Hello David
The statement by Jack as I recall was this.
That LiFePo4 cells resistance, because it is so low, resistance is no
longer relevant.
I very strongly disagree. I believe the lower the battery resistance,
it
can even cause a greater the impact. While resistance readings on
LiFePo4
cells, is much lower then many other chemistries, battery resistance is
always relevant.
I have been measuring resistance readings for years and consider it
critical information.
Under a load, cells with less resistance hold a higher voltage. During
charging, the cells with lower resistance will have a lower voltage. This
is
nothing new and known by almost everyone on this list.
Energy moves in and out of LiFePo4 with far less resistance. Since
LiFePo4
can have up to 1/20 resistance or even less compared to new lead or NiMH
battery. At first take it would seem reasonable to assume with
resistance
being so low, its just that much less of a factor over prior battery
chemistries.
Seems logical at first, lower resistance should mean less loss of energy
to heat in the battery, so this should have all around less impact.
However there is an error, in assuming with these very low loses,
resistance is no longer anymore a concern. As good as the CALB cells
are,
the
resistance readings do vary. When you compare cell to cell, in a pack of
50 or
100 cells of LiFePo4, between the lowest and highest resistance can be
almost 100% off from one another. Since cells are being charged in
series, these
losses as small as they are, impact the amount of the energy remaining
in
each cell.
Over time these small differences change the SOC of the cells, and throw
the pack out of balance. If you have 100% differences in resistance
readings
in a lead or NiMH pack it would quickly become a noticeable problem.
Just
because it may not be immediately noticeable, does not mean that slight
differences no longer have an impact.
The CALB cells come with test sheets showing both capacity and resistance
readings. Overseeing these group buys I have looked at many thousands of
the CALB CA gray cells. Compared to lead or NiMH yes they are extremely
low.
I believe the CALB cells are the best value for the money.
If resistance readings were all exactly the same when new, and during
service then none of the above would apply. However in the real world
where
nothing is perfect, any differences between cells used in series
regardless of
how minor will always lead to a pack becoming out of balance.
Your losses in moving energy both in and out is far less with LiFePo4,
but
compared cell to cell the percentage of difference is even greater then
lead or NiMH.
Resistance readings can change a lot with temperature, SOC and cycle
life.
Resistance readings are very useful information. However they can be
frustrating at times because its a moving target. If your assembling a
pack they
all have to be very close to the same SOC and temperature.
I don't claim to be an expert or know it all. However to say that
resistance is no longer a concern in batteries, shows a clear lack of
completely
understanding batteries and losses used in series.
David hope I gave enough context here to address your reply "makes my
statement not correct 100% of the time." I have tried to watch three of
Jack's
Video's and three times he made a comment that I could hardly believe he
said. This resistance statement just happen to be the last one I tried to
watch. I appreciate Jack's or anyone else's testing batteries. However it
would be better to keep random thoughts not based on real data out of
them.
There is so much misinformation around in general about electric
vehicles
and its not just EVTV. Its sad to have someone misinform others looking
to
learn about EVs. I have tried to watched three of Jack's video's and
each
time he made a comment that was ridiculous. I don't think I have made it
more then half way through before I could no longer listen to nonsense
ramblings.
Don Blazer
In a message dated 6/13/2013 7:38:22 A.M. Pacific Daylight Time,
[email protected] writes:
Message: 7
Date: Wed, 12 Jun 2013 22:38:50 -0700
From: David Nelson <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Subject: Re: [EVDL] Jack Rickard of EVTV.me was 100ah pack on the
cheap
Message-ID:
<calxn3-i_oex_ejua8wwvh95zlqlqhyh-yzq_vf9hubsvj-q...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Don,
You gave no context to the statement you said that Jack said so that
makes
your statement also not correct 100% of the time. Depending on the
context,
resistance in an electrical circuit/system may or may not be a factor.
I know what you mean about lack of sufficient support for some of Jack's
statements. Like I said, however, many of them which apparently had not
enough basis have over several weeks/months/years been finally supported
but I would expect that a significant number of people miss it and then
just write off practically everything he says.
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