Watched the test on the video. In the end, he states "Four of the cells
were toast." at the end of the test. These were the cells that were
_not_ protected by the BMS. This looks like the BMS did its job quite
well and the test showed what was expected.
I guess you can interpret results in whatever way fits your theory, but
when the unprotected cells were "toast" then you really have to stretch
your interpretation beyond the limits of credibility.
There were folks right here on this list that performed a _scientific_
test. They cycled cells to find their capacity, charged the cells fully,
then placed them in storage. After extended time on the shelf, they
tested the state of charge by repeating the cycle once more to
ambivalently determine the state of charge and capacity once again. They
found, scientifically, there was indeed self discharge.
The peer reviewed literature agrees with the scientific tests that
Lee Hart tried for himself. Also, the peer-reviewed literature also says
that self-discharge doubles with each 10 Celsius increase in temperature
(which is a classic Arrhenius relation, as everyone knows that has taken
a chemistry course at the college level.) We all know that the end cells
have a completely different thermal environment than the middle cells,
when placed in a multi-cell pack. The cell temperature varies, causing
self-discharge to vary in a documented non-linear fashion. The cells
gradually get out of balance when placed in service in a high-voltage
pack, even if they were manufactured equally and perfectly.
Do you understand the difference between "anecdotal evidence" and
"scientific test"? When you say "I measured the voltage and it was close
to the same" that is anecdotal evidence. While Lee Hart's experiment of
carefully measuring state of charge by cycling the cell before and after
storage was a scientific test.
I'm wondering, are you so certain of your "anecdotal evidence" that
you would be willing to pay for burned cars, garages, and perhaps homes
of the folks that choose to follow your advice? Be careful what you wish
for.
Bill D.
On 6/28/2015 6:25 AM, Paul Dove via EV wrote:
There were no parasitic loads on any particular cells. They were powered by the
whole string in Hardys test.
Sent from my iPhone
On Jun 27, 2015, at 10:34 PM, EVDL Administrator via EV <ev@lists.evdl.org>
wrote:
On 27 Jun 2015 at 15:29, Peter Gabrielsson via EV wrote:
He proved that putting parasitic loads on some cells in a series string
vill cause the string to go out of balance.
That's what you'd expect, no?
I see this less-than-ideal behavior in my Ping batteries, which are fitted
with an integrated BMS. I just recently learned that although the current
BMS they use draws its power from the entire battery, the older ones
(including mine) drew BMS power from the lowest 4 cells.
Thus my BMS will indeed tend to imbalance the battery, especially if it's
not cycled regularly. However, the BMS has a "charged" LED for each cell,
and the only time I see more than a few minutes from first LED to all 8 is
when I've let it sit for months between uses and charges, something I don't
really recommend.
BTW, I just checked the capacity on these batteries. They're 4 years old
and seem to be holding up pretty well. They're rated for 10ah; one is
producing 9.7ah and the other 10.0ah. This is to a 19.8v cutoff (just
slightly less than 2.5vpc average).
David Roden - Akron, Ohio, USA
EVDL Administrator
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