Battery Bank Interconnect Cable Sizing?

[Catamount]

I am planning to upgrade my house battery bank to a set of four 6-volt golf-cart batteries, but I'm not sure what size the interconnecting cables need to be....

The cables leading from the bank to the house are 6 AWG protected with an appropriate fuse...

[btrayfors]

I'd recommend size AWG 1/0 for interconnections. While one often sees much lighter cable, I found during an 18-month long battery testing study that the heavier cable for interconnections is preferable. Usually, we're only talking about a few feet of wire for the interconnections, so the cost of the larger cable shouldn't be a factor.

Also, depending on your house loads and the length of cabling, AWG6 sounds a little on the light side. You might tally up the loads expected on it and do the calculation for voltage drop.

Bill

[witzgall]

Just remember to run the positive supply lead from one end of the string, and the negative from the opposite end - don't being them off of the same battery!!!

Chris

[Mardav]

If you can use a solid brass bar (buss bar) this is the best (look at the Surrette Rolls battery web site for examples), if that is not practical, then the largest pure copper cable you can fit (0 would be good).

[daddle]

If the lead to the house panel and fuse is appropriately sized at #6 the the interconnect should be, at most, #6 as well. Anything else sounds like hocus-pocus, extra money, extra weight. I wouldn't use brass bars, too heavy and they will unintentionally become a structural part as the batteries move around...creating problems...I would think.

[Catamount]

daddle, I can think of three or four reasons for going with larger wire size inside the battery box than that of the wire leading away from the battery box.

One would be in case you ever want to upgrade the wiring outside the box. Another would be if you ever want to use the house bank to jump the engine starter battery. A third would be that you want to reduce the internal resistance of your battery bank as much as possible to supply the best voltage that you can. Finally, these wires are not fused and while you wouldn't expect currents larger than those drawn from the bank, if a cell ever shorts out or otherwise becomes unequal to those of the other batteries in the bank, there could be some high internal currents.

I agree with you though that, although the batteries should be secure inside the battery box, a flexible interconnection would be better than rigid bars. The box allows a bit of room for the batteries to expand and contract with temperature, etc..., so there is, literally, some wiggle room.

witzgall, that's my plan -- connect to the bank at opposite corners, as it were.

Bill, I've been through the calculation a few times, and I believe the #6 to be good. It's a simple boat, with not much more than a few lights and some sailing instruments to power

Thanks all for the input!

[GordMay]

Very well said, Catamount!

[daddle]

Neato...change the question AND toss out all engineering...typical forum procedure...

The upgrade issue is just silly.

Jumping from the bank, presumably with auto jumper cables, is a reasonable requirement. But what size is the engine? A few feet of #6 will make little difference with a small marine diesel.

Wanting tho reduce the resistance inside the battery box is reasonable. But by how much? The voltage difference between #6 and the ridiculous 1/0 is what? A handfull of millivolts? The unavoidable internal resistance of the battery is far greater.

The shorted cell problem is an issue. But in this setup #6 marine wire can handle the current without melting the insulation.

As always, keep all wires as short as practical.