Battery distance and what gauge wiring is best?

[VocalVirgo]

I just commented on someone else’s post telling them my situation, which is similar to theirs, and I realized I may want to start my own thread asking you guys to get some better insight on the matter.

I have a bank of 7 batteries (deep cycle lead acid, Walmart brand)- 4 on the passenger side rear, placed shoulder to shoulder around the wheel well, under the bed. And then I have 3 on the driver’s side, shoulder to shoulder around that wheel well (the 3 + 4 are directly across from one another). They are as far apart as the van is wide. We are using 7’ of 6 gauge wire to connect the 3 on one side to the 4 on the other side of the van. The batteries aren’t charging quite right, and we think either the smaller gauge wiring and/or the distance between the 3 & the 4 batteries may be the problem.

So question: Would upgrading the wiring between the 2 sets (the 3 + 4) to 2 gauge solve the problem of having the batteries far apart from one another? And would it help if we also upgraded the wiring to/from all battery terminals to 2 gauge? Does a bank of more than a few batteries perform better with larger wires? Do the batteries not perform as well if they are far apart from one another, regardless of what size wiring we use?
I know that’s a few questions, sorry. But I feel like 1 or all of my questions/issues may be solved by keeping all 7 batteries together? Or maybe I can keep them where they are and just upgrade the wiring to 2 gauge. I don’t know. So I’m asking you awesome people for help .
Thanks so much.

[markopolo]

6 gauge wire is small for that job. Depending on length, it is often used in installations of up to 50A current with 50A fusing for protection.

00 gauge wire might not be much more expensive than the proposed 2 gauge.

Assuming 100Ah batteries and charging at 0.2C (20A) x 7 batteries = 140A It would take a very long time to fully charge a 700Ah lead acid battery bank even if using a high output charger.

You have to really do the wiring well to try to equal out the charging and discharging so that all batteries are used somewhat equally. This link explains it: SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

[booster]

I commented on the other thread, but it all comes down to how much difference there is between the resistance to each of the batteries and the charger or use points. A 5' difference can mess up the charge and discharge balance for sure, as I have had that, and you need to add up the positive and negative cables so differences build up quickly. Of course all the batteries should be the same manufacturer, model and size, age, and even from the same production run if possible.


I don't think there is a really big deal with the batteries being 5' apart if the cables lengths are matched and properly sized. The only real difference will possible temperature differences I think, which may or may not be enough to cause issues.


Even slightly undersized, for voltage drop, not heat, wiring can be OK but not great as it won't cause bad charging if the cables are balanced well. What the voltage drop will do is give low charge voltage at the high rate areas of the charging, but it will be on setpoint at the more important finishing areas as current drops. Inverters will also see lower voltage at high rates, which could cause low voltage trips or the inability to use as low a SOC battery. Of course proper or even larger wiring is always best.

[VocalVirgo]

Originally Posted by booster

I commented on the other thread, but it all comes down to how much difference there is between the resistance to each of the batteries and the charger or use points. A 5' difference can mess up the charge and discharge balance for sure, as I have had that, and you need to add up the positive and negative cables so differences build up quickly. Of course all the batteries should be the same manufacturer, model and size, age, and even from the same production run if possible.


I don't think there is a really big deal with the batteries being 5' apart if the cables lengths are matched and properly sized. The only real difference will possible temperature differences I think, which may or may not be enough to cause issues.


Even slightly undersized, for voltage drop, not heat, wiring can be OK but not great as it won't cause bad charging if the cables are balanced well. What the voltage drop will do is give low charge voltage at the high rate areas of the charging, but it will be on setpoint at the more important finishing areas as current drops. Inverters will also see lower voltage at high rates, which could cause low voltage trips or the inability to use as low a SOC battery. Of course proper or even larger wiring is always best.

Thank you, and to everyone who commented with advice and info.
Just after reading these, and talking to a friend who has a solar farm... I moved all 7 batteries together (#1 is no more than 3 feet from #7, we did some clever arranging) and rewired all the batteries with 2 gauge wire. Now, everything is fine. I will definitely replace these with Gel or Lithium batteries when these are done... But for now, It's all good.

THANK YOU, everyone!