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In parallel battery banks, do the cables have to have the same lengths on each side?

jdege

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Dec 16, 2020
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175
The standard advice when wiring batteries into a parallel bank is that the cables all have the same lengths.

But is this in total, or on each side?

Suppose I have four batteries that I'm wiring in parallel. I have a positive bus bar and a negative bus bar. I have a cable running from the positive terminal of each battery to the positive bus bar, a cable from each negative terminal to the negative bus bar, and I attach my loads to these bus bars.

The recommendation is that all of the cables connecting terminal to the bars be the same lengths, but that clearly overgeneralizes things. If, for example, all of the positive cables were one foot long and all of the negative cables were two feet long, there'd still be equal voltage drop across all batteries.

But suppose the differences weren't the same for each polarity? Suppose I had two batteries with 1' positive cables and 2' negative, and two batteries with 2' positive and 1' negative. Every battery had 3' of cable in total, but some had a longer one the positive and some on the negative. From what I can see this would still result in the same voltage drop for each battery, and thus equal loads.

Given the physical layout of my battery installation, I'd have a cleaner install, were I to do this sort of asymmetrical installation.

Am I misunderstanding anything?
 
It is in total. The idea being, you want each battery to have the same resistance through the wiring and connections.

It is easy to keep track if you make all positives for each battery the same, and all negatives for each battery the same. But nothing wrong with different lengths if they all add up to the same length in total. Make sure you also use the same fuses and fuse holders, switches, etc for each battery.
 
And use on-ox-id special A on all the contact surfaces to prevent corrosion and make for a better connection.

I suggest you measure things and then cut all the cables laid out so you can get the length as close as possible before crimping
 
Make sure you also use the same fuses and fuse holders, switches, etc for each battery.
I'm thinking a class-T on the positive post of each battery, and nothing much else within the bank.

The monitor
And use on-ox-id special A on all the contact surfaces to prevent corrosion and make for a better connection.
What makes NO-OX-ID superior to the dielectric grease I already have?
I suggest you measure things and then cut all the cables laid out so you can get the length as close as possible before crimping
I'm having the cables professionally made.
 
You can lookup and read the description, it claims to cut through the aliminum oxide layer like is used on battery terminals.. I prefer it to others, as do a lot of others here. But you can use any you like.
 

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