Cable Size to charge Camper Battery

Submitted: Saturday, Jul 10, 2004 at 21:14
ThreadID: 14546 Views:6047 Replies:6 FollowUps:5
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I have been looking through the posts to try and sort out what cable size I need to charge a Deep cycle campertrailer battery. It seems that there is no consensus with some people using 5mm and anything up to 25mm cables that I have read about. Currently I have a 7mm cable but I am told that I really should have about a 10mm cable minimum. I gather that you can use one of those Attic twin battery chargers to compensate for any voltage drop in the cable.

What are people finding successful and is 7mm going to be enough?

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Reply By: Eric Experience. - Saturday, Jul 10, 2004 at 21:54

Saturday, Jul 10, 2004 at 21:54
For a balance between safety and satisfactory charging a total resistance of about .1ohm is best, this includes the resistance of all components, ie the wire, the relay, the cct breaker, any plugs or connections. The reason it is best not to use very heavy wire is to limit the current to a managable amount if you get a short due to a wire being pinched in the tow bar or coupling. To establish the best wire size you first must determine the length and then calculate the wire size. You do not reqiure any fancy black boxes to make the system work. Eric.
AnswerID: 67269

Follow Up By: Lone Wolf - Saturday, Jul 10, 2004 at 21:58

Saturday, Jul 10, 2004 at 21:58
Gee, I'm glad he said that, cause now I can seem all intelligent and say......."... I was going to say that!!..."

Mate, I wouldn't have a clue!!


Dumb ( & bored ) Wolf
FollowupID: 327987

Follow Up By: phil - Sunday, Jul 11, 2004 at 10:40

Sunday, Jul 11, 2004 at 10:40
0.1 ohm is too much. Think about it, it means a voltage drop of 1.0volt at 10 amp charge. This means that you will only get a very low charging rate since the battery needs at least 13.5 volt to achieve a reasonable level of charge.
Phil I
FollowupID: 328013

Reply By: mr diamond - Saturday, Jul 10, 2004 at 21:55

Saturday, Jul 10, 2004 at 21:55
gday kidz.
since we mounted the weaco in the camper we run 6mmx2 no problems at all.
reason for 6mm x2 im to bloody miserable to bye bigger cable .lolol
6mm cable not even $1 per metre
AnswerID: 67270

Reply By: Member - Geoff & Karen - Saturday, Jul 10, 2004 at 22:47

Saturday, Jul 10, 2004 at 22:47
Hey, have you got a new camper trailer or is the the one you had........
AnswerID: 67277

Follow Up By: Big Kidz (Andrew & Jen) - Monday, Jul 12, 2004 at 07:22

Monday, Jul 12, 2004 at 07:22
No new camper!! I had quickly wired in a cable to try and charge the battery of the one that we had while staying in Birdsville. Not sure whether I should try and mount it permanently for when the time comes or pull it out and upgrade it.

FollowupID: 328115

Reply By: Member - Captain (WA) - Saturday, Jul 10, 2004 at 23:16

Saturday, Jul 10, 2004 at 23:16
Hi Big Kidz,

The bigger the cable the better as you will get a voltage drop by the time the current finally gets to your camper trailer. As an example, a 0.1 ohm total circuit resistance will result in a voltage drop of 1.5 volts at 15 amps (typical recharge current draw). An alternator nominally puts out ~13.8V, so you are now down to 12.3V at the van battery. This will never fully recharge your battery.

As you mentioned, an Arrid Twin charge boosts the voltage back up to ~13.8V and enables a 100% recharge of the van battery. But it will also take some time as deep cycle batteries recharge relatively slowly.

Also, you should ALWAYS fuse any cable, no matter what size it is, as close to the (vehicle) battery as possible AND at the van battery end as well. The reason for the "double fuse" is that if the cable is pinched at say the drawbar, power can come from either battery and potentially start a fire. If you use a small cable to limit current draw, all you are doing is using that cable as the fuse!

Personally, I run a 3 stage "smart" charger on my van battery and simply use 10mm2 cables from my Patrol to keep my van battery ~80% charged while away from 240V. But if you are away from 240V for extended time periods, an Arrid twin charge (if on the move daily) or solar (extended bush stays) is the way to go IMHO.


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AnswerID: 67281

Reply By: Magnus - Saturday, Jul 10, 2004 at 23:46

Saturday, Jul 10, 2004 at 23:46
Hi Big Kidz,

Like Captain I use a 3 stage charger for my deep cycle camper trailer battery and a solar panel to top up,

As it is a deep cycle I don't even bother to try to keep it charged via the car system when on the move. Don't want to complicate life too much and set up with the Arrid gear.

Rely on 240 and the 3 stage charger or the solar panel when camped.

I use gas fridge so no large draws.


AnswerID: 67282

Reply By: Member - PatC - Sunday, Jul 11, 2004 at 18:01

Sunday, Jul 11, 2004 at 18:01
Hi Big Kidz
I've run a 6mm cable through an Anderson plug. I get 13.5v at the battery in the camper. It's been like that for 2 years and I've never had a problem or a flat battery but I'm not running a fridge of it though I believe I could if I wanted to. I just run lights and stuff.

See Ya
AnswerID: 67340

Follow Up By: Member - Roachie SA- Monday, Jul 12, 2004 at 20:29

Monday, Jul 12, 2004 at 20:29
I'm with you...6mm should be adequate


Andrew, this would relate (IMHO) to the charging of a heavy duty battery as opposed to a deep cycler. I've said it b4 and I'll say it again; d/c's are only good for motorised wheelchairs, scooters/go-fors etc. They are designed to be very slowly and constantly discharged (same as in a camper trailer I hear you say), but THEN be plugged into a dedicated power supply overnight and topped up ready to do exactly the same thing the next day. IMHO they do not get enough charge from a vehicle's alternator even if the batt is under the bonnet, let alone when it is 5 to 6 meters away. They also are not built to take the kind of nasty vibrations experienced on our lovely corrogated roads and can shake themselves to bits inside.
I actually use an exide orbital in my camper at present. It's too bloody expensive and I must have had a rush of blood to the head when i bought it, but it is performing well.
Good luck mate
FollowupID: 328201

Follow Up By: Member - PatC - Tuesday, Jul 13, 2004 at 22:31

Tuesday, Jul 13, 2004 at 22:31
To true Roachie,
Sorry I should have said I'm not running deep cycle batteries. I run Bosch N70Z's and I never run them down to less than 10.5v.

See Ya
FollowupID: 328384

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