Battery wiring

[On The Fly]

Good day,

Statement: with a multi battery system in parallel all battery connecting cables need to be the same length. But what If, you cluster three batteries with the same length cable and the fourth battery is farther away with a cable that is 12 inches longer than the first three batteries.
My question, why is this a problem?
Using lithium batteries what is the actual “measurable impact” to your inverter performance and battery life. I know next to nothing about batteries, but they have BMS and a half-life that states that I’ll be dead when they hit 80 % of their life. Why not just make all the cables 12 inches longer. Or just forget about it and wire the fourth battery with a different length cable. Maybe the engineers can help.

[Country Campers]

I am not much help with this but only to suggest using a larger gauge wire for the longer run, this may offset the issue if there is one. I struggle with all of this as well so you are not alone.

Brian

[Yoda]

Good day,

Statement: with a multi battery system in parallel all battery connecting cables need to be the same length. But what If, you cluster three batteries with the same length cable and the fourth battery is farther away with a cable that is 12 inches longer than the first three batteries.
My question, why is this a problem?
Using lithium batteries what is the actual “measurable impact” to your inverter performance and battery life. I know next to nothing about batteries, but they have BMS and a half-life that states that I’ll be dead when they hit 80 % of their life. Why not just make all the cables 12 inches longer. Or just forget about it and wire the fourth battery with a different length cable. Maybe the engineers can help.

Greeting Bill
I looked into this too a while back and found the gauge of the cable can make more of a difference than the balanced length, especially in the smaller size. So I up sized my cables and got as close to the same length as possible. So I agree with Brian on this Country Campers . To verify you can pose the question to your battery manufacturer.

Safe Travels
Keith

[Cate&Rob]

The whole issue with battery cable length is the resistance to current flow. When a high load is applied, even a short lived transient one, this can affect the voltage seen at the load. The solution to this is to increase wire size as much as you can, everywhere. Component manufacturers typically spec the smallest wire size that they think they can operate on and then usually advise to keep their device as close to the battery(s) as possible. My experience with this was a multi (lead/acid) battery bank powering a 3000W inverter in a marine application. I met all the manufacturers specs but still had the inverter kicking out as battery state of charge got lower. I significantly upsized the wires (going from the spec 1 ga to 4/0 ga) and had no more problems.

Rob

[TedS]

The idea behind having wire the same length is to have the same voltage drop at whatever current is being carried. Go to a larger wire size so that voltage drop is not significant and length equality will be of no concern.

[Country Campers]

So what you are all saying is if I have 2 batteries connected with 2 ga wire and a third battery a little further away 2/0 wire would be the best or would one have to go bigger than that? The whole wire gage size always gets me confused, 2 ga , 2/0 , what is the difference and is it enough?

Still learning,

Brian

[Cate&Rob]

Country Campers
Hi Brian,

The attached shows wire size for length and current. At the bottom is a comparison chart ( unfortunately without dimensions)

Rob

[TedS]

Note that the chart is based on the 10% and 3% voltage drop list on the left for the lengths of wire highlighted on the right. That let's you play games with wire size, current, and how sensitive you want to be about battery charger voltage drop. Or conversely how much current you can push with the voltage drop.

[howson]

On The Fly -- I went through a similar process as yourself back in 2019 during my install. It took some digging, but I found (on a different site) the reference from the person that helped me. He posted a response from Garret Towne (AMSolar engineer) that I subsequently confirmed. Here's the quote from the post:

Howard - I had spoken with both Garret and Battleborn on this article I posted above and they both said I was fine to go with method 2 in the link. This is also what I see most people do when hooking up their lithium batteries in parallel. The method you show will be more balanced (which was my concern) but they said it is not as critical with Lithium and the BMS system in the battery. They said this is a bigger issue with flooded batteries.

Method 2 was just simpler in my installation and I was all about trying to keep it simple the further I got into the project. Whichever method you go with I would try to keep the cable lengths the same (or consistent).... i.e. the above method have the longer and short cables the same length.

The "Method 2" being referenced is on this website: http://www.smartgauge.co.uk/batt_con...2b80LK-aokHDKk Below is a snip of just Method 2.





What's interesting is that Garret slightly modified Method 2 as shown in his hand-drawn sketch below. He further stated in the email to me, Balancing will happen as soon as the batteries are connected. The performance differences between diagrams <he's referencing the "Methods" on the website linked above> are so insignificant that consequences may never be noticed, but what I have attached is the best for the equipment you have.



Howard

P.S. If you interconnect with 2/0--even if some are a bit longer than others--and run 4/0 to the inverter IMO you'll be fine.

[Jlawles2]

I read an article somewhere a while back about multi battery hook ups. Basically they went through an elaborate explanation and came up with a fairly simple arrangement.

Lets take method 2 above as the basis. Number the batteries 1-4 from the top down. batteries 1&2 Are tied together in parallel as shown and 3&4 are tied together in parallel. Then from the center of each parallel connection those are tied together in parallel. And then out of the center of the last parallel connection cables are then tied back to the device.

I don't have a way to sketch on my Mac, but if I have time tomorrow I will sketch in CAD and upload.

[Scott'n'Wendy]

Chart is pretty general. For correct gauge selection you need to know the type of wire. Type can greatly affect gauge needed. For example, the chart calls for 4/0 wire for a 30' piece of wire to handle 200A. Doesn't say what kind of wire. If you bought 4/0 DLO wire it is rated for 405A. That is the free air rating which means wires separated from each other by the diameter of the wire.

[TedS]

Scott'n'Wendy I think you are conflating ampacity with the intent of the voltage drop- current-wire size chart. Those are different parameters.

[On The Fly]

Thanks, pretty sure I’m just going to buy a generator. And pick up some Advil.
I am not even capable of partially understanding this thread. I also understand why I majored in Computer Language.

The question remains if I place the same length cable between the batteries utilizing 2/0 gauge. (Connecting cables are now 12 inches in length and not six) Will performance suffer and can I measure it.

Or is the VOTE: connect battery 3 with 3/0 gauge.

Or the Vote from my Art/History friend…….Plug it in and press start!

Thanks again for all the thoughts and suggestions.

[TedS]

At the short lengths I don't think you will see any difference. Plug it in and press 'start'.

[Country Campers]

I agree that the difference will be negligible. Sorry if I lead to confusion I was trying to get some perspective from the masses as I am thinking of adding another battery or 2 and it will be hard to keep the wiring the same length without a lot of changes and rewiring. So from what I have gathered is use a little larger wire and forget about the rest.

Brian