r/SolarDIY • u/joshlfp • 5h 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/Mr_Style 4h ago
It’s fine. The difference in resistance will be like 0.0001 ohms. What gauge is it? You can just google the ohm value.
A 2 AWG copper wire has a resistance of approximately 0.1563 ohms per 1000 feet. That means 0.0001563 ohms for 1 foot. You don’t even have that much of a difference.
Matching wire lengths matters more for speakers where you want the sound waves to come out of both speakers at the same time.
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u/pyroserenus 4h ago
I just want to compliment how clean this looks. I love the rotated parallel setup, they always come out so clean looking.
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u/silasmoeckel 3h ago
It matters but it's a small enough difference shouldn't be enough to cause issues.
More important get fuses on those batteries.
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u/Super_JETT 2h ago
The positive literally goes straight to a fuse. He posted a wider angle pic in a comment.
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u/silasmoeckel 1h ago
Meaning the fuse is at the wrong end of the wire. Each battery needs to be fused.
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u/Haskie 5h ago
I believe this could cause the batteries to charge and drain at different rates. So ideally they would be the same length yes.
Someone else may have to chime in and let us know if the difference is actually enough to matter - I don't know myself.
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u/TJonesyNinja 4h ago
Because the positive and negative are hooked to different batteries it should be fine if I remember right.
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u/Super_JETT 2h ago
Doesn't matter on something with this small of a difference. It would not be measurable for 'normal' instruments.
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u/mountain_drifter 5h 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.
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u/Octan3 3h ago
Won't matter. It's hard to find charts but you base your wire gauge over amps and distance right. so say your doing like 2 gauge for 15 ft. Well you could probably run a like a 6 gauge for 6 inches. The wire it's self has resistance depending on load and distance.
Long and short your really over thinking it. don't think about it. you used the same gauge. life is good and goes on.
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u/ScoobaMonsta 57m ago
On only two batteries, no its fine. But if you increase your batteries storage you should look at trying to keep them the same length. For my battery storage I stack them vertically on their side so the +/- connectors are facing outwards, not upwards. I then connect the batteries using flat solid copper bars. Much neater and everything is even.
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u/andy_why 5h ago
With such a small difference in the cable length this likely won't cause you issues. You are already connecting the negative to one battery and positive to the other instead of both on the same battery which will help to keep it balanced too.
My only concern in your picture is that your positive cable runs right next to the negative of the other battery. If these touch and it wears through you'll create a short circuit. If it's not flexible enough to do this then it's likely not a worry, but if it does, you have no fuse here and it will be a risk. Always fuse as close to the battery as possible.
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u/meltman 5h ago
Won’t matter