Another broken stud story

[dielectric]

I think it would work. With the negative lead attached to the stud and the stud making contact with the cell terminal you're OK.

On my welding table, the negative lead is attached to the table, not the piece I'm welding. That's good enough.

It would. The stud would be in contact with the battery and the tig can point the arc in the right direction. I'm also just a hobbe/occasional tig welder but the setup would melt both pieces.

The 160$ question is would it melt them too much.

I have 4 out of 16 cells with detached studs, should probably get a refund... The capacity is great, the application is stationary... But I don't want yet another adventure trying to weld these myself.

3 spots around should be good enough for mechanical strength and electrical conductivity but the flat contact surface may get warped and then it's really a problem.

In the other hand if I tacked on a piece of aluminum angle and could use a bus bars in a vertical plane with as much torque as I want...

I've not decided.

 

[BobR]

You learn something new every day. I have never heard of conductive epoxy before. I’m not sure it would work to reattach a stud but it would certainly work to keep a stud attached especially if you put some between the buss bars and the exposed aluminum that surrounds the buss under the terminals before you snug the bolts down. It would virtually insure that the stud could not pivot side to side. I looked up conductive epoxy and I can think many times I could have used it where soldering would be impossible especially on small low power draw devices.

8331 – Silver Conductive Epoxy Adhesive

This product allows for quick, cold-soldering repairs. It can also be used as a solder replacement for bonding heat-sensitive electronic components, or for making conductive connections where soldering is not an option, such as when bonding to glass, soft metals, or plastics.

www.mgchemicals.com

 

[dielectric]

8331 – Silver Conductive Epoxy Adhesive

This product allows for quick, cold-soldering repairs. It can also be used as a solder replacement for bonding heat-sensitive electronic components, or for making conductive connections where soldering is not an option, such as when bonding to glass, soft metals, or plastics.

www.mgchemicals.com

Very cool epoxy only $44 on Amazon. This best version has 5.4x10-4 ohm/cm resistivity.
At 200A and 1mm thickness and 1square cm area the connection would dissipate 2W.

The 8331 "economical" version would dissipate 28W. Definitely too much.

Editing the arithmetic:

I suspect it is not too difficult to produce half a millimeter thik contact, with diameter of 1.55cm the area is 1.88 so resistance would be about

.00054×0.05÷1.88=0.000014ohm
×200A=0.0029W

Someone please check this. Because it may be acceptable.
I am going to risk $44 and test it on some scrap pieces of aluminum to actually measure the resistance.

 

[HRTKD]

Before I went down the road of TIG welding, epoxy or drilling/tapping the cell, I would look for a local laser welding shop. A quick Google search found one in my area.

 

[Hedges]

At 200A and 1mm thickness the connection would dissipate 2W.
The 8331 "economical" version would dissipate 28W. Definitely too much.

1mm? That's 40 mils. Can you get it down to about 2 mils or less?
There is no benefit to thicker epoxy unless you need to accommodate TCE mismatch.

Not that I like the idea of adhesive as high-current conductor. It is used for shingled solar cells, low current.

Aluminum grows native oxide. I wish it could be tin plated, which makes it OK for 200A busbars in a breaker panel.
Chromate treatment might be worth considering, but I'm not sure if there is a process to remove the oxide so underlying metal is made available. It is used for better ground bonding.

 

[dielectric]

I didn't mean to suggest making a thick joint like that. Please check my edited post.
I think 0.1mm is going to be hard to do.
But will test.

 

[dielectric]

I've started a separate thread about my own cells losing welded studs left and right.
My immediate decision is to return all 16 and pay $400 more and wait some more, or haggle with the seller for discount and play with epoxy and Tig.

 

[Hedges]

0.1mm should doable.
We had an epoxy die attach process. Epoxy was dispensed in multiple crosses of "X", so as pressure was applied it would not trap bubbles and create voids. This was done for ICs (about 1 cm^2) and MCM substrates (about 10 x 10 cm to 20 x 20 cm).
Bond line thicknesses were just a few mils. Goal was low thermal resistance.
Electrically, this was not a great contact because aluminum metallization had native oxide. Just to bias backside of die, not for high current.

If you can return and buy something with properly welded terminals, that would be better.

 

[brum]

0.1mm is pretty easy to be achieved if surfaces are flat. The bigger problem is what's going to happen with the oxidation and how strong this would be.

I would go for welding or tapping thread.