Suspicious calb cell

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I've seen this a few times and not had any luck with warranting cells from
the company. One thing I have not seen mentioned that I believe might be
happening is that as these batteries get a little age on them and their
internal resistance goes up when they are charging their BMS starts
shunting current before everyone in the pack is charged and that one cell
starts to fall behind the others as the BMS shunts current which decreases
its amp hours in that cell. Which BMS are you using? I have wired another
cell in parallel with the offending stinker to fix the problem. Steve Clunn
with greenshedconvention.com
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Sounds reasonable, but surely the charge current is much less than the
discharge, so voltage drop on discharge will triggrer low charge cutoff
for the pack long before this becomes an issue with charging? I have had
problems with high self discharge on headway cells, still within spec of
5% per month, but even at 5% it is enough to cause serious problems when
others are zero, unless it is charged often.



On 08-Feb-18 3:26 AM, Steve Clunn via EV wrote:

> I've seen this a few times and not had any luck with warranting cells from
> the company. One thing I have not seen mentioned that I believe might be
> happening is that as these batteries get a little age on them and their
> internal resistance goes up when they are charging their BMS starts
> shunting current before everyone in the pack is charged and that one cell
> starts to fall behind the others as the BMS shunts current which decreases
> its amp hours in that cell. Which BMS are you using? I have wired another
> cell in parallel with the offending stinker to fix the problem. Steve Clunn
> with greenshedconvention.com
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George Tyler via EV wrote:
> Sounds reasonable, but surely the charge current is much less than the
> discharge, so voltage drop on discharge will triggrer low charge cutoff
> for the pack long before this becomes an issue with charging? I have had
> problems with high self discharge on headway cells, still within spec of
> 5% per month, but even at 5% it is enough to cause serious problems when
> others are zero, unless it is charged often.

I think it would depend on how close to the normal values the limits are
set. Maybe the over-voltage limit is only 0.1v above the normal
end-of-charge voltage, while the under-voltage limit is 1 volt below the
normal end-of-discharge voltage.

--
It is vanity to do with more that which can be done with less.
         -- William of Ockham
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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