 120ah battery, can still run for approx 7.5 hours at 8amps before you get to the 50% drain limit.

When across the waters, driving for an hour for example will pump back into your batteries anything from between 100 and 150 amps from your alternator so all good


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## listerdiesel (Aug 3, 2012)

trevorf said:


> On 12V your fridge will draw about 10 amps. Thats about your entire solar output in full sun at midday. Early or late in the day or when a cloud comes over you will be draining your leisure batteries.
> 
> The mains element in a fridge is around 600W. The 12V element only around 120W so much less efficient at cooling. They rely on increased air flow due the van moving ie engine running and travelling. Even then, no where near as much cooling as mains or gas.
> 
> Trevor


Electrolux quote the following figures for the RM2267 fridge (as an example) Which is the one with the freezer compartment as well as the basic fridge:

Power input:

Gas 173 Watts (equivalent)
12V 100 Watts
230V 100 Watts

So around 8-10 amps on 12V, depending on your battery voltage.

As said, gas is the way to go, we've now got 320W of solar panels, but I'd still stay with gas as it is much more effective than 12V or mains.

Peter


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## VanFlair (Nov 21, 2009)

Hi

just to add my 2 pence worth. I have just fitted 3 more 80watt panels so now have 4 in total, the regulator for the three new ones is a Votronic MPP240 and when I read the spec I saw that it had the facility to switch a Dometic AES fridge onto 12volt when it saw that there was surplus solar power. As I had this feature I thought that I might as well try it out, you should connect the AES wire from the regulator to the S+ on the fridge BUT older fridges dont have this terminal only D+ to trigger 12volt operation from the alternator however if you wire straight to the D+ and put a schotky diode in the wire from the alternator to stop any flow through the alternator windings when the engine is not running it all works OK.

We have not had that much sun yet but if we leave the fridge on automatic we sometimes come back to it and it is running on 12volts, I dont know how long it will stay on 12volts for but may know more when we go to France and get some sun (hopefully) it might not stay on for long if the 12volt comes from the engine battery as all the solar goes to the leisure batteries and I am not sure how much the CBE put from leisure to engine. I know most people think it is not worth the bother but it all seems to work OK and it only cost a piece of light wire and a 69pence diode so I thought I would give it a go.

The other advantage is that I can post on here when somebody asks the question and it might even sound like I know what I am talking about (I dont). :lol: 

Martin


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