Another broken stud story

WindWizard

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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.
I am not sure I am following your logic. The current has to have a path to go through. If the ground is connected to the stud then where does the current go through? If the electrode is placed on the same piece as you are trying to weld then there is no current path. you would need to have one end on the flat area on the Cell and the other on the stud to have a current path so that the weld takes place.
 

Fast1one

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Interesting discussion. I don’t think it’s something I’m willing to try due to the aforementioned heat issue. There just isn’t a lot of material for that heat to go.

Definitely wouldn’t want to weld it all in one go. One or two tacks at a time and letting it cool in between.

If the return is attached to the lug that should work. Same concept as if you have a practice piece of metal and you hook your ground directly to it. The current will find a way lol.
 

time2roll

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I've been TIG welding aluminum for just over a year now. My welds are solid, but fugly. If this were my cell, the questions in my mind would be:
1. Weld the entire perimeter of the stud or spot weld? Welding the entire perimeter would create a lot of heat. Spot welds, not so much.
I would think the entire perimeter could be done in sections between cooling sessions. Maybe 3 to 6 passes after a tack weld.
 

Rossman

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If the ground is connected to the stud then where does the current go through?
So there's the pad, on the cell, and then the stud, which you want to weld on. You ground the stud and use <whatever> means to hold it in place on the pad, then the current goes from the pad through the stud to ground, I guess?
 

Bobert

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So there's the pad, on the cell, and then the stud, which you want to weld on. You ground the stud and use <whatever> means to hold it in place on the pad, then the current goes from the pad through the stud to ground, I guess?
I’m have never welded aluminum before but tons of steel. Generally you only ground one of the objects that you are welding the current for welding passes through from one object to the other as all surfaces must be clean and touching each other to get a good weld.
 

Rossman

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I’m have never welded aluminum before but tons of steel. Generally you only ground one of the objects that you are welding the current for welding passes through from one object to the other as all surfaces must be clean and touching each other to get a good weld.
Isn't that what my post said?
 

WindWizard

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Isn't that what my post said?
No I think it is like apples and oranges. Current needs to pass between the aluminum pad and the stainless steel stud assembly to work. If you could somehow get the ground to the aluminum pad and then use the electrode to weld the stainless steel stud assembly, then you would be able to do it. I just do not see how connecting the ground to the stud is going to weld anything.
 

RobertGreen

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I guess my point is you can rely on these cells until you can’t. Once upon a time Basen had a decent reputation. Maybe Docan is different. I hope so 🤞
Please understand that Docan and Basen are both just resellers; they don't have anything to do with how these cells are manufactured or modified and their reputation is only relevant in terms of how they provide service as a merchant.... I've been very happy with doing business with Docan, and I would use them again (and I've got some cells from Basen in the past that were a good price and good quality at the time), but I know that they just pass along whatever comes to them. This is a buyer beware market
 

HRTKD

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No I think it is like apples and oranges. Current needs to pass between the aluminum pad and the stainless steel stud assembly to work. If you could somehow get the ground to the aluminum pad and then use the electrode to weld the stainless steel stud assembly, then you would be able to do it. I just do not see how connecting the ground to the stud is going to weld anything.

You're not welding the stainless steel stud. You're welding the aluminum (that surrounds the stud) to the cell's terminal surface. The negative welding lead attached to the stud will work just fine, as long as the aluminum (that surrounds the stud) is in contact with the cell terminal's surface. Like Fast1One said, the current will find a way.
 

Bobert

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Well it finally happened. After months of being careful I’ve damaged a cell with no spare available. I’m generally pretty careful and this experience has me dumbfounded.

Before you ask, I’ve never so much have hand tightened these with a nut driver. I can’t imagine going over the recommended torque ratings without leverage, much less since I am of average build and below average strength but I digress….

After capacity testing, load testing for months it was finally time to lay the cells to rest. I moved them into the bus conversion where they experienced mild temperature fluctuations of around 50F to 70F. Today I went to check the cell voltages for the final time before installing the bus bars and I found a stud just resting on the terminal, no longer welded. Note I moved the stud in the following picture to show the terminal surface:

View attachment 93076


There appears to be a complete lack of penetration on the weld. I’m guessing the (mild) torquing over the months and temperature shift finally did this in. Needless to say I don’t trust these AT ALL for an RV application and I will be ordering replacements from a different vendor. I’ll be selling these at a loss locally with a fat disclaimer of the issue.

FYI, they originally came from Shenzhen Basen Technology Co according to the label but I purchased them through an intermediary. Had I known they were coming from a seller with less than stellar ratings on this forum, I would have reconsidered.

So what’s the lesson? I’m not really sure. Definitely use a torque wrench. But I don’t think that was the problem here. Stay away from studs? I will certainly be switching to screw in terminals from Docan since I need these fast. I find the fixed length of the studs rather limiting.

These are beyond my ability to repair and likely for most DIYers. But if anyone in the central coast of California needs some cheap EVE 230AH cells I’m your man.
The main problem here is that the weld is only on one side. This is a matter of quality control. Even a very good weld only on one side will fail easily. It’s possible none of the other cells have this issue.
 

WindWizard

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I would think that conductive epoxy would work rather than take a chance with one sided welding.
 

Bobert

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I would think that conductive epoxy would work rather than take a chance with one sided welding.
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.
 

740GLE

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Conductive epoxy rated at 100s of amps possibly 100c. JB weld have a new product line? Lol

I’d love to see this as an option but skeptical such thing would last long term.
 

Hedges

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It appears cells were designed to have busbars welded connecting them in a pack. The ones we've seen pictures of have a busbar shape that allows expansion/contraction. These were generally round terminals and busbars had around hole fitting around them, laser welded in a circle.

The first cells for DIY people on the forum bought had 6mm, 1 thread/mm tapped holes. The holes were 6mm deep and had 4 full threads, last two tapered. In soft aluminum, easily stripped, and many stories of repairs, but also many packs built and used. The tapped holes were sometimes very sloppy, probably done with hand tools (crooked, etc.)

One issue I have with single screw connections is that force on the wire could unscrew the connection. Not a problem for busbars of a pack secured against movement, but for connections on the end you need to prevent that.

Welded studs were offered and seemed great, but some broke off like these. It's a matter of weld quality, as observed.

Some cells have been offered with an aluminum tab carrying a stud, but with a hole fitting around terminal and laser welded like original pack busbars. Those seem like the best I've seen, but I think they still have native aluminum oxide in the contact area.


I would not expect conductive epoxy to be good on aluminum terminals. Mechanically it could bond, but doesn't break through aluminum oxide.

The only "right" ways of using aluminum I'm aware of are welded (generally laser, avoids the overheating of cells), Crimping (utility lineman puts terminals on power line cables, and tin plated aluminum (extensively used in electrical panel busbars, screw terminals, etc.) And finally, for field connections to aluminum wire that involves cleaning oxide, using inhibitor, clamping with a listed terminal.

I haven't welded aluminum or used TIG, just stick welding. But I think only laser will be fast enough to not overheat the cell. It might be possible to tack multiple spots with TIG, cooling in between. But regard that same as if you were trying to weld a canister of explosive. Cells outgas flammable materials, and your welder provides source of ignition. I think very bad things could happen attempting to manually weld these cells. Should not be attempted unless there is some sort of firewall and manipulator that keeps operator out of harms way. In other words, chucking the cell would be a prudent course of action rather than DIY welding. (but drill and tap, with precautions, could be considered.)
 

Bobert

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The best holding power you can get from a threaded hole is to thread in a stud and tighten the wires or busbars down using a nut. The friction of turning a bolt through aluminum threads under tension tends to strip them.
 

740GLE

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Some vendors are carrying EVE 280 with welded pads with double threaded M6 holes with helicoil inserts.

I can’t see anything being better than that, again unless the welded connection fails.
 

fshan

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Mar 30, 2022
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You could drill one and find out how deep the metal is. The others might be salvageable. Be careful.
I agree. I would take a 1/64th drill bit 1mm at a time and find enough meat to tap 2 or 3 threads for jb weld careful not to get any on the pad OR I would find bottom and let the gas out. one or the other. Right or wrong that is what I would do. Mail it to me I will do it. Since it costs so much for that pad I doubt the pad is thick enough to get up to a full thread on a bottom tap but I would find out. If I could get that deep with a small drill bit without finding bottom I would drill and tap for 1 thread of 6mil and jb weld it careful not to get any on pad. Then bussbar laid flat on pad, nut on top.
 

Fast1one

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Mar 3, 2021
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I appreciate everyone’s advice. At this point in our build it’s really not something we want to deal with. We will likely move on and hope that the replacements fair better in the environment in which they will be installed in.

Definitely knew the risk going in. Even after the mishap it’s still worth it to build our own pack with the REC 12V BMS which has been really easy to work with. If I were to do it again though I would definitely look into a 48V system with something prebuilt. Idiosyncrasies and all that come with that option.
 
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