# [EVDL] Best LiFePO4 Calb charging



## EVDL List (Jul 27, 2007)

My understanding is the CALB spec is charge to 3.6V at 0.05C charging
current, then end charge. The ending voltage of course will depend on
charging current level, since the V drop across the ir of cells will be
larger for higher charging currents. Jack R. did a demonstration of this
some time ago, and if you have regen, you can watch the pack get driven to
significantly higher voltage at 100A regen compared to 20A regen when
starting from about the same pack SOC. 

So there is a question as to what voltage you should charge to at charging
currents different than 0.05C, and how much this can vary without causing
any short or long term damage to cells. Let me be clear that I don't know
:^) My approach has been to charge cells to about 3.45V at constant current
around 0.05V, or to a lower voltage with lower current assuming linear
scaling, and then see how much charge (Ah) it takes to drive cells to 3.5V
after that. I then set up my Manzanita charger so that once it hits the
limit voltage and the timer starts, it adds no more than the above amount of
charge to the cells. I don't get much shunting action in this case (shunts
turn on at ~3.5 +/- 0.01V for my minibms bds), typically only the few that
have drifted/shifted sufficiently higher than the others that their shunts
turn on for a while. 

I think others regularly charge until all shunts are on, and may let the bms
HVC function (3.6V for minibms) shut off the charger, and I haven't seen
anyone report problems. I don't like to charge CALB cells that high, and I
wouldn't intentionally drive them to 4.0V, ever. Though I did drive a
couple to about 3.95V well over a year ago and they still seem to operate
the same as the others. Told you I didn't know :^).



> Mark wrote: "My charge current reduction switches over to a resistor to drop
> from 10 amps to 1.5A when any one of the balancers hits 3.6V and starts
> regulating (so it won't fry the regulators) seams to trip to low current
> mode at about 124-125V total."
> ...


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## EVDL List (Jul 27, 2007)

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## EVDL List (Jul 27, 2007)

It is likely that the early failures are the packs
where something is *seriously* out of whack or where
an owner continues to seriously overcharge or otherwise
abuse its cells - so with the reports here we can learn
and adjust our ways - until all packs are operated
within acceptable limits and get good longevity, then
either the calendar life will get it or the wear and
tear from daily cycling, high currents or temp extremes
will eventually cause failing cells or general deterioration
of the whole pack.

BTW, another reason for early failures are manufacturing
defects, apparently even in LiFePO4 packs those can have
disastrous effects, judging by the occasional fire even
with no BMS and no charging...

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 =


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behal=
f Of Evan Tuer
Sent: Thursday, March 29, 2012 1:33 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Best LiFePO4 Calb charging



> tomw <[email protected]> wrote:
> 
> >
> > Interested to see what other's experience is. It will likely be a =
> ...


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