Advice on rethreading a welded stud

[Hedges]

Sorry not sure what you are referring to?

My goal is to end up with a usable welded stud and attach the busbars some as you normally would, although I am leaning towards using a coupling nut instead of a standard nut that way it uses all available threads vs just a couple above the bus bar and balance leads.

Gotcha.
Coupling nut because it is longer, sounds good.
I thought you meant coupling nut to make a female thread, busbar on top of that, which would have been poor electrical path.

Make sure cable connections are limber enough that cable doesn't loosen its nut.
People here have assembled and used batteries with tapped holes, welded, studs, others, but all seem to be an aftermarket kludge which was done to make EV reject cells marketable to the solar storage market. Many tales of stripped, pulled off, etc.
And then some have poor contact, hot busbars and apparent voltage deviation of cells. Make sure you deal with native oxide and use some sort of corrosion inhibitor.
A few newer welded terminals look more robust.
One guy got himself a bank of cells with welded busbars between them (as replacement system, after catastrophic failure.)

 

[InMyImage]

Be really careful and use quality dies and cutting oil then.

thanks for reminding me about the cutting oil. I’m on the road full-time and all my tools and supplies are in storage so might not of thought about it and had to make an extra trip or a second order to get some.

 

[InMyImage]

Gotcha.
Coupling nut because it is longer, sounds good.
I thought you meant coupling nut to make a female thread, busbar on top of that, which would have been poor electrical path.

Make sure cable connections are limber enough that cable doesn't loosen its nut.
People here have assembled and used batteries with tapped holes, welded, studs, others, but all seem to be an aftermarket kludge which was done to make EV reject cells marketable to the solar storage market. Many tales of stripped, pulled off, etc.
And then some have poor contact, hot busbars and apparent voltage deviation of cells. Make sure you deal with native oxide and use some sort of corrosion inhibitor.
A few newer welded terminals look more robust.
One guy got himself a bank of cells with welded busbars between them (as replacement system, after catastrophic failure.)

Wow, not sure how well I would trust welded on busbars partially because of concerns that they might not be sized for future load changes vs what they were when I bought them, issues dealing with a bad cell in the pack, issues if they aren’t seated correctly on the terminal during the welding process because unless two components are not being compressed in some way during the weld, the weld bead shrinks really quickly and affects fitup on the opposing side, it’s one reason when welding you make pairs of small “tack” on opposing sides of the part, preferably at least 2 sets 90 degrees from each other. My understanding of the process for these welded studs is that the screw portion is enased in the aluminum shoulder amd screwed into a “standard” stud hole then laser welded all around which is quick and uniform all around because of being held in place mechanically during the weld. Unfortunately from pictures around here, it looks like some suppliers aren’t using an appropriate shielding gas flow rate so the welds look like crap visually and are weaker structurally but probably sufficiently strong for this application.

Actually had a thought today of using a set screw when finalizing the pack to help reduce the chances of the nut loosening during travel… The length of a coupling nut definitely makes that a possibility but will probably wait till I see how well they hold with removable Loctite on the threads.

 

[Hedges]

Stud on top with an aluminum top hat welded on was a kludge.
I think original design had busbar with a hole in it, fitting around the cell terminal and welded.
More recent cells for DIY had that style weld and dual threaded holes in the attached terminal, might be pretty good.
We've also seen original busbars formed with bends to they have some compliance, jumpered from cell to cell.

Where it has a bolted connection, I would want plated surface.
PG&E's terminations to aluminum wire are crimped, so that appears to be fine as well.

 

[HRTKD]

My understanding of the process for these welded studs is that the screw portion is enased in the aluminum shoulder amd screwed into a “standard” stud hole then laser welded all around which is quick and uniform all around because of being held in place mechanically during the weld.

This is not how I think the laser welded studs are implemented. I suspect that the cell terminal is solid, with no hole in it at all. From the pictures I've seen of laser welded studs coming loose, I don't think the stud is in anything other than the cap that it is encased in.

 

[InMyImage]

This is not how I think the laser welded studs are implemented. I suspect that the cell terminal is solid, with no hole in it at all. From the pictures I've seen of laser welded studs coming loose, I don't think the stud is in anything other than the cap that it is encased in.

In some ways that would make sense but the internal mechanical connection would seem to make a better overall connection especially given the tiny shoulder are for contact with the busbar. I saw someone here describe the process but have no idea who or which thread.

Pretty confident that the next set of cells I buy will be the EVE’s with their new welded terminals that have a sizable flat area and 2 screw holes

 

[MattiFin]

What was the reasoning in those other threads?

Stainless nut on stainless bolt is asking for trouble. Stainless/stainless pair galls(friction welds) together sometimes with suprisingly little effort and once that happens the parts are solid assembly.
Using anything else than stainless nut solves the galling tendency. Brass, galvanized or silver plated stainless.

 

[HRTKD]

Stainless nut on stainless bolt is asking for trouble. Stainless/stainless pair galls(friction welds) together sometimes with suprisingly little effort and once that happens the parts are solid assembly.
Using anything else than stainless nut solves the galling tendency. Brass, galvanized or silver plated stainless.

I was not aware of this with stainless steel. A quick web search found this article on galling:

How to prevent galling on stainless steel bolts | Global Manufacturer & Distributor of Component Solutions — Essentra Components

Galling is a form of severe adhesive wear. It happens during installation to fasteners made of alloys such as stainless steel, aluminium and titanium.

www.essentracomponents.com

 

[time2roll]

Stainless is a bit overrated. Corrosion resistance is not needed nearly as much as with a lead-acid battery.

 

[MattiFin]

Actually had a thought today of using a set screw when finalizing the pack to help reduce the chances of the nut loosening during travel… The length of a coupling nut definitely makes that a possibility but will probably wait till I see how well they hold with removable Loctite on the threads.

I'd use thick washers and disk spring washers (belleville washers)

Disk spring washer is used in industrial busbar connections etc and it helps to maintain the clamping load on the connection even if the nut would slightly loosen on thermal cycling loosening the joint.

Rethreading stainless male thread to smaller size is bad idea at best.
1. Threading dies are not designed to cut oversize stock, so you would need to machine the studs to nominal starting dimension before threading die. Easier said than done when the stud is solidly mounted to the cell.
2. M5 would lose quite a bit of stregnth compared to M6, M5.5 has different thread pitch and is too close in size leaving partial crappy thread with some of the thread missing here and there. (and is extremely non-standard size)

 

[InMyImage]

I'd use thick washers and disk spring washers (belleville washers)

Disk spring washer is used in industrial busbar connections etc and it helps to maintain the clamping load on the connection even if the nut would slightly loosen on thermal cycling loosening the joint.

Rethreading stainless male thread to smaller size is bad idea at best.
1. Threading dies are not designed to cut oversize stock, so you would need to machine the studs to nominal starting dimension before threading die. Easier said than done when the stud is solidly mounted to the cell.
2. M5 would lose quite a bit of stregnth compared to M6, M5.5 has different thread pitch and is too close in size leaving partial crappy thread with some of the thread missing here and there. (and is extremely non-standard size)

Thanks for the input. I have a tap and die set arriving today, covers like M3 - M12, coarse and fine threads, figured having something on hand that will cover and bolts I might need to repair in the future would be good to have.

Couldn't find and coupling nuts shorter than 10mm and those wouldn't arrive in time for me to get this system installed within the next week so ended up getting M6 Serrated Flange Nuts. If they don't hold, I'll look into spring washers or nuts with the attached washers with teeth that really bite into the metal.