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Terminal area & current capacity

Colonel.lp

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Jun 8, 2020
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This question has come up in relation to the welded studs that Chinese suppliers are shipping their Eve & Lischen cells with these days.

It would be great if those of you with more technical knowledge could expand on my limited research (googling)

The welded studs are reported to have a 10mm diameter, with an m6 stud.

Assuming a 6.7mm busbar or connector hole, the effective contact area is about 43mm²

Google tells me that maximum current density for aluminium ranges between 0.5A/mm² a few at 0.7A/mm2 with a couple of outliers saying 1 to 1.5A/mm²

So that gives me anywhere between 21.5Amps to 64.5amps.

Tables for aluminium wire show around 100amps(but I'm aware stranded cables can carry more current)

So what gives? Whichever way I look at this, the rating of these welded studs would appear to be shockingly low for batteries that are rated to supply 280amps.
 
I’ve seen no mention from you of bus bar thickness or terminal thickness. There is a width length and height associated with bus bars. The same is true of battery terminals. Perhaps this is a path of explanation?
 
I’ve seen no mention from you of bus bar thickness or terminal thickness. There is a width length and height associated with bus bars. The same is true of battery terminals. Perhaps this is a path of explanation?
I'm trying to asses the current capacity of the terminal face to busbar, not the busbar itself, thats the limiting factor.

It's no different to calculating busbar capacity, which is cross sectional area X ampacity(Current density)
 
I'm trying to asses the current capacity of the terminal face to busbar, not the busbar itself, thats the limiting factor.

It's no different to calculating busbar capacity, which is cross sectional area X ampacity(Current density)

Curious to see what you learn.
 
I wouldn't be surprised if the terminal current capacity is lower than a lot of peoples busbar current capacity.
If the terminal surface is not fit to cover the maximum continuous discharge rate then the doco should be amended.
 
Perhaps the heat generated from the loss is what shortens the battery lives at high c and d rates.
 
The busbar melted above where the terminal exploded. The busbar was still usable by turning it over.
The terminal was gone except for a small piece. The cell still checked normal voltage.
That was due to arcing and a dead short where there was no fuse, though. Yes? We all know the short power potential of these batteries is much more than 1 or 2 c.
 
That was due to arcing and a dead short where there was no fuse, though. Yes? We all know the short power potential of these batteries is much more than 1 or 2 c.
I'm not convinced that the busbar will melt before the terminal in any case.

edit: I shouldn't say any case. And 8 AWG wire would melt before the terminal.
 
I think in the presence of an explosive meltdown, all bets are off about any presumptions or assumptions. It will fail spectacularly different every time.

edit: unless....of course, you over engineer the hell out of it.
 
It’s a concern of two issues. Stud to battery, and bussbar to stud. on the bussbar there’s perfect world capacity with fresh aluminum, not oxidized and tight. With a bit of settling and lack of clamping pressure after a few thermal cycles, and maybe some oxidation, that’s just a resistor now.

The welded land area though, that would need torn off to measure contact area. its likely the bussbar is acting as a heatsink for it.

after seeing the video of a welding operation at lishen, I would guess on the side of it’s insufficient.

Im interested too see and hear what others think. Any thermal cameras out there?
 
This question has come up in relation to the welded studs that Chinese suppliers are shipping their Eve & Lischen cells with these days.

It would be great if those of you with more technical knowledge could expand on my limited research (googling)

The welded studs are reported to have a 10mm diameter, with an m6 stud.

Assuming a 6.7mm busbar or connector hole, the effective contact area is about 43mm²

Google tells me that maximum current density for aluminium ranges between 0.5A/mm² a few at 0.7A/mm2 with a couple of outliers saying 1 to 1.5A/mm²

So that gives me anywhere between 21.5Amps to 64.5amps.

Tables for aluminium wire show around 100amps(but I'm aware stranded cables can carry more current)

So what gives? Whichever way I look at this, the rating of these welded studs would appear to be shockingly low for batteries that are rated to supply 280amps.

The EVE 280Ah terminals are 18mm diameter (but only 16mm diameter at the top as far as contact area.

18mm diameter translates to 254.5mm^2 of cross-section and the terminals are about 10mm deep.

Resistivity of aluminum is 2.65 x 10^-8 Ohm x m or about 1.04 uOhms from bottom of terminal to top (ignoring the drilled hole).

If you put 300A or even 600A through that terminal, you’ll only drop 0.3 to 0.6mV and the heat generated within the terminal itself will be only 0.1 to 0.37W (immaterial).

So the aluminum terminal itself will be fine, even at sustained 2C discharge current.

The contact resistance between the aluminum surface and the welded ring as well as the resistance through the welded ring itself into the stainless platten may be another matter entirely and I believe that is where any attention should be focused...
 
The contact resistance between the aluminum surface and the welded ring as well as the resistance through the welded ring itself into the stainless platten may be another matter entirely and I believe that is where any attention should be focused...
Exactly, wherever the weakest link is, be it the terminal to stud weld, or the stud face to busbar.

Whichever way you look at it unless someone has some real world measurements, to me the welded studs look very inferior in terms of current capacity (ampacity or current density, whichever terminology you want to use). We have basically gone from a 18mm diameter contact face to a 10mm, that's huge.
 
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