Wiring Question

Submitted: Friday, Apr 07, 2006 at 23:19
ThreadID: 32664 Views:1761 Replies:7 FollowUps:3
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Ok Folks,

Here is the setup so far. I have a dual battery system in my Hilux. Cranker for starting and my aux battery is a deep cycle. I use a smart solenoid, surge protector and battery charge monitor on this setup as well. From the aux battery I have it cabled through to an Andersen plug at the rear which mates up to my camper trailer and charges the deep cycle battery in the camper while we are on the move.

Here's the bit I need some advice on. I carry two three way fridges in the back of the Hilux and need to get juice to both of them while we are on the move. Once I get where I am going I go onto gas so it is only the arrangements in the car I need some advice on. The fridges only have cigarette lighter style plugs on them so I guess these need to be changed as well.

What do you all advise is the best wiring configuration from the aux battery to the fridges?

Thanks in advance.
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Reply By: Member - Troll 81 (QLD) - Saturday, Apr 08, 2006 at 01:56

Saturday, Apr 08, 2006 at 01:56
If the wire going to the back is thick enough you can probably just tap into that?
AnswerID: 165729

Reply By: Member - Toolman (VIC) - Saturday, Apr 08, 2006 at 07:55

Saturday, Apr 08, 2006 at 07:55
I am just in the same process and have purchased a fuse box (8 fuse) which I will be connecting to the Aux battery via a reasonably thick wire. I'm running separate lines to wherever I need them. I also plan to run an earth wire from the Aux battery to a point inside the truck and from there to each power point just to be sure of a good connection.

AnswerID: 165755

Reply By: Darian (SA) - Saturday, Apr 08, 2006 at 08:31

Saturday, Apr 08, 2006 at 08:31
My situation is similar.....I'm charging a trailer while mobile too, via the heavy line and andersons. To get power for my fridge I tapped into the heavy trailer line at a convenient spot - could see no need to duplicate - when the trailer is off, that line feeds the fridge - when the trailer is on, it can happily supply both. Rewired the fridge connector to Hella plug - made a multi outlet box for the rear, to supply other appliances as well. My Waeco of course draws a lot less than current than your two 3-ways (they might total 17A ?) - still not an issue if set up properly I'd have thought.
AnswerID: 165759

Follow Up By: Member - Roachie (SA) - Saturday, Apr 08, 2006 at 08:59

Saturday, Apr 08, 2006 at 08:59
It's a good idea to tap into the wire that leads to the Anderson plug. That saves having to duplicate the wiring all the way from the Aux batt.

However, I reckon this extra wiring to the fridges would need to be pretty heavy gauge (say 8mm minimum) and I wonder whether you've thought about using these slightly smaller anderson plug type connectors as currently available in the Trader Section on this website? They are small than a normal Anderson plug but have the same excellent connecting qualities. The seller has a number of them for sale in red and black.

Get rid of the cigi plug IMHO


FollowupID: 420646

Reply By: Keith_A (Qld) - Saturday, Apr 08, 2006 at 09:00

Saturday, Apr 08, 2006 at 09:00
Hi Brian -
When wiring my unit, I used Collyn Rivers website and formulea to calculate the size of the wire. Here is the site : Site Link

If the wire size is large enough to the anderson plug, then tap into it.
If not, run a separate wire for the fridges (probably the best solution).

3 Way fridges use around 10 -15 amps. Lets say 15 maximim.
Now for Collyns forumlea :
The voltage drop from battery to unit should not be more than3%.
So for a 12V system = 12 x 3% = 0.36V
Voltage drop =
(length of wire) x (current draw) x .017 divided by wire cross sectional area in sq mm
So - if the total length from car battery to Fridges is say 6mtrs -
: 6m x 30amps x .017 div by wire sqmm = 0.36V
Wire cross sectional area needed = 9sq mm to run the fridges.

So - using cable with 10sqmm of COPPER will nicely suffice for just the fridges.

What of the camper battery?
Well that depends on the current draw to charge it.
If the camper battery only supplies lighting, water pump and maybe inverter for laptop etc, then it won't draw large currents - say 8 amps after a 5 day camp.
This will drop quickly as the battery recharges, so it is not linear.
I am unsure how to 'best guess' this figure - say 8 amps.
Total current if only one wire is used for both fridges and camper :
30 + 8 = 38 amps.
Total distance from car battery to camper battery - say 10 mtrs
Apply formulea :
10 mtrs x 38 amps x .017 div by wire sqm = 0.36V
Wire cross sectional area needed = 19 sqmm.
As you know, the full 38 amps are not travelling the full length of the wire.
Better a larger wire than blown fuses or burnt wire.
So, you have a choice : Run 20sqmm wire from the car battery to the camper, and tap into that for both fridges; or run say 6sqmm wire for the camper, and separate 10sqmm cable just for to fridges.
I would run a separate cable with separate cut-outs for the fridges.
Read Collyns web site, and note the issue re automotive cable size!!

What do I use : I run 16sqmm cable from the Aux to the camper. (Only 1 fridge.)
Also - I run both positive and negative all the way from battery to battery, with 30 amp cut-outs at both ends. Perhaps overkill, but it takes the same effort to install thick wire as thin wire, and the extra cost of materials is marginal.
Happy camping.........................Keith
AnswerID: 165764

Follow Up By: Pterosaur - Saturday, Apr 08, 2006 at 10:13

Saturday, Apr 08, 2006 at 10:13
Total length = distance from aux. battery to load (x2) - for 2 wires
FollowupID: 420659

Follow Up By: Member - Mike DID - Saturday, Apr 08, 2006 at 10:54

Saturday, Apr 08, 2006 at 10:54
So you will need to use AT LEAST 4 Ga cable - 21mmsq - 7mm diameter copper - 10m diameter over the insulation.

FollowupID: 420666

Reply By: Member - Phil G (SA) - Saturday, Apr 08, 2006 at 10:11

Saturday, Apr 08, 2006 at 10:11
Like the others said, two 3-way fridges will use a heap of power on 12 volts - minimum of 20amps continuous, so I'd suggest a minimum of 8gauge cable, which is what I use anyway.

And cig sockets won't hack it - I'd suggest the 50amp Anderson plugs.

I'd have a dedicated fuse to the fridges, and its worth having an indicator light or gauge to know they are working - those fridges are silent.

Also, some people slip a computer fan in there to help the 3-way fridges work in the back of a packed vehicle.

AnswerID: 165772

Reply By: Pterosaur - Saturday, Apr 08, 2006 at 10:17

Saturday, Apr 08, 2006 at 10:17
I ran two 40 litre electric fridges for a while off two batteries - had to drive on a daily basis to keep them both working (1 freezer).

The fridges were separately wired with 6mm. copper

AnswerID: 165774

Reply By: Brian B (QLD) - Saturday, Apr 08, 2006 at 20:15

Saturday, Apr 08, 2006 at 20:15
Thanks everyone for your ideas.

Cigi plugs will be gone and I will ensure the right cable size, fuses etc are used.

Have a good one.
AnswerID: 165851

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