battery cell links

[Boron]

Hi Guys, being annually retentive, I have been puzzling over making connections between prismatics, using typically aluminium busbar links. This seems to be a retro step given that you mechanically bolt a bar between two cells constraining movement given the tendency to swell during the usage cycle (and delaminate causing loss of capacity over time - separate issue. The electrical connection between aluminium is a well known difficulty cos of the instant oxide insulation coating (and the reason electrolytics work btw. You have to use considerable force to break through this nano layer.
Using two AL surfaces to make contact seems to compound the issue. Some suggest a special metallic paste - does this work is it eg MIL spec approved or is it a scam?
However thinking out of the cell I got some kit to make a proper crimped ring terminal, a solid 8mm job looks good for at least 100A. Now I also acquired some SS grub screws to make a threaded stud - then I thought some 6mm2 solar cable will make a suitable FLEXIBLE link between cells - cheap enough and easy with my hydro crimper THEN lightbulb moment, some internal shakeproof SS washers to bite into the AL surface of the cells - which I will additionally protect with some Si grease. Good for 20 years? What do you think?

OBTW I will also enclose sensor wires in the crimps for cell volts

 

[upnorthandpersonal]

You can get flexible bus bars (plated copper, so no issues). I'm not a fan of aluminium bus bars and don't use them. The rigid bus bars that are included with many cell purchases are fine for most use cases (plated copper). You could even make flexible bus bars yourself like me:

Looking for 48V Battery Charger

Copper oxide is conductive, so it's not an issue. I use plain copper bus bars to join my inverters, charge controllers and batteries. No issues. Well it's not very good conductor is it ? That's why it needs to be cleaned off Otherwise I just wasted like 300 EUR on nickel strips and to build a...

diysolarforum.com

But only when you have time and equipment to do it. You can buy these types of bus bar (or other flexible ones) online, even from several off the cell vendors.

 

[upnorthandpersonal]

SS washers to bite into the AL surface of the cells

Most cells have welded studs these days, so that's not going to work since the surface area is smaller. And no, the smaller surface area is not an issue for current carrying ability.

Don't overthink this - we did that years ago when there were no welded studs or flexible bus bars readily available. Things have changed significantly since then.

 

[zedconnor]

Most cells have welded studs these days, so that's not going to work since the surface area is smaller. And no, the smaller surface area is not an issue for current carrying ability.

Don't overthink this - we did that years ago when there were no welded studs or flexible bus bars readily available. Things have changed significantly since then.

Hello what is your view on bimetallic AL-CU busbars? AL on the cell surface and CU on the top side.

 

[upnorthandpersonal]

what is your view on bimetallic AL-CU busbars? AL on the cell surface and CU on the top side.

Completely not needed. Plated copper is perfectly fine.

 

[Boron]

Most cells have welded studs these days, so that's not going to work since the surface area is smaller. And no, the smaller surface area is not an issue for current carrying ability.

Don't overthink this - we did that years ago when there were no welded studs or flexible bus bars readily available. Things have changed significantly since then.

Andy at https://www.youtube.com/@OffGridGarageAustralia/search?query=busbars had a lot of issues with busbars getting hot and studs becoming candles.

I am fixing to do some lab tests on these jointing methods. There is such a lot of disinfo around this subject (eg conductive grease, Using solid busbars on welded studs - these have oval slots rather than plain holes, so the contact area is questionable but I hope to present some facts rather than armchair speculation).

Perhaps someone can inform us what is done in EV battery packs?

 

[upnorthandpersonal]

Andy at https://www.youtube.com/@OffGridGarageAustralia/search?query=busbars had a lot of issues with busbars getting hot and studs becoming candles.

And Andy also confirmed the standard bus bars on welded studs are not an issue.

 

[Boron]

And Andy also confirmed the standard bus bars on welded studs are not an issue.

Indeed ok if you have welded studs. Lots of cells out there with threaded holes. His scattergun approach to testing is informative in some respects but frustrating in others when you are looking for an "real engineering" approach rather than "suck it and see" but I guess he needs drama to maintain his subscriber ratings and the inevitable freebies that are forthcoming.

My OP suggested what to do with the above non-studded cells

 

[upnorthandpersonal]

I think I missed the point where these didn't have the studs. I also have these in use, with my flexible bus bars I linked before and MG Chemicals 847 in-between to improve contact surface.