I agree with Marco that it is quite likely a dirty/corroded connection
between the strap and the cell. This is more common than most folks realize.
Remove the strap. Clean both surfaces with Scotchbright. Apply a thin
coating of NoAlOx to the terminal and to the bus bar. Reassemble.
You shouldn't wait too long between the cleaning step and the reassembly
step. These should be done in the same work session as corrosion will
form on the freshly cleaned surface.
My two cents.
Bill D.
On 10/1/2019 7:09 PM, Ing. Marco Gaxiola via EV wrote:
Are you sure it is an internal cell failure and not just a loose or dirty
connection within the bussbar? The heat on that image looks only on one area
from the whole cell. Keep in mind that those ‘prismatic’ cells comes on tens or
hundreds of thin rectangular layers with the same shape of the plastic
enclosure. And a high internal resistance developed in cell chemistry would
probably show up an evenly hot across the enclusure. (Please correct me of
wrong).
Why don’t you try first to check for a poor electrical contact at that spot,
clean it, re-tighten it and repeat your test?
Marco Gaxiola
Sent from my iPhone
On Sep 30, 2019, at 8:57 PM, Mr. Sharkey via EV <ev@lists.evdl.org> wrote:
Time to turn up the dial on the technical channel.
After converting my car to a lightly-used set of Thundersky 160's, I've finally
gotten around to having some thermal images taken of the cells after running
the car up to temperature. My purpose was to make sure that none of my cell
interconnect wiring (copper strap stock) was heating up. What I found was
somewhat unexpected. One of the 38 cells was showing an elevated temperature
from the rest.
First, the IR image of the right-hand half of the pack, taken from behind the
car. the suspect cell is at the center cross-hairs:
http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg
A close-up of the cell, looking from the front of the pack. It's been
photoshopped to blend the IR image with the visible image to provide some
perspective of the actual appearance:
http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes most of
the way. A couple of 275 - 300 amp sprints pulling out into traffic, etc.
Photos were taken immediately thereafter.
All of the cells had been carefully (manually) balanced a few days before the
photos were taken. During balancing, this cell was about 15 ampere-hours lower
than most of the rest of the pack, but not the lowest of the 8 cells that
needed attention. It came right up with a balancing charge. None of the other
cells showed any variance in temperature in this series of photos.
Questions for the list:
The cell isn't actually "hot" but it's obviously warmer than the rest. What's
everyone's take on this one cell warming up? Can I just assume that it may have higher
internal resistance, and therefore more heating under load? Is the heating indicative of
a coming (perhaps spectacular) failure?
I've got about 1,600 miles on this new pack, and it seems to be performing
well. I'd like to keep using it in this configuration, but if it seems risky to
continue loading this one cell, it ~could~ be jumpered out of the pack (not my
first choice).
Opinions or advice?
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