Thanks everyone for the thoughtful replies. I'm very hopeful that the
problem is something external that I have control over, rather than
internal, which I don't. I'll be putting lots of attention into that
terminal, strap and hardware tomorrow. It will be embarrassing if it
turns out to be something simple. I did withhold some information,
which is that I swapped out the BMS card on that cell, and the one
immediately to the right (in the "front/composite image") after the
balancing. Could be that I missed torquing the bolt on that one,
although it should be very snug even without the click wrench applied.
The battery in the conversion truck I bought had been cared for in
terms of loading and balancing, and had a PFC-20 with conservative
settings, but the installation was somewhat careless, no
anti-corrosion compound on anything, lots of tarnished terminals and
straps, corrosion, arcing on cell terminals, odd bits of bent-up
copper being used as conductors between sub packs and fuses, shunts,
etc. The whole thing had been exposed to under-hood water splash,
salt-air/costal marine environment, road dirt, etc, etc.
I did a meticulous clean-up, restoration, and installation, filing
the cell terminals flat when needed, digging out arced pit spots in
the terminals (very hard metal compounds produced there, couldn't be
simply filed away). All of the straps were flattened and filed when
needed. The cell terminals and strap ends were random-orbital sanded
with two grades of Scotchbrite abrasive discs, and NoOxID (my
preference instead of NoAlOx) applied immediately afterwards (yes, I
am aware how quickly aluminum oxidizes, but I have to work with what
I got. Remember that only the positive cell terminals are aluminum,
the negs are copper.)
As for having a "proper BMS", well, sure, but I'm a little stuck on
the cost, being almost twice what I paid for the whole conversion
truck, complete with battery, Warp 11, PFC-20, Zilla 1K, etc. This
was an economy Li conversion for me, and since the cells were nearly
free, well, you get the idea... (if anyone is looking for a motor,
controller, HEPA pedal, contact me off-list, I'd like to reclaim some
more of my garage floor).
Details tomorrow after the tear-down. I may have access to the IR
camera again next week, although now that I have pinpointed the warm
cell, it's possible to do a rough investigation by simply touching.
The jumper straps on all of the other cells were dead-cold, while
this one was slightly warm to the touch.
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