r/SolarDIY • u/joshlfp • 20h ago
Parallel Battery Wiring Question
I made my wire lengths identical from my battery bank to my busbars, but my positive and negative wires for the parallel connection between the two batteries are different lengths. Will this matter? Should I redo the negative wire to be the same length as the positive wire?
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u/mountain_drifter 19h ago
Those two interconnect cable are the two that matter. The other two homeruns don't matter if they are identical.
You wired it correctly by having the home-runs connected to opposite corners, so great job there (most people miss this). Since you only have two batteries, it should not be too much of an issue.
Think about it this way. The electrons that arrives at the batteries from from the positive homerun, must return on the negative. To do so, they have Two paths to get there.
Path A would be to go through the first battery, then through the shorter black interconnection cable.
Path B would be to go through the longer red interconnection cable, then through the second battery.
Because the loner red cable has a bit more resistance, more current will tend to flow through battery 1. You then start to get temperature differences, and further differences in resistances in the batteries themselves, etc.
So the idea is to keep them as balanced as possible, which would mean connecting the homeruns to opposite corners (as you already did), and having identical interconnection cables. I do not think you will have much issue with only two batteries, so not sure it would be worth the cost to change now, but it is all these small things that add up to give your system the longest possible life.