Re: Battery Cycle Life/Cost

["M.C. Appleby" <appleman@aztec.asu.edu>]

You have your trip energy consumption down to a science.   Presuming your
trips are daily (back to back) - why would you not recharge every two days
or possibly every three days?  It sounds like even every two days you would
only be at 50% SOC, but you would have doubled your cycles.




----- Original Message -----
From: "Mike Chancey" <evtinker@evalbum.com>
To: <ev@listproc.sjsu.edu>
Sent: Saturday, January 26, 2002 10:12 PM
Subject: Battery Cycle Life/Cost


> Hi folks,
>
> I have been wrestling with long term battery life issues,  trying to come
> up with an affordable way to get my Civic back into regular daily commuter
> use.  Unfortunately, all I am really discovering is this was the kind of
> analysis I probably should have done before building the car in the first
> place.  Here is what I came up with:
>
> My commute is roughly 25 miles round trip, but charging is usually
> available at work.  On weekends I probably put about 20 miles on each day,
> mostly in little 5 or 10 mile hops, so we are looking at about 165 miles
> per week, or about 8580 miles per year.  Assuming I recharge once at work
> and once at home every workday, and at least two charges per day on
> weekends, that is about 728 cycles per year.  Considering the current
power
> consumption of my Civic, roughly 350 watt hours/ mile due to hills and
> heater use, the 12.5 miles of each workday commute leg uses about 28% of a
> charge.  So, the battery pack is asked to deliver about 728 cycles at 28%
> depth of discharge.  The question is, how many cycles can I expect the
> batteries to deliver before failure?
>
> Currently, I have the Civic equipped with a set of 13 used Dynasty group
31
> AGMs (12 volt 100AH).  Due to numerous failures, I have discovered a $20
> used battery probably really isn't cheap after all.  Before I even
consider
> investing in 13 new ones though, I feel it might be wise to look at the
> chances of them lasting 1 year under my service demands.  I suspect there
> is little chance of getting a year out of them at all.  If they did last 1
> year, at roughly $1700 a set, my 8600 miles is going to cost about 20
cents
> per mile just for battery replacement cost.  Ouch.  Another alternative
> must be found.
>
> It just might be possible to rebuild the Civic to use 18 8-volt Trojan
> T-875 flooded batteries, though this would really ruin some of the car's
> best features.  Now we are looking at a battery cost of about $1200 per
> set, but due to the greater capacity, the cycle depth would only be about
> 20%.  For those who have used the T-875, what is the likely cycle life at
> 20% discharge?  I am guessing it might be possible to get at least 2 years
> out of them at this shallow cycle, 1456 cycles, or maybe that is too
> optimistic.  If they would last that long, then the battery cost would be
> down to about 7 cents per mile, quite a bit more reasonable.
>
> Taking this further, dropping down to 18 T-105s would make for pretty lame
> performance, (from 156 volts to 108) but that would increase capacity and
> reduce the cycle depth still further, to around 18%.  Battery pack cost
> would drop to about $900, or 10 cents per mile for 1 year of life, 5 cents
> per mile if they last for 2 years of service.
>
> At this point we are getting so far away from the existing conversion I
> would probably be better off to buy/build/trade for an EV designed for
> these more cost effective battery choices.  A 120-144 volt, T-105 equipped
> pickup would probably be a more appropriate choice for this commute I
guess.
>
> So, what kind of words of wisdom can you folks share with me?  Is there a
> better alternative?
>
> Thanks,
>
> Mike Chancey,
> '88 Civic EV
> Kansas City, Missouri
> EV List Photo Album at: http://evalbum.com
> My Electric Car at: http://www.geocities.com/electric_honda
> Mid-America EAA chapter at: http://maeaa.org
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>
>
>