Improving Contact Area on Welded Stud Pads

Horsefly

Photon Sorcerer
Joined
Dec 12, 2020
Messages
920
Location
Denver, mostly
After the early adopters complained about how easy it was to strip the threads on their prismatic LiFePO4 terminal pads, the market seemed to have responded by offering studs welded onto the original pad, rather than drilling and threading a hole for a bolt. That certainly sounded good to those of us who read all the posts about stripped threads.

For some with the studs, it appears the contact area on the terminal is quite sufficient, and may be almost as big as the original terminal pad. For others of us, the stud is mounted to a pretty small 10mm round pad, as shown in this photo:
IMG_20210810_091811324.jpg

That is already a very small area to give enough contact to a bus bar if you intend to carry significant current. There is a slightly larger circular pad (13mm diameter) below the 10mm pad, and then the original terminal pad. To make it worse, most of the good bus bars have a groove rather than a single hole, to allow some variance in spacing the cells. With the hole / groove sized a bit larger than the 6mm stud, it is obvious that the bus bar makes only a small amount of contact with the terminal:

IMG_20210810_090503065.jpg

When I noticed this issue I brought it up in @Michael B Caro's thread for the group buy (my original post about it was here). After some discussion about it, my good buddy @Brett V made the brilliant suggestion (here) that some aluminum crush washers (like used to seal the plug on the bottom of some oil pans). So I went out and bought some.

I found two that kinda fit the bill, so I thought I would post about them. First there these: https://www.amazon.com/gp/product/B01ER3U3XY

They have an inside diameter of 12mm, so it is a bit of a loose fit around the 10mm pad, but it does then make contact with the 13mm pad below, and at 2mm thick the top is level with the other pad, so a bus bar can make pretty good contact.

The second one I bought wasn't even a oil pan crush washer, but some sort of stamped then for making jewelry (?): https://www.amazon.com/gp/product/B07SR2BDCK

These have an inside diameter of around 9.3mm, so it is too small to fit over the 10mm pad. However, with a small amount of filing it fits well. It's tight, and makes good contact with both the 10mm pad and the 13mm pad below it. It again looks to be the right thickness so that it is level with the 10mm pad. Here's a photo with both on the studs. The one on the left is the 9.3mm jewelry washers, and the one on the right is the 12mm compression oil pan washer.

IMG_20210813_153932097.jpg

Anyway, I hope this helps!
 
Last edited:

Horsefly

Photon Sorcerer
Joined
Dec 12, 2020
Messages
920
Location
Denver, mostly
I like the crush washer idea to get a little more surface contact.

Your first Amazon link isn't working for me .... is this the item? https://www.amazon.com/Aluminum-Gaskets-Plus-Parts-House/dp/B01ER3U3XY/ref=sr_1_4?
You got it! I Thanks @Bob B. I fixed the link in my post.

AN UPDATE: Upon further inspection, the jewelry item isn't quite 2mm thick, so if it goes all the way down around the little 10mm pad, a bus bar won't actually make any contact with it. The compression washer / gaskets work better.
 

Horsefly

Photon Sorcerer
Joined
Dec 12, 2020
Messages
920
Location
Denver, mostly
Is the oval silver part of the terminal conductive?
If you mean the top layer pad, 10mm in diameter, I had the same question in the other thread. I thought it was stainless steel, but someone (which I could give credit here) pointed out how the studs are built, and that the pad is actually aluminum. So, the answer is YES.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
6,073
Location
Somewhere South of Denver
Looks like a stainless steel bolt that has aluminum formed around it. I saw a welding video that did a similar thing. It was a tight bond, but the two metals were not welded together.
 

Stepandwolf

Solar Addict
Joined
Nov 14, 2020
Messages
635
Looks like a stainless steel bolt that has aluminum formed around it. I saw a welding video that did a similar thing. It was a tight bond, but the two metals were not welded together.
Correct, the aluminum is basically molded around the SS bolt. Other than to save a penny, there isn't a reason for the pad to be 10mm.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
6,073
Location
Somewhere South of Denver
Absent a better solution, the washer around the base seems reasonable. I would use an aluminum washer, but finding one that is the correct height and with the right diameter hole could be challenging.
 

Stepandwolf

Solar Addict
Joined
Nov 14, 2020
Messages
635
Absent a better solution, the washer around the base seems reasonable. I would use an aluminum washer, but finding one that is the correct height and with the right diameter hole could be challenging.
I provided a link above to what appears to be the correct one:

A quick search found these

10mmX18mmX2mm
 

Brett V

Solar Addict
Joined
Apr 5, 2021
Messages
214
Location
South Central Pennsylvania
Looking at how the welded stud played out, I'd have opted for the drilled and tapped flat electrode given the choice... with the understanding I need to use a torque wrench and not treat it like a ball joint locknut from a 1968 Kenworth. I think the aluminum crush washer can be either sanded down a few thousandths or slightly compressed if needed.
 

Stepandwolf

Solar Addict
Joined
Nov 14, 2020
Messages
635
Looking at how the welded stud played out, I'd have opted for the drilled and tapped flat electrode given the choice... with the understanding I need to use a torque wrench and not treat it like a ball joint locknut from a 1968 Kenworth. I think the aluminum crush washer can be either sanded down a few thousandths or slightly compressed if needed.
yikes, everytime I think I have made my decision, someone else comes along and makes me rethink the process. My current 8 cells are Lishen with the thread. So far, I didn't strip a thread, but I haven't installed them yet. At least for the studs, if you screw something up, it is more recoverable than the threaded hole, or at least it seems to me.

I am buying another 8 cells, and my domestic supplier has the threaded but not the welded. They can ship welded from China, but then this suppliers price is higher.
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,379
yikes, everytime I think I have made my decision, someone else comes along and makes me rethink the process. My current 8 cells are Lishen with the thread. So far, I didn't strip a thread, but I haven't installed them yet. At least for the studs, if you screw something up, it is more recoverable than the threaded hole, or at least it seems to me.

I am buying another 8 cells, and my domestic supplier has the threaded but not the welded. They can ship welded from China, but then this suppliers price is higher.
When a decision keeps going back and forth ... you will likely be OK either way .... or fail either way ... sorry had to throw that last part in there ....LOL
 

Brett V

Solar Addict
Joined
Apr 5, 2021
Messages
214
Location
South Central Pennsylvania
A stripped tapped hole is more recoverable than a bad experience with a stud. I can easily put a helical thread insert in a stripped hole or just drill it out to the next size and tap new threads. On the 230 amp EVE cells I got, the supplied buss bars are too thick to stack and have enough threads to work with. The studs are too short...I already stripped the top two threads off of one just using a nut driver. Once I have assembled all the cells in series, this will not be a problem but for top balancing, it's a little dicey.
 
Top