This is just hypothetical, so I can learn something.If you had 15' of negative wire going to the battery, and 10' of positive wire... and there was 2 or 3' of slack in the shorter positive wire... would anything be gained by shortening it? It does come into play somewhat in my MH project due to the locations of shunts, terminals, and such. In reality my lengths are not that far off and I'm not likely to mess with things for minuscule gains. But I'm curious about the concept anyway.

For a 4 gauge wire there is less than 0.001 ohms of resistance per foot of wire. For 100 amps that would be less than 0.1 volt drop in that wire. Insignificant.

The pos and neg paths do not have to be the same length or gauge. The R on the circuit is the total of the R on the pos and the R on the neg pathsSo if you reduce the R on the pos path only that helps with the total R. It may or may not be "worth it."Lengths of these paths not to be confused with the lengths of the links between the batteries themselves for balance.

BFL13 is correct and when wiring is too short, future wiring configuration options may also be limited...

I have found having all the distribution points equal lengths really comes into play when charging the batteries. You want all of the charging currents to be the same as close as you can them.I used the 4-way BLUE SEA Battery switch and all of its stub connections are my tie points. So I cut all of my 4AWG cables to be the same lengths inside the battery like wiring paths...When I am charging I can use my clamp-on DC CURRENT meter and read pretty much the same DC CURRENT going into each battery.Roy Ken

So, and this is how I should have put the question to make it simple, one cable 15' and one cable 5' is the same as two cables equal at 10'?

Battery wiring resistance question | Good Sam Community

21 Replies

Harvey51
Explorer
Dec 09, 2014
Why not just measure the voltage drop across the 15 feet of wire? Divide by 3 to get the drop over each 5 feet of it - and the gain you would get if you cut 5 feet off. While you are measuring check the voltage drop across the connections, which might be greater than in the wires.
2oldman
Explorer II
Dec 03, 2014
tenbear wrote:

I think you used 30' in the wire length. r.
yes I did. Thanks.
jrnymn7
Explorer
Dec 02, 2014
o.k., thanks.
ken_white
Explorer
Dec 02, 2014
It would depend on where the (+) and (-) connections were made but most times in small battery banks the imbalance is so small its not worth worrying about.
tenbear
Explorer
Dec 02, 2014
jrnymn7 wrote:
BFL13 wrote:
The pos and neg paths do not have to be the same length or gauge. The R on the circuit is the total of the R on the pos and the R on the neg paths

So if you reduce the R on the pos path only that helps with the total R. It may or may not be "worth it."

Lengths of these paths not to be confused with the lengths of the links between the batteries themselves for balance.

Would there be an imbalance if four 6v's were wired in series/parallel, and the series wires were both the same length, and the parallel wires were the same length, but the parallel wires were shorter than the series wires?

Thanks.

No
jrnymn7
Explorer
Dec 02, 2014
BFL13 wrote:
The pos and neg paths do not have to be the same length or gauge. The R on the circuit is the total of the R on the pos and the R on the neg paths

So if you reduce the R on the pos path only that helps with the total R. It may or may not be "worth it."

Lengths of these paths not to be confused with the lengths of the links between the batteries themselves for balance.

Would there be an imbalance if four 6v's were wired in series/parallel, and the series wires were both the same length, and the parallel wires were the same length, but the parallel wires were shorter than the series wires?

Thanks.
time2roll
Nomad
Dec 02, 2014
Snowman9000 wrote:
the question to make it simple, one cable 15' and one cable 5' is the same as two cables equal at 10'?
Yes
tenbear
Explorer
Dec 02, 2014
2oldman wrote:
This is what calculator.net gives:
Voltage drop: 0.75
Voltage drop percentage: 5.24%
Voltage at the end: 13.55

That's a lot.

I think you used 30' in the wire length. Calculator.net assumes 2 wires so it calculates the drop for 30' out and 30' back, 60' of wire.

BTW, I used the same calculator.
wolfe10
Explorer
Dec 02, 2014
Correct-- it is total distance the electrons must travel from battery back to battery.

Unequal length is just fine.

Shorter gives less voltage drop. BUT, voltage drop is only significant at higher amp loads. Said another way, if you have 10 gauge wire and are running two 10 watt bulbs (so less than one amp each) voltage drop would be negligible. As amperage you draw goes up, so does voltage drop.
doughere
Explorer
Dec 02, 2014
Snowman9000 wrote:
So, and this is how I should have put the question to make it simple, one cable 15' and one cable 5' is the same as two cables equal at 10'?

Yes.