Terminal Damage - Proper Connection - LifePo4 with Flexible Bus Bars

[LohaDragon]

These terminals appear to be arcing or even melting. This battery saw very light duty for a short period while testing minor electrical components, but will drive an electric vehicle at far greater loads.

I wire brushed black residue off the terminals before taking the picture. The terminals look deformed where the black residue was. I don't recall them arriving like that.
Only one of the bus bars has arc marks.

There seems to be a significant space between the terminal stud and the bus bar. But not larger than the factory supply bars. The connection is flex bus bar, stainless steel washer, BMS terminal ring, stainless steel nut. The nuts were properly torqued I believe and you can see the terminal base impression on the bus bar.

Considering tapping copper washers to fit the terminal studs, then placing bus bar on top.

What is happening and how to fix?

Thanks for all I've learned in this community!

16S battery, 310AH, 3.65V, flexible copper bus bars, sourced from Alibaba grade A

 

[LithiumSolar]

That just looks like messy laser welding to me. If it got hot enough to melt metal like that from arcing or heat due to resistance, the plastic would be totally melted.

 

[Hedges]

If that's an arc on the busbar, must have had better contact to the stainless threads than to the aluminum terminal.
Needs oxide scrubbed off, corrosion inhibitor, proper torque. And not moved in a way that loosens it back up.

 

[timselectric]

Third picture looks like a washer was used.
Was it between the bus bar and battery terminal?
This could be the problem. It would create a bad connection and lots of heat.

 

[740GLE]

You said light duty loads, what’s your definition 3A? 10A? 50A?

Why not mention the load value that was used for your testing?

 

[LohaDragon]

That just looks like messy laser welding to me. If it got hot enough to melt metal like that from arcing or heat due to resistance, the plastic would be totally melted.

Thanks! Didn't notice it when installed a year ago, so felt like a gut punch. Will reset the battery and check.

 

[LohaDragon]

If that's an arc on the busbar, must have had better contact to the stainless threads than to the aluminum terminal.
Needs oxide scrubbed off, corrosion inhibitor, proper torque. And not moved in a way that loosens it back up.

So perhaps it was just one bus bar not torqued and remainder factory welding. Will do!

 

[LohaDragon]

You said light duty loads, what’s your definition 3A? 10A? 50A?

Why not mention the load value that was used for your testing?

Appreciate the direction. About 10 amps, that was blowing fuses. 30 amps for charging. I'll monitor with the smart shunt and full load test.

 

[LohaDragon]

Third picture looks like a washer was used.
Was it between the bus bar and battery terminal?
This could be the problem. It would create a bad connection and lots of heat.

Terminal, bus bar, bms ring terminal, washer, nut is the sequence used.

 

[OM617YOTA]

I wanted to avoid that same issue, so here's what I did.

Drilled out my bus bars so they'd fit lower, over the shoulder, and on the weld itself. Cells are compressed in usage, but I left a little wiggle room, just in case.



The shoulder was slightly higher than the bus bar, so I countersunk the nut slightly to match.



Weld is aluminum and will make aluminum oxide in open air very quickly. Aluminum oxide doesn't conduct. I wire brushed the aluminum terminal with a small stainless wire brush chucked in a drill to remove the oxide, wiped clean with naphtha, applied lots of Ox-Gard on the terminals, and then torqued it down. Not particularly happy about five dis-similar metals in close proximity in an electrical terminal, but used what I had available. Aluminum battery terminal, stainless stud, copper bus bar, zinc plated steel nut. Stainless on stainless will gall, but I probably should have used an aluminum bus bar and a plain steel nut, not zinc plated.

Hasn't been in service long, but it's worked great so far. Pulling ~80a and watching with a thermal camera shows no heating. I plan to inspect, check torque, and watch with the thermal camera frequently. Frequent inspection is key., lots of things will work fine at first, but adding a couple years of thermal cycling and oxidation can change that equation.

 

[Hedges]

So long as you don't misjudge required countersink depth. Some pictures appear to show tall shoulder.
Flat end on drill could give more clearance. I used to drill with standard point first, then a drill I sharpened flat, to countersink socket head cap screws.

Alternatively for your situation I might have used an oversize split lock washer (to clear shoulder), and large (possibly fender) washer if needed.

 

[OM617YOTA]

The OP might have a taller shoulder.

Complete non issue on mine. The nuts actually torqued against the bus bar without the countersink just fine, I was doing the braces and belt thing.

 

[Alkaline]

OP I think you made the whole situation worse, also you exposed the copper on the bus bar which is not going to play nice to the aluminum terminal.

 

[dielectric]

I wanted to avoid that same issue, so here's what I did.

Drilled out my bus bars so they'd fit lower, over the shoulder, and on the weld itself. Cells are compressed in usage, but I left a little wiggle room, just in case.

View attachment 158240

The shoulder was slightly higher than the bus bar, so I countersunk the nut slightly to match.

View attachment 158241View attachment 158242View attachment 158243

Weld is aluminum and will make aluminum oxide in open air very quickly. Aluminum oxide doesn't conduct. I wire brushed the aluminum terminal with a small stainless wire brush chucked in a drill to remove the oxide, wiped clean with naphtha, applied lots of Ox-Gard on the terminals, and then torqued it down. Not particularly happy about five dis-similar metals in close proximity in an electrical terminal, but used what I had available. Aluminum battery terminal, stainless stud, copper bus bar, zinc plated steel nut. Stainless on stainless will gall, but I probably should have used an aluminum bus bar and a plain steel nut, not zinc plated.

Hasn't been in service long, but it's worked great so far. Pulling ~80a and watching with a thermal camera shows no heating. I plan to inspect, check torque, and watch with the thermal camera frequently. Frequent inspection is key., lots of things will work fine at first, but adding a couple years of thermal cycling and oxidation can change that equation.

the welds can not be flat enough, at least on the cells that I have
i agree that the surface around the stud is very small but I would be much more concerned with flatness.
could you post a picture of what the surface looks like? (the one that the bar is sitting on after the mods)

 

[OM617YOTA]

My terminal welds are flatter than most, but indeed not ideal. In the absence of an ideal option, I did what I did.

Definitely take my posts as "this is what I did, not necessarily what you should do". My whole life is a lot like that, come to think of it.