Cross-posting this post on "abused lithium batteries" from the EVDL this
week.
It's from a thread on lithium battery life experienced by several users.
One user noted his 2007 Thundersky lithium pack that was only ever
discharged between 30-80% and didn't last but 500 cycles. Another noted
that the cycle life for these batteries is inversely proportional to
discharge (and perhaps charge) current levels, having noted that 0.5C
discharge rates were fine, but that the cycle life drops exponentially with
current such that at 1.4C discharge rates, the user measured less than a
500-cycle life and 16,000ah total energy delivered---presumably these were
40ah-80ah rated cells.
The post below points out that the cycle life risks of battery neglect do
not disappear when you switch from PbA batteries to lithium...
-----Original Message-----
From: ev-bounces@lists.sjsu.edu [mailto:ev-bounces@lists.sjsu.edu] On Behalf
Of Steve Clunn
Sent: Sunday, December 12, 2010 8:22 AM
To: ev@lists.sjsu.edu
Subject: [EVDL] Abused Lithium Batteries
I just a got a car in the shop that has 88 - 100ah( Foxx power bms)
lithium batteries ( they look like thunder sky) and I believe, fairly
new. It appears that the car had sat with the DC to DC converter
pumping the amp hours out of these batteries for a long time. The
voltages ranged from zero to 2.5V. The regulators that bolted on top
of the batteries will let the batteries charge up to 3.65V and then
come ON and drain the batteries down to 3.35V. I charged the pack up
carefully, and much to my surprise, all the batteries came up and sat
at 3.3V. After a discharge, I weeded out 5 of the worst ones and was
able to pull 45 ah out of the pack with a slow discharge over a 10
hour period, at which point Voltage was sitting around 3.0V. My
question is:..... what is the best way to try to get these batteries
back to the best of shape? Cycling them, etc. and if they have lost
1/2 of their capacitance, does this mean that they have lost 1/2 of
their cycle life? Or, is it like a lead acid battery that when you
have lost half of your capacitance, you really don't have any cycle
life at all?
One other note... I have an amp hour gauge that I am using (LinkPro)
and as it is set up for Lead Acid batteries, the meter is not reading
zero amp hours, but more along the line of Neg 4 ah after I completely
charge the batteries from their discharge test. I am assuming because
of the 10% overcharge that is required of lead acid batteries and that
this is figured into the meter set up. I bring this up, only to
illustrate that the batteries don't seem to be "leaking" any ah. As
electron containers, they seem pretty good.
Steve Clunn
--
Tomorrows Ride TODAY !
Visit our shop web page at: www.Greenshedconversions.com
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