Running a fridge on 12v or 240v

Submitted: Saturday, Feb 28, 2015 at 10:26
ThreadID: 111270 Views:3023 Replies:8 FollowUps:10
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My brother just purchased a 210 ltr fridge for his motorhome.It is a compressor fridge that runs on 12v or 240v.His mate who is an auto elec and is going to fit it said just wire it up for 12v because when you are plugged into 240v you are charging your batteries anyway so there is no advantage in wiring it both ways.He then said most modern caravans are wired up for 12v because the charger does the rest.Does the fridge run any better on 240v if not why wire it for both?Thanks all
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Reply By: Tony C16 - Saturday, Feb 28, 2015 at 10:43

Saturday, Feb 28, 2015 at 10:43
Depends how long you want to camp away from power.

If I was you I would connect both the 12 volt and 240 volt unless you have plenty of solar and at least 2 x 105 amp hour batteries.
AnswerID: 546715

Reply By: Member - Stuart and Gunny - Saturday, Feb 28, 2015 at 11:05

Saturday, Feb 28, 2015 at 11:05
One thing i was just pondering is with a 12v ,240v fridge does it have an inverter built in changing 12v to 240v or a transformer changing 240v down to 12v?Thanks all
AnswerID: 546716

Follow Up By: oldtrack123 - Saturday, Feb 28, 2015 at 23:21

Saturday, Feb 28, 2015 at 23:21
Hi
[Quote]
Member - Stuart and Gunny

One thing i was just pondering is with a 12v ,240v fridge does it have an inverter built in changing 12v to 240v or a transformer changing 240v down to 12v?Thanks all[end quote]

If it is a 3way Dometic fridge [absorption fridge] it simply hasTWO seperate heating elements [one for 12V the other for 240V]
Selected either manually or auto depending on model

If a 2WAY compressor fridge it will depend on BRAND.
Some simple versions consist of a transformer & a form of inverter
others do it all electronically

PeterQ
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Reply By: Frank P (NSW) - Saturday, Feb 28, 2015 at 11:17

Saturday, Feb 28, 2015 at 11:17
It's always better to charge an unloaded battery, especially to get the best out of a smart charger. That way, when the charger is trying to sense the battery voltage, it is not influenced by battery voltages being altered by applied loads.

So I would get the 240V wiring done.

Cheers
FrankP

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AnswerID: 546717

Reply By: mike39 - Saturday, Feb 28, 2015 at 11:28

Saturday, Feb 28, 2015 at 11:28
I think most of these new units have a 12/240 detect system whereby whilst travelling or parked it will operate on 12v., then when you connect to external 240v. power it automatically changes from 12v. to 240v.
If this is in the case of yours it should have a 240v. lead you simply plug into the 240v. outlet placed for a fridge connect and a dedicated high current 12v. supply to the appropriate terminals.
mike
AnswerID: 546719

Reply By: Member - Ross N (NSW) - Saturday, Feb 28, 2015 at 11:56

Saturday, Feb 28, 2015 at 11:56
My two cents worth.
I would go for wiring both as, say you arrive at a 240 source of power (eg Caravan park)
or you run a generator, you will charge your batteries much faster if the fridge load is not
on your batteries at that time
AnswerID: 546721

Follow Up By: Bigfish - Saturday, Feb 28, 2015 at 14:07

Saturday, Feb 28, 2015 at 14:07
+1..Also you never know when a battery could collapse or you are stuck someplace and have 240v available. You will find that the fridge will run colder and quicker to freeze on 240.
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Follow Up By: Member - Scott M (NSW) - Saturday, Feb 28, 2015 at 15:05

Saturday, Feb 28, 2015 at 15:05
+2 - use 240v when available .... more times you cycle the battery the lesser life - PeterD is spot on below...
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Follow Up By: Roachie.kadina.sa.au - Saturday, Feb 28, 2015 at 21:19

Saturday, Feb 28, 2015 at 21:19
+3. That is what I've done in both my Ultimate Camper trailer and my last 3 vehicles.

Roachie
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Reply By: Nomadic Navara - Saturday, Feb 28, 2015 at 14:13

Saturday, Feb 28, 2015 at 14:13
Your mate does not seem to know how most 240 V chargers (and for that matter solar controllers) work. As multi stage chargers go through their cycle they detect that the battery is fully charged by the reduction of current whilst they are in the absorption stage. When they are in the absorption stage they are producing a constant voltage. During this time the charge current drops down to 10 to 20% of their rated maximum current output. When the charger detects that the current has dropped that low they switch to float or maintenance charge.

However when you put a load on the battery the charger will attempt to supply that current. The internal circuitry of the charger detects that the current is greater than the current where it switches to float charge. It then switches back to the absorption stage. This in turn raises the system voltage to a value that is not conducive to long battery life. If you have the fridge wired only to the battery then the battery will be receiving a charge voltage instead of a float voltage when your fridge is working. If you connect the fridge to the mains power when it is available then your battery will not be subject to this continual overcharge when the fridg motor is operating.
PeterD
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AnswerID: 546726

Reply By: Member - Boobook - Saturday, Feb 28, 2015 at 15:10

Saturday, Feb 28, 2015 at 15:10
+ 1 for the 240V, but for a different reason.

If your fridge uses up to say 5A and an average of 1A then you can subtract that from the charger capacity. It you have a 25A charger then not much of an issue. But if you have a 10 charger then you lose charging capacity. The charger will suffer, the power station won't.

I don't believe having the fridge connected to the battery while charging. They cycle on and off and the off time is more than enough for any charger to see that the battery is charged. Though if you have a small capacity charger you lose every way.
AnswerID: 546731

Reply By: oldtrack123 - Saturday, Feb 28, 2015 at 23:12

Saturday, Feb 28, 2015 at 23:12
HI
As usual , You will get more relevent ANSWERS ,if you post the fridge brand & model Number
Like oils ,all fridges are not the same!!
Most 3way ridges have a higher rated element on 240V
So THEY WILL COOL BETTER & FASTER on 240V

Large 3way fridges can have a high wattage 12V element ,some even 275W that means 23A being taken from you battery /charger just for the fridge

PeterD has made THAT point & the possible consequences

3way fridges are not intended to be used from the van battery
THey SHOULD be connected to the vehicle with their own independent heavy cables
[Size will depend on run length & fridge 12V wattage]
They also require some form of isolation from the car battery when the engine is not running.,
Some models have THAT function built in ,so again MODEL number & BRAND is important!

PeterQ
AnswerID: 546749

Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 28, 2015 at 23:54

Saturday, Feb 28, 2015 at 23:54
Peter,

The very first line of the opening post says...."It is a COMPRESSOR fridge that runs on 12v or 240v."
It is not a 3-way.
Cheers
Allan

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Follow Up By: Member - Stuart and Gunny - Saturday, Feb 28, 2015 at 23:54

Saturday, Feb 28, 2015 at 23:54
Hi Oldtrack
The fridge is a compressor fridge which means it is not 3 way.12v or 240v only,so you have miss read my post.Thanks
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FollowupID: 834535

Follow Up By: oldtrack123 - Sunday, Mar 01, 2015 at 00:22

Sunday, Mar 01, 2015 at 00:22
Hi Ooops
Old age must be catching up

PeterQ
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FollowupID: 834538

Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 01, 2015 at 08:44

Sunday, Mar 01, 2015 at 08:44
Haha Peter..... On all of us!
Cheers
Allan

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Follow Up By: malken - Sunday, Mar 01, 2015 at 17:36

Sunday, Mar 01, 2015 at 17:36
My last van had a 160 litre 12v fridge which had some sort of thingy to the 240v plug which detected what power supply I was connected to. When driving and/or camped the fridge operated on 12v but if I plugged into 240v it detected that and used that power supply.
Cheers
Mal
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FollowupID: 834582

Follow Up By: oldtrack123 - Sunday, Mar 01, 2015 at 22:50

Sunday, Mar 01, 2015 at 22:50
HI Mal
The thingy is a relay that does the necessary change overs
IT is located in the fridge electrics

PeterQ
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