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Old 09-26-2021, 05:34 PM   #1
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Connecting batteries with equal length wires vs matched resistance.

Still working on planning our my inverter upgrade and moving to lithium. My plan is to use three 206ah SOK batteries and a Magnum MSH3012RV inverter.

It seems like there two schools of thought on how to wire the batteries together.

The most common approach seems to be to connect them all together in a line using 4/0 wire and then tapping the negative off the battery on one side and the positive from the other side.

The alternative approach is to have each battery connect to a terminal block using equal length wires. I guess those equal length wires could be smaller then 4/0. Maybe 2/0.

Is there any real compelling reason to go with equal length wires? And if so what are they?

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Old 09-26-2021, 10:33 PM   #2
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I like the buss bar method. Mainly for ease of installation/isolation if necessary.
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Old 09-27-2021, 07:38 AM   #3
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Ampacities of cables is dependent on both the insulation type and and the environment they will be operating in. That said, 4/0 cable should be good for at least 300 amps in most environments and 1/0 should be good for roughly 200 amps. 2/0 will be in between. Those are ball park, only.

If you choose to parallel them on a bus like NewBlackDak is suggesting, I'd go with the 4/0. That would give you a good and safe installation. If you go with a terminal block, the 2/0 should be plenty adequate. You would be talking about a lot more connectors and what I would think would be a bit of a cluttered installation using the terminal blocks. But it would surely work.

I would say that you should connect them in a manner that won't be overly difficult, and I wouldn't stress about cable lengths. Make it easy on yourself. Make it a "clean" installation. You'll be fine, either way. Whatever you do, remember that the installation of the lugs on the ends of the cables will be your most critical concern. Make sure that is done right!
Jim & Angie, Boise, ID
2021 Entegra Esteem 27U
2017 GMC Acadia Denali
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Old 09-27-2021, 08:40 AM   #4
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i only have two batteries but i went with the bus bar technique. both of my batteries are in their own sealed and vented battery box. there is a small opening on each side of the box to allow a battery cable in. if i had connected the two batteries together using jumper cables between the two batteries i would have had to allow for three cables to exit each box (a positive on one, a negative on the other, and two jumpers on each). by using a bus bar on the outside of the boxes on each side i only have to run a positive and negative cable out each box and i can use the existing cable openings. i don't need to route jumper cables between the two batteries. the factory installed jumpers were 4 gauge cables. i used 1 gauge for the cables from the battery terminals to the bus bars. that was the biggest that the local auto parts store that made the cables had.
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