Dual Battery Setup - Can I connect fridge and aux battery to Isolator?

Submitted: Wednesday, Apr 28, 2010 at 23:15
ThreadID: 78065 Views:6112 Replies:3 FollowUps:8
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Hi there.

Just found these forums and have gather some great info.

I just have a question regarding the dual battery setup I'm planning between my hilux and camper.

I plan to have the aux. battery located in my camper, connected to the main battery via anderson plugs and an electonic isolator. My fridge (yet to buy but will probably be a 3-way), will be located in hilux while travelling.

My question is, what's the best way to connect the fridge whilst traveling? Is it best to make a connection direct to main battery, via isolator, or just have a separate relay from the main battery?
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Reply By: Battery Value Pty Ltd - Thursday, Apr 29, 2010 at 00:15

Thursday, Apr 29, 2010 at 00:15
Hello Mickos1,

I'm not a fridge man, but have heard from others that they can be power hungry. More power hungry than compressor versions.
So if you're planning on running the fridge off the second battery while stationary (in case no gas or mains power available) you have to spend big on deep cycle batteries, and means of properly charging them.

To your relay question, I don't see a reason why you'd want an additional relay - the isolation solenoid switch will do it all for you.

Best regards, Peter
AnswerID: 414644

Reply By: ABR - SIDEWINDER - Thursday, Apr 29, 2010 at 07:03

Thursday, Apr 29, 2010 at 07:03
Hello Mickos1

Run the 3 way fridge off an ignition activated relay on its own heavy cable.

Do not try charge an aux battery and run a 3 way fridge off the same cable as the battery will not charge properly and you will have less power in the battery then when you left home.

Unless your alternator is producing a constant 13.8+ volts and the cable is very heavy approx 25mm2 it will not work.

Regards

Derek from ABR
AnswerID: 414646

Follow Up By: Ianw - Thursday, Apr 29, 2010 at 19:16

Thursday, Apr 29, 2010 at 19:16
Derek, you are saying that the system that most people with caravans have will not work !!

Ian
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Follow Up By: oldtrack123 - Thursday, Apr 29, 2010 at 20:54

Thursday, Apr 29, 2010 at 20:54
Hi Ian
Obviously does not work ,as shown by number of posts perpetuating the MYTH that 3ways are no good on 12v
Derek's posts is correct, run separate heavy cables for fridge back to tug battery with an ignition controlled relay in circuit to disconnect fridge when engine is turned "Off'
Running of van battery en creases problem of van battery receiving max possible charge ,due to voltage drop in long undersized cables
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FollowupID: 684942

Follow Up By: Ianw - Thursday, Apr 29, 2010 at 23:32

Thursday, Apr 29, 2010 at 23:32
Mine seems to work OK, but then I have 25mm2 cable x 2 from car batt to caravan. Not a lot of voltage drop there !!

Ian
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FollowupID: 684962

Reply By: Ozhumvee - Thursday, Apr 29, 2010 at 09:23

Thursday, Apr 29, 2010 at 09:23
Direct connection to the battery is the only way to go with a three way frig.
As they need lots of power a system to turn it on only when the vehicle is running is needed as well.
The 12v section of a threeway frig is purely to maintain (which most can't they slowly defrost) frig temps while mobile. They will rapidly flatten the battery if left connected for any period of time.
Peter
1996 Oka Motorhome

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AnswerID: 414668

Follow Up By: oldtrack123 - Thursday, Apr 29, 2010 at 14:02

Thursday, Apr 29, 2010 at 14:02
Ozhumvee replied:
"The 12v section of a threeway frig is purely to maintain (which most can't they slowly defrost) frig temps while mobile.
Peter "

Hi
So that Myth cotinues to be perpetuated.

A 3way fridge usually has the same size [watts]element for both 12v & 240 v
Same heat input, works the same on both!!

The major problem with 12v operation is that THE FRIDGE IS NOT GETTING 12V @ it's terminals DUE TO UNDERSIZED WIRING
The other problem is that few are correctly installed [ventilation ,draught to cool etc}
Many , many threads on the sublject.

If both ares done correctly then they will not only maintain freeze but can actually cool down further if thermo is changed to lower temp
But do not use them without engine running or having ignition controlled relay fitted,will flatten bat very quick
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Follow Up By: Ozhumvee - Thursday, Apr 29, 2010 at 14:27

Thursday, Apr 29, 2010 at 14:27
Yes that is true about the wiring and most caravans and campers have inadequate wiring from assembly to run the frig on 12v effectively.
The only time I ever got the ones I had (bin type and van frig) was to connect them to the battery direct with jumper leads, even then if the ambient was over 25 deg C (which it probably would be in a closed van or camper with a frig heating the air) the 3 ways struggle.
It is much easier to get 240v to the frig than a "proper" 12v supply hence the fact that they usually work much better on 240 than 12v despite the elements being the same size.
The later model van frigs with better design and insulation do work ok on 12v even in the tropics but you had better have plenty of 12v supply to keep them going.
Peter
1996 Oka Motorhome

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Follow Up By: Ianw - Thursday, Apr 29, 2010 at 19:19

Thursday, Apr 29, 2010 at 19:19
Our fridge in the van has a 125w 12v element, but has a 175w 240volt element. 12v works fine up to about 30c. Will even freeze ! (with fans).

Ian
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Follow Up By: Mickos1 - Friday, Apr 30, 2010 at 08:26

Friday, Apr 30, 2010 at 08:26
Thanks guys, I think I'll go with the direct battery connection and ignition relay as recommended by most.

Cheers
Mickos
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Follow Up By: Maîneÿ . . .- Friday, Apr 30, 2010 at 08:46

Friday, Apr 30, 2010 at 08:46
Mickos1,
remember when using an "ignition activated relay", only when the car is running will the fridge be running, a simple on/off inline switch will give you more control over the fridge run time, but yes, you will still have to remember to turn the fridge onto gas, and off 12v at the same time.

Maîneÿ . . .
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