running fridge from car in carravan

Submitted: Wednesday, Mar 18, 2015 at 18:55
ThreadID: 117113 Views:2540 Replies:6 FollowUps:4
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Hello ...I want top run my 3 way fridge in my van while I travel while driving ..
I have a 2nd battery in the back of my ute which is charged by a 20 amp ctech charger.. so can I wire a vsr module from the 2nd battery then straight to the fridge or is it better to run to the 2 x 120 amp dc batteries in the van then to the fridge ..

cheers boxhd
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Reply By: scruffy - Wednesday, Mar 18, 2015 at 19:07

Wednesday, Mar 18, 2015 at 19:07
Personally, I would be charging the van batteries while driving and let the van batteries run the fridge as it does now. Less hassle all around. Bob
AnswerID: 551174

Reply By: oldtrack123 - Wednesday, Mar 18, 2015 at 19:39

Wednesday, Mar 18, 2015 at 19:39
HI
DO NOT RUN your 3way fridge from the van battery
That is saking for trouble!!!!
You could soon end up with flat van batterries, due to the fridg drawing current from them while they are not being charged
On top of THAt the fridge current will cause voltage drop which will make it almost impossible for the alternatror to charge the van battery
Best to run the fridge from the Aux in the ute via its own VSR or ignition controlled relay.

PeterQ
AnswerID: 551176

Reply By: Allan B (Member, SunCoast) - Wednesday, Mar 18, 2015 at 21:40

Wednesday, Mar 18, 2015 at 21:40
Considering the high current that a 3-way fridge draws when on 12 volt, you don't want it supplied from any battery.
It should be fed from the alternator (which happens to be connected to the cranking battery). So feed it from the +ve post of the cranking battery through a fuse and relay which is controlled by the ignition circuit. Then via an independant Anderson socket on the rear of the tow vehicle direct to the fridge. In this way, the fridge will draw current from the alternator but only whilst the engine is running thus preventing accidental discharge of your cranking battery.

Note that trying to supply the fridge from the circuit that charges your van battery will likely result in insufficient voltage being available for charging that battery.
Cheers
Allan

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AnswerID: 551182

Follow Up By: Nomadic Navara - Wednesday, Mar 18, 2015 at 22:19

Wednesday, Mar 18, 2015 at 22:19
Quote "So feed it from the +ve post of the cranking battery through a fuse and relay which is controlled by the ignition circuit."

That is the way Dometic recommend their MES fridges work. You can feed the fridge via an Anderson plug circuit or through large pins in your trailer connector (not the little ones like in the 7 pin flat connectors.)

If it is an AES fridge then take the heavy wire straight to the tugs battery and the sense wire through the trailer plug to the appropriate circuit in the tug. Read your fridges manual carefully to see how it is done.
PeterD
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Follow Up By: garrycol - Friday, Mar 20, 2015 at 11:33

Friday, Mar 20, 2015 at 11:33
It depends on the draw of the 3way - people need to know what the fridge draws on 12v - my 3 way draws 110W so 8-10amps depending on voltage.

So I happily have my 3 way connected via the camper battery to the car battery/alternator. In my case will take something like 15-20 hours to discharge the system.

Obviously a different fridge will have different usage.

But generally the claims that the fridge will drain the battery when travelling and parked is a bit sensationalist and if travelling will not normally be an issue - stopped overnight or camping is a different matter.

So know your 3way 12v usage and make judgements accordingly.

Garry
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FollowupID: 836733

Follow Up By: Nomadic Navara - Sunday, Mar 22, 2015 at 00:33

Sunday, Mar 22, 2015 at 00:33
Quote "But generally the claims that the fridge will drain the battery when travelling and parked is a bit sensationalist and if travelling will not normally be an issue - stopped overnight or camping is a different matter."

This is not being sensationalist at all. If your supply cable is as thick as your little finger all will be well. If you have the standard size used by van builders and auto electricians (6 mm auto cable) the fridge will drain your house battery. If you indeed have only 6 mm auto cable your fridge will be capable of being powered through pin 2 of the flat 7 pin connectors. How will it do so without burning the pin/socket? It will do so because the voltage loss will be so high that the current will be very low.

Many members attempt to run their fridge and charge their battery with 6 mm auto wire. If the voltage drop results in the fridge voltage being below 12.7 V (and vans with 'standard' wiring do) the battery will supply sufficient current to bring the fridge input voltage up to that voltage. It's only the switched on well informed who are not running into that trap.
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Reply By: Batt's - Friday, Mar 20, 2015 at 00:45

Friday, Mar 20, 2015 at 00:45
! use to have 2 batteries in my van charging off the alternator with the fridge running off them I think from memory they were 100 ah. If I was only pulling up for half an hour or less I would let the fridge run of the batteries without any problems eg fuelling up at a servo or ducking into a shop briefly. If I was pulling longer I would switch it over to gas easy done without any problems.
AnswerID: 551235

Reply By: patrolman2 - Saturday, Mar 21, 2015 at 17:02

Saturday, Mar 21, 2015 at 17:02
Hi,I run my waeco and fridge in the van from the deep cycle battery under the bonnet and the deep cycle battery in the van. I use a smart solenoid and both deep cycles are 100 amp/hr flooded batteries. If you start off with your fridges cold you would be only using around 10 amps all up.In saying that,your wiring must also be appropriate. 6mm auto to Waeco in truck and 6B&S through to the Van battery and fridge.Have been doing it for years successfully and always have all batteries in state of "high" charge. Go shopping,sightseeing or long lunch..fridges are always cold and the food in the freezer always solid.Don't forget you are drawing from 200amps and being topped up from the alternator…Cheers
AnswerID: 551346

Reply By: WBS - Sunday, Mar 22, 2015 at 09:17

Sunday, Mar 22, 2015 at 09:17
I always thought that at the time of manufacture as standard practice across the industry, the the caravan fridge was never connected to the caravan battery. At best, the caravan battery could be charged from the vehicle via an anderson plug. If you wanted to run the fridge then a special heavy duty cable was needed to run from the cranking battery to the caravan fridge via an Anderson plug. At least thats the way my caravans have been wired. I'm talking about 3 way fridges (absorption).

Both caravans I've owned were wired that way. Maybe things have changed since I last bought a caravan.

I have been considering fitting a DC-DC charger in the boot of the caravan to charge the van battery while on the road rather than using the cranking battery direct, An expensive alternative but probably more efficient from my investigations. I'm just not sure about what the relationship between the DC-DC charger and the 240 charger in the boot would be. Another question for another post.
Tom
AnswerID: 551372

Follow Up By: patrolman2 - Monday, Mar 23, 2015 at 14:58

Monday, Mar 23, 2015 at 14:58
Interesting WBS. My fridg is wired directly to a 100amp/hr sealed deep cycle battery through 6 B&S cable and fuse. The battery is charged from the vehicle through 6 B&S and via anderson plug. Your idea of a DC-DC charger is an excellent one and most likely a little more efficient and certainly a little more expensive at the setup stage. I am very pleased with my setup as there is minimal voltage drop from from front to fridge.
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