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RE: (ET) batteries
I agree with David Roden. In the HEV industry we try to keep the pack State
of Charge (SOC) between 40% and 80% but that is for the hybrid vehicles.
For the battery vehicle most design the system to indicate empty at a SOC
of 20% or 80% Depth of Discharge (DOD). A little tidbit sometimes the SOC
is also called the State of Health (SOH).
This is a little off the subject but might interest a few people out there.
One of the harder task so far in engineering is accurately determining the
real SOC of the battery pack during pack usage. I just recently attended a
conference on the west coast and Toyota was reporting their analysis of a
fleet of RAV4 EV's used by California Edison. They are finding out that
their new battery management system is actually working better than
expected. Toyota indicated that they only expected 75K miles out of their
battery packs but they are seeing 100K and 120K presently. maybe someday
this technology will be scaled down to the lower voltage applications like
36V. I guess Toyota is very pleased with the results. They only originally
built 500 vehicles and then withdrew from the market. After talking to a
few others at Toyota there was a hint that they will be back producing EV's
again in the future. So they must have liked their findings. I also had a
chance to drive the RAV4 EV and Toyota's Fuel Cell vehicle while I was out
there and I have to say that they were so refined that it was hard to tell
that you were not driving a normal gas powered vehicle. The pickup, and
driveability was the best. The only difference was the very pleasing and
calming feel of the quiet powertrain systems. With the vehicle being so
quiet, when you stepped on the accelerator pedal the vehicle seemed to
effortlessly glide forward and up to speed. There is quite a difference
between the home brewed EV's we all have to make and refurbish comparing to
what the auto manufactures can produce if they put their minds to it.
Dave Reuter
"David Roden (Akron OH
USA)" <roden ald net> To:
elec-trak cosmos phy tufts edu
Sent by: cc:
elec-trak-bounces cosmos ph Subject: RE:
(ET) batteries
y.tufts.edu
02/17/2004 01:07 AM
On 15 Feb 2004 at 10:50, Travis Creswell wrote:
> I would suggest that you never let your pack voltage get under 33 volts
> under load.
Thie is pretty good advice. The usual rule of thumb is to consider an
under-
load voltage of 1.75 volts per cell (5.25 volts per module, or 31.5 volts
for
the pack) as fully discharged. Below that point you risk cell reversal. A
little "headroom" isn't a bad idea, just as keeping your depth of discharge
to
80% or less gives much better cycle life.
David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea 36vdc
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
All we learn from history is history repeats.
-- Andrew Ratshin
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