[ausev] Help with EV calculations for 92 Ford Festiva

[Willie McKemie]

On Sat, Jun 13, 2009 at 09:01:08PM -0500, Lant Colburn wrote:
> I am in the middle of converting a 1992 Ford Festiva to all electric. I 
> have installed a D&D ES-31B 72-144 VDC 18hp motor mounted to the 
> original transaxle without a clutch. I have a new 144volt Kelly 
> controller. Originally my plan was to install 12 - 12volt 100Ah AGM 
> batteries, but with Lithium battery prices getting more reasonable, I am 
> thinking of using 37 Thunder Sky 3.8 volt 60Ah Lithium batteries in 
> single string. Each lithium battery weighs about 5.5lbs. My thought is 
> that  the  huge decrease in weight will go a long way to offsetting the 
> lower amp hour rating of the lithium pack.

Last month on EVDL, we had a long discussion on the topic of trying to 
minimize the cost of a lithium pack by sizing it to hold about the 
same energy as a lead pack.  You may find it here:
http://evdl.org/archive/
by searching on "battery opinion"; it started May 19.

Your pack of 37 60ah cells will hold 37 x 3.2 X 60 = 7104 watt-hours of 
energy.  Of that, only 70-80% is useable, around 5 KWH.  Your 
conversion will likely consume between 250 and 300 wh/mile at around 
50 mph; your range would be 15-25 miles.

The problem with using small cells is that you hammer them with high 
current draws.  That leads to not only voltage sag, but also shorter 
life.

There have been small cars converted to use 40-45 90ah cells but I have 
heard of none using smaller cells.  Here is a 45 x 90ah:
http://www.evalbum.com/1257

Personally, I would like to see results of small cell conversions, but 
I fear both poor performance and short life.  My conversion:
http://www.evalbum.com/2314
uses 45 260ah cells.  Current draws are very modest, well under 1C most 
of the time.  If I wanted a less expensive and shorter range pack, I 
would have no qualms about using 180ah-200ah cells.

Tests, rumors, and scuttlebutt leads us to believe that TS is testing 
and matching cells so that you will get at least advertised capacity 
from each cell.  My tests indicate that my 260ah cells actually hold 
more like 300ah.  Search on "TS-LFP260 pack capacity test" at the above 
archive URL.

LFP cells have about three times the energy density as lead.  It is 
difficult to configure a successful LFP pack to be 1/3 the weight of a 
lead pack.  I think you should shoot for at least 2/3 the weight of a 
lead pack and accept the blessings of double the range of a lead pack, 
much longer life, freedoom from maintenance, corrosion, and voltage 
sag.

-- 
Willie, ONWARD!  Through the fog!
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