Looking to upgrade to two 6 volts. Can't fit a double box in the area my single 12 volt is. Would it be ok to locate one on one side of the camper and one on the other with the batteries wired in series appropriately. So there'd be 12" hot to the first, about 8' between the negative and positive of the 2 batteries, and then 8' return from the negative of the 2nd battery.And would be looking to put on portable solar.

You'll lose a little efficiency, but not much. This wouldn't be any worse than longer battery cables to the pair.Use as large of wire as possible and you'll be fine. I'd suggest a #4 if practical.

Sure you don't mean 4/0 ? There's a huge difference

Yes, there is a huge difference. I'm suggesting #4 because it's a practical wire diameter for commonly available connectors. 4/0 is about the size of your thumb and is not practical to work with. In a short run such as this there is not a significant difference in the resistance between the two.

Hiking Hunter wrote:Yes, there is a huge difference. I'm suggesting #4 because it's a practical wire diameter for commonly available connectors. 4/0 is about the size of your thumb and is not practical to work with. In a short run such as this there is not a significant difference in the resistance between the two.There is a five-fold difference between 4 AWG and 4/0 AWG, in resistance. I would recommend at least 2/0. If there is anyway to get the batteries closer together, I wouldn't locate them at a distance of 8'.

Recommending a wire size when you don't know the current is hit or miss. Yes, bigger is always better but if the OP can estimate his load he can then decide on a wire size that is going to work well for the application. In my bus I connect my batteries with 2/0 because I have an inverter that can pull some current, in my truck camper I use 6 gauge because the only thing I run is some lights so the charger is actually the highest current.Brian

7 feet between 6 volt batteries in series? | Good Sam Community

richardcoxid
Explorer
Jun 05, 2014
Here is a hint about battery cables/crimp on terminals.

Go to your local Welding Supply Store, they will have spools of various gages of welding cable. Have them cut the cables in the lengths that you want. Normally they will also have an assortment of crimp on terminals in various sizes.

Welding cable is MUCH more flexible than standard battery cables and has an industrial strength insulation. My local shop will even crimp on the terminals for me and normally will be less expensive than the pre-made cables at auto supply stores, plus they will be cut to your custom lengths.

Remember to measure the length twice and cut once!
rrwantr
Explorer
Jun 02, 2014
No built in gen. Believe wiring in there is #4
tenbear
Explorer
Jun 02, 2014
I would look at the OEM wires used on your battery and use the same size.

If you have a genny, it can draw a starting current of about 60A.
rrwantr
Explorer
Jun 02, 2014
Thanks for the info. Appreciate it.
Hiking_Hunter
Explorer
Jun 02, 2014
Sure, bigger is better, but let's be reasonable. If we follow the "bigger is better" rule to the letter, we would all be using buss bars between our batteries.

The resistance of a #4 conductor is .2485 ohms PER 1000 FT.
The resistance of a 4/0 conductor is .049 ohms PER 1000 FT.

The OP would be adding approx 14 ft of conductor (one pos, one neg) between his batteries. This is compared to an approx 1 ft. connection between batteries if they are side by side. Therefore, the total resistance of the added #4 conductors would be .003479 ohms and the total resistance of the added 4/0 conductors would be .000686 ohms.

A Trojan T-105 battery can deliver 225 amps for short periods, but that's not the typical current demand in a camper. A more typical draw would be 20 amps for the load the OP has described. So, at 20 amps...

The voltage drop across the #4 at 20 amps would be .06958 volts, and the drop across the 4/0 would be .01372 volts.

The difference between the #4 and the 4/0 cables, at a 20 amp discharge rate, would be .05586 volts, not a significant amount.

This would be the value for discharge. The immediate voltage difference for charging would be much lower since it is at a much lower current.

Lets be practical with the conductor size. The additional cost and difficulty of installation for a 4/0 cable is not worth the return.
rrwantr
Explorer
Jun 02, 2014
That's true. Forgot about that as I was typong that up. Lol
Bobbo
Explorer II
Jun 02, 2014
kaydeejay wrote:
Only thing I would do different would be to ground the second battery at its location, rather than have that 8' return lead.
Otherwise I'd say you're good to go.

+1 since it is just a frame ground anyway.
kaydeejay
Explorer
Jun 02, 2014
Only thing I would do different would be to ground the second battery at its location, rather than have that 8' return lead.
Otherwise I'd say you're good to go.
rrwantr
Explorer
Jun 02, 2014
The only thing I am using is some lights, furnace at times and tv.
VintageRacer
Explorer
Jun 02, 2014
Recommending a wire size when you don't know the current is hit or miss. Yes, bigger is always better but if the OP can estimate his load he can then decide on a wire size that is going to work well for the application. In my bus I connect my batteries with 2/0 because I have an inverter that can pull some current, in my truck camper I use 6 gauge because the only thing I run is some lights so the charger is actually the highest current.

Brian