Cross posting from the EV Discussion list since both lists asking battery
longevity issues...some considerations you should be aware of if you are
going with Lithium chemistries...
In my case, I'm still running with 6 used T105's...$20 each. These only are
delivering about 80ah of usable capacity at about 50amps drain, but can't
beat the price---been at least a couple years now with these. My earlier
set of 12 T-105's were already old when I started with them and with ages
between 8- and 10-years, I migrated them to my antique electric car 2yrs ago
and they still give about 16-20-mile range as a 10-yr+ aged pack.
I do hope to one day get beyond lead though...:-)
-Myles Twete
www.evalbum.com/492
-----Original Message-----
From: ev-bounces@lists.sjsu.edu [mailto:ev-bounces@lists.sjsu.edu] On Behalf
Of Lee Hart
Sent: Saturday, June 25, 2011 9:44 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] How often should I charge Lifespan batteries for best
life?
A big problem is that no one has done careful testing to find out what
the relationship is between life and depth of discharge, charge and
discharge current, temperature, age, etc. The batteries are too new,
the testing is expensive and time consuming; so no one wants to do it.
It's easier to do brief accelerated life tests, make assumptions, depend
on anecdotes, or lie.
Judging from the behavior of older lithium cells that we *do* have life
data on:
- The higher the temperature, the shorter the life. The effect is
large; on the order of half the life for every 10 deg.C increase
in temperature.
- The higher the state of charge, the shorter the life. The effect
appears to be exponential; little difference between 50-80%, a
small difference between 80-90%, a big difference between 90-100%,
and almost immediate failure between 100-110%.
- The deeper the discharge, the shorter the life. For example,
life at 40% DOD may be 4 times longer than at 80% DOD (twice
the total amphours over life). There is probably an optimum
depth of discharge to get the maximum total amphours over
life; but it hasn't been determined.
- The effect of current is not clear, until it gets large enough
to cause a temperature increase. It may be that the current itself
isn't the cause, but rather the temperature that shortens life.
A big problem is that the chemistry keeps changing. What was true for
last year's design may not be true for this year's design.
Another big problem is that quality control problems, ignorance,
negligence, and abuse are more likely to determine the life than the
actual nature of the cells. In other words, the cells are more likely to
be murdered than to die of old age.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
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