Re: Battery Cycle Life/Cost

[Seth <sethea@mediaone.net>]

Doing this is very bad for the PbA batteries. 

Deeper discrages and leaving them less than fully charged, even for a
day, are two great ways to kill PbA batteries faster.

-Seth


"M.C. Appleby" wrote:
> 
> 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
> > Join the EV List at: http://www.madkatz.com/ev/evlist.html
> >
> >
> >