Connecting packs with brass spacer?

[Rasmusm88]

Hi all.

So my current 14s200p packs are connected with a 25mm cobber spacer, like on the picture.
It works great and about to put another 14s200p in service, but I'm out of cobber hehe, I could cut them in half though.

My question is, we have a bunch of 16mm round brass laying around here on my job. My thought was to cut some spacers and drill a 10.2mm hole through for the bolt, M10 bolt.

Which will end up with a square section of 122mm2 contact area. 8*8*3.14 - (5*5*3.14) = ~122mm2 but in brass, which is less conductive than copper according to this:

Electrical conductivity of metals

I'd read in a lot of places that lights, etc are built with brass instead of aluminum/aluminium for better electrical conductivity. However, real data proves otherwise. In order of electrical conductivity (relative to copper) Material IACS % Conductivity Silver 105% Copper 100% Gold 70%...

www.candlepowerforums.com

Then my thought was to use aluminum, but galvanic corrosion then, or am I over thinking it I have sanded the cable lugs a bit to remove the bumps and burrs from manufacturing, which resulted in bare copper exposed below the plating.

What do you think, brass ok?

Have a good day

 

[Rasmusm88]

I managed to find some cheapish cobber. So I will manufacture some spacers out of that instead.

 

[Korishan]

Yeah, don't mix copper and aluminum without having a brass interconnect. There'll be galvanic corrosion for sure. I found out that you can't even have aluminum with lead. Connected some CCA cable to lead car battery lugs. I hadn't use those in a couple years and the ends just fell off the cables

But overall, yes brass would be fine. You just want to make interconnect a little bigger than you'd have for the same rated current size of copper. But, tbh, anything like you have in your picture would be just fine unless you plan on 200A for any length of time

 

[Rasmusm88]

Thanks, yea now with second 14s200p it will half the current draw. Was originally 100a, and mppt able to push in a max of 125amps. So batteries are much more idle and less load now honestly surprised by how well old laptop batteries handle it. Been in service for 1.5year, and I never balance, they all stay within 0.02v.

I'm only using batteries with max 15% degradation though. These new 14s200p are ebike batteries, really looking forward to this summer

 

[Korishan]

Nice clean look, great job!

 

[Rasmusm88]

Thank you what is your opinion on this for balance wires. Using stainless bolts, like in the first picture.
Thought about drilling a hole in the bolts and making a M4 thread for the balancing wire with a lug to batrium. I know stainless is not as great a conductor but, in my first picture you see the balancing wire janked in between a washer and a nut anyways, and that's working great.

 

[100kwh-hunter]

watch out please.
I like KISS, keep it simple stupid.
just krimp a lug on the bms wires and stick that in between your existing brass and batt lugs.

More components mean higher IR

 

[Rasmusm88]

That would not work out well, to stick it between the cobber spacer and batt lug. That will imo cause higher IR though.

 

[Boron]

A very tidy job. When you bolt it all up, will you be able to monitor for hot spots (as these are old used cells). You might like to consider putting a hood over the top to capture the heat produced by the cells. use a few of those cheap temp loggers by Elitech , you can store a months readings at a time and display graph on pc. The button cell lasts a year - great piece of kit IMHO. Used in horticulture and food industires.

 

[Korishan]

Thought about drilling a hole in the bolts and making a M4 thread

This would work, tbh. as long as you have plenty of work. But I also agree with @100kwh-hunter about keeping it simple. However, if due to the size of the primary connections, then alternative options could be needed.
You could also take a plate of copper/steel/brass, drill a large enough hole for the primary connection, then a smaller tap for the balance wires. So kind of a bus block for a bus bar for a bus lead
And tbh, if you can get brass bolts, that'd be better than Stainless steel. Checking your link with the electrical conductivity, SS is a mix of Steel and Nickel. The more nickle, the higher the conductivity. However, they will probably never be 50% or higher on the nickel side. And Nickel is only 22% compared to Copper

 

[Rasmusm88]

I can order brass bolts relatively cheap actually, thanks I might do that

 

[hbpowerwall]

I did that back in 2017 worked a treat then and still does now