(+) & (-) Parallel Cable Length with a BMS ??

[MrM1]

I am building two 8s packs each with its own 24v 100amp OverKill Solar BMS. I want to keep the main +/- cables between the packs and the busbars the same length. But the negative (-) will have the BMS in the middle so the negative cable will need to be split in two AND also will have double smaller wire. I Plan to use two 6awg cables coming off the battery negative to the BMS connection, and then two 6awg wire from the BMS to the negative Busbar. The Double 6awg should yield an effective 3awg wire size according to this Wire Combiner Calc

Here is What I do not know:
1. What wires size should I make the positive cable if the negative will be two 6awg cables? 3 awg or two 6 awg?
2. If my total length of the positive cable is 18", do I make the Negative 9"+9" ... OR ... do I need to compensate for the width of the BMS so the cables would be more like 7.5" + 7.5" + BMS of 3" = 18 (given the BMS would be about 3" wide) ?

Thanks
Mike

 

[Johncfii]

1. There is no significant difference between wiring the positive terminals with either a single wire, or with a pair of smaller wires having the same ampacity. There are subtle differences, such as needing twice the number of terminal lugs, and needing to maintain twice as many connections, but electrically, you should see no difference.

2. There is no reason to make to positive leads any longer than necessary. There is no electrical advantage to having positive and negative leads the same length. Adding lead length added only for that purpose will simply increase the voltage drop over the cable length, though that might be very small. But, if you just want things to look balanced, aesthetically, adding a bit of extra wire will not cause any significant problem either, as long as they are appropriately sized. Having the BMS inserted in the negative lead does not change this at all.

As you probably realize, you DO generally want to make the negatives leads to each pack all the same length, and the positive leads to each pack all the same length .... to help keep the two packs equally sharing the charge current and the load.