Improving Contact Area on Welded Stud Pads

Lt.Dan

Photon Sorcerer
Not true, there are very high grades of stainless that are still magnetic. These studs are most likely 18-8 stainless though. Which is mildly magnetic
 

Brett V

Solar Addict
Copy and paste from FSI:

18.8 Stainless Steel is the most widely used austenite steel in the 300 series and is also known as the 304. 300 series stainless steel has approximately 18% chromium, 8% nickel. 18.8 stainless steel also offers a tensile strength range of 80-200,000 psi and good corrosion resistance. 18.8 stainless steel benefits from increased resistance to corrosion better than the 400 series. It can be hardened through the cold working process and is non-magnetic.
 

Lt.Dan

Photon Sorcerer
Copy and paste from FSI:

18.8 Stainless Steel is the most widely used austenite steel in the 300 series and is also known as the 304. 300 series stainless steel has approximately 18% chromium, 8% nickel. 18.8 stainless steel also offers a tensile strength range of 80-200,000 psi and good corrosion resistance. 18.8 stainless steel benefits from increased resistance to corrosion better than the 400 series. It can be hardened through the cold working process and is non-magnetic.
18-8 can become magnetic when it is cold worked, ie turned into a bolt.

Even 304 SS can become magnetic if worked enough. I've seen it happen before my own eyes at work.
 

Short_Shot

Photon Sorcerer
Yes, when you are shopping for appliances like BBQ grills, etc. that are SS...bring a magnet with...
Eh. Mostly true but you need to watch out for some details.

Whether or not a magnet sticks to it indicates quality can be misleading as some grades can become magnetic during cold working processes and give you a false "positive" for a magnet despite still being a 300 series material.

You see this a lot in stamped 304 parts and sooometimes 316.
 

DerpsyDoodler

Photon Sorcerer
I didnt catch the whole thread, so don't know if this has been brought up: any reason a lug with a larger ring size couldnt go around that top pad and make contact with the bottom pad directly? A lug is plenty thick, and by the time you put a lock washer and/or flat washer, it should allow for torque pressure on the lug.
 

Brett V

Solar Addict
I didnt catch the whole thread, so don't know if this has been brought up: any reason a lug with a larger ring size couldnt go around that top pad and make contact with the bottom pad directly? A lug is plenty thick, and by the time you put a lock washer and/or flat washer, it should allow for torque pressure on the lug.
That was my original intent by enlarging the holes on the supplied bus bars. Best I could do was to get it sitting snugly on the aluminum weld so I was thinking a 15 mm inside diameter washer about 1 mm thick to fill the gap. The only thing I could find so far however is copper. I still haven’t ruled this out if I can find the right washer or shim.
 

DerpsyDoodler

Photon Sorcerer
That was my original intent by enlarging the holes on the supplied bus bars. Best I could do was to get it sitting snugly on the aluminum weld so I was thinking a 15 mm inside diameter washer about 1 mm thick to fill the gap. The only thing I could find so far however is copper. I still haven’t ruled this out if I can find the right washer or shim.
What about, instead of a washer or shim, use a wide enough ring terminal? After that it doesn't matter, right? busbar -> tinned copper lug , oxguard where prudent, current shouldn't flow through anything above the lug, so ss, copper or whatever washer and a lock washer.

What I'm proposing is trying to ignore the top pad. Is there enough contact area on the bottom pad for high current application?
 

Lt.Dan

Photon Sorcerer
As stated above there is no "surface" or "bottom pad" as it is just an uneven weld that would not provide adequate contact surface, even if it was more in^2.
 

stienman

Solar Addict
Thanks all for your comments and expertise! Assuming I get studs like these, I'm not going to do the crush washers initially. I don't anticipate moving more than 30-50A normally, with peaks around 100A, and the contact area of the smaller pad is more than sufficient for that without significant losses.
 

Bob B

Photon Sorcerer
According to Amy .... the people who do her welded studs are telling her you can do 10 nm of torque on them. This is 2.5 times as much as the threaded pads with a stud.
That amount of extra torque by itself will probably result in a better electrical connection than the threaded pads ... if you add an aluminum crush washer to increase the surface area even more .... You should be good to go.
 

Brett V

Solar Addict
As stated above there is no "surface" or "bottom pad" as it is just an uneven weld that would not provide adequate contact surface, even if it was more in^2.

on the EVE cells, this entire pad is an aluminum battery terminal.
 

Attachments

  • shoulder_LI.jpg
    shoulder_LI.jpg
    1.2 MB · Views: 11
Last edited:

Brett V

Solar Addict
According to Amy .... the people who do her welded studs are telling her you can do 10 nm of torque on them. This is 2.5 times as much as the threaded pads with a stud.
That amount of extra torque by itself will probably result in a better electrical connection than the threaded pads ... if you add an aluminum crush washer to increase the surface area even more .... You should be good to go.

My small torque wrench hasn't been calibrated for a few years but I just went out and tried 10 nm... nothing broke.
 

Colonel.lp

Solar Enthusiast
I don't know if anyone else saw that I asked Amy what the current capacity of the welded studs are, she said her supplier has them rated at 300amps, I'm not sure if that's realistic, but the more I think about it, the more I think the contact area can probably carry a lot more than we think it can as long as the oxide is cleaned off. Think about the contract area on high powered relays, it's not huge.

Harking back to my physics days:

Resistance =ρl/a (where ρ is resistivity, l is length, a is area)

so on a contact patch l(length) is very small compared to a length of cable, so should be able to carry much more current without heating up due to lower resistance. .

Before I came across this thread I had mulled over what you are attempting with washers, and decided that unless I could find a washer that is soft enough, there is potential for the weld causing an unparallel washer therfore reducing the mating surface even more, especially when using solid busbars where adjacent studs may be in vastly different planes from one another due to cell assembly and stud placement differences. (On my original eve 280 cells with the tapped terminals, a swipe with a hone showed that adjacent factory terminals were unparallel to the point that a busbar would only be sitting on about 30% of the total area) In the end I decided that using cable with lugs was the best way to maximize contact area, and silicon grease to protect from corrosion. We will see how it goes when I get them in service.

IMG_20210827_001722_684.jpg
 
Top