So good to read that you found it was caused by being simply forgetful. I go
over all the terminals two or three times as it is so easy to miss one in a
couple of hundred.
Previous posts mentioned using Noalox paste. I used to use it as advised on
various forums but have been burning out the odd Orion BMS inputs over the past
few years on my two home builds.For the recent rebuild of the traction battery
and again repaired BMS I cleaned up the connections with wire wool and alcohol.
You could see on the links where the contact had been poor and I suppose caused
a rise in voltage across the sensing circuit.They have been faultless since.
It is possible that the Noalox had become separated in the bottle but as a long
term industrial electrician who has never used the stuff before, I decided to
use the tried and tested method of having bright clean (tight) connections.
On Thursday, 3 October 2019, 00:19:03 BST, Mr. Sharkey via EV
<[email protected]> wrote:
Well, it looks like this issue may have been one of my own making.
When I went to remove the cell interconnect strap, both bolts into
the cell terminals were "just snug", not tight. Apparently I got
distracted when completing the BMS card swap, and didn't torque the bolts.
The straps are made up of four .025" "leaves" of copper stock, with a
little hickey bend in the center for mechanical relief between the
cells. A sleeve of heat shrink tubing protects the center of the
completed strap, and holds it together for assembly on the pack. This
was one that I had disassembled to repair, probably because it had
been intentionally bent by the previous owner to do something that it
wasn't intended to do.
When I took it off, it didn't look at all unusual on the top, and the
bottom looked fine, it had been in complete contact with the cell
terminals by the appearance of the anti-corrosion grease.
Inside was a different matter. I cut the heat shrink off and found this:
http://www.westlanetv.org/~sharkey/evgfx/Hot_Strap.jpg
The four leaves from right-to-left are top-to-bottom, respectively,
and the bottom of the photo is the end that was connected to the
too-warm cell in the IR photo.
I wish I had been able to use some brand name green abrasive pads
instead of the dollar-store pretend ones, cleaning the discoloration
out of the straps would have been much easier. Afterwards, I hit them
with real white Scotchbrite, then gave them a shine with Brasso for
good measure. A wash with denatured alcohol, and I put them back on
the cells. I'm going to go all over the battery and check all the
fasteners for proper torque before putting the cover back on the pack.
In the long term, I think I might build a new strap. If this one was
so abused that I needed to take it apart to use it again, there may
be some issues with the leaves not making as complete of a contact
with each other as new, flat straps made from new stock. I don't have
any .025 stock, so I use five leaves of .020 copper to build new straps.
I hope to have another session with the IR camera next week to see if
my efforts to correct this little screw-up have been successful.
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