---------- Forwarded message ----------
From: <donmc
...@pobox.com>
Date: Thu, Nov 5, 2009 at 7:54 PM
Subject: NBEAA November 2009 Newsletter
To: donmc
...@pobox.com
NBEAA Newsletter
November 3, 2009
www.nbeaa.org
Next NBEAA Meeting
------------------
Saturday, November 7, 2009, 10 AM to Noon
General Dynamics, 511 Grove Street, Healdburg. Note: this is a secure
facility.
You will be greeted at the entrance and escorted through the site.
NBEAA member Alan Soule will present his Tesla Roadster, then give rides!
NOTE: in the event of larger than normal attendance, Alan has agreed to
stay
after, continuing to give rides until he gets low on charge. But since some
people
may not be able to stay late, Chris Jones will have a clipboard and will be
taking
names of those interested in a ride along with the time of their arrival,
and Alan
will give rides in the order of arrival. Chris will arrive by 9:30 AM.
See Alan Soule's Tesla presentation at
http://www.nbeaa.org/meetings/SoulesTeslaNov09.pdf. See Tesla Motors'
website at
www.teslamotors.com.
Upcoming EV Classes in Sebastopol
---------------------------------
The Blue Sky Center in Sebastopol is hosting the following EV Classes:
MME 05: UNDERSTANDING ELECTRIC VEHICLES IN ONE DAY - 1 DAY, $150, next
class Jan. 15
MME 20: BUILD YOUR ELECTRIC MOTORCYCLE FROM OUR KIT - 2 DAYS, $300, next
class Nov. 5-6
MME 30: ELECTRIC VEHICLE CLINIC AND DESIGN CONCEPTS - 3 DAYS, $425, next
class Nov. 13-15
MME 50: ELECTRIC VEHICLE CONVERSION OR CONSTRUCTION - 5 DAYS, $795, next
class Jan. 18-22, 2010
MME 50- 2: ELECTRIC VEHICLE CONVERSION OR CONSTRUCTION - 5 DAYS, $795 Nov.
13-15 & Dec. 4-6
See http://www.makemineelectric.com/workshops.html for class descriptions
and
registration details.
Upcoming EV Battery Seminar in Santa Cruz
-----------------------------------------
Electro Automotive will be hosting a seminar about EV batteries Saturday
January 30th
2010 from 10 AM to 5:30 PM at the University Inn & Conference Center, 611
Ocean St.,
Santa Cruz. Jim Ramos of American Battery will speak on lead acid
batteries, then
Dr. Andrew Burke of the Institute of Transportation Studies at UC Davis will
speak
on lithium batteries, followed by Mike Brown of Electro Automotive who will
speak on
physical battery containment in the vehicle. Cost is $100. See
http://www.electroauto.com/batteryseminar.shtml for talk description and
registration
details.
Upcoming NBEAA Elections
------------------------
Do you want to learn more about EVs, advance the EV cause, serve your
fellow club
members and the general public, and have fun? Run for an NBEAA officer
position, or
volunteer for one of our apppointed positions for 2010! The more people
that get more
involved, the greater our progress and our enjoyment will be. Positions
include:
Elected Chapter Officers
President
Secretary
Treasurer
Public Relations Program Director
Meeting Program Director
Appointed Positions
Librarian
Webmaster
Newsletter Editor
Web Content Contributors (multiple positions)
More details are posted at http://www.nbeaa.org/about.htm. Please contact
Chris Jones
at chris_b_jo...@prodigy.net or (707)577-2391 if you would like to run for
office, or
be appointed to a position by November 30th. Ballots go out December 1 to
paid up club
members and are due December 31.
If you'd rather contribute one block of time such as contributing to a
single website
item or presenting an EV topic at a club meeting, please contact Chris as
well.
Electric Vehicle Safety Lesson from Toyota's Runaway Cars
---------------------------------------------------------
By Chris Jones, NBEAA President
An article in the Press Democrat on October 19th posted at
http://www.pressdemocrat.com/article/20091019/BUSINESS/910191027 describes
the Toyota recall for improper floor mat installation that can cause the
accelerator to stick on.
One local Prius owner reports that it is that they are anchored down so well
that they
are hard to reinstall after cleaning, so such a failure on a mass produced
car is
understandable. Another local owner heard on the news that there might be
an
intermittent firmware bug that could be causing this problem as well.
The interesting detail given is that some of their cars, including the
Prius, do not have
a traditional key ignition switch; instead, they have a combination of a
wireless key and
a power button on the dash. The little known fact is that it takes 3
seconds of pressing
the power button while in motion to stop the motor. This is similar to
holding down a
personal computer's power button for 5 seconds to shut off before the
operating system
has time to complete saving system files to the hard drive. Although this
three second
feature is written in the manual, unfortunately some of the drivers may not
have known
that, or remembered it under pressure, and at least 5 people have died from
this.
A detail notably absent from the article is that another way to depower the
vehicle is to
put it in neutral. A local Prius owner tried this, and indeed the car
depowered
gracefully, compared to when he pressed the power button for three seconds
and the car
depowered but was left in a hung state. He reports that the neutral switch
feels more like
an electronic switch rather than a lever that mechanically disables the
drive line, so if
there is an intermittent firmware bug, switching in to neutral may not work,
depending
on how the switch connects with the control system, and the nature of the
bug.
Obviously, if you drive a Prius or other Toyota without a standard ignition
key, or know
someone who does, make sure to get the floor mat recall service done on the
vehicle, if
applicable. And remember that if the car does get stuck on, try neutral,
then press the
power button for 3 seconds. But since 3 seconds could be too late, a future
Toyota
recall may be a firmware revision to shorten that time.
Many of us in the EV community are driving, building or designing EVs with
far less
engineering and testing put in to them than what Toyota has done. Some EV
conversions lack adequate power cutoff ability redundancy. This is
particularly dangerous in DC
conversions, where a common failure mode is where the motor controller
transistors short
on. This draws hundreds to thousands of amps out of the batteries for a
fraction of a
second depending on their size, chemistry and construction. Regardless of
battery, the
current surge will probably last long enough and followed by a high enough
continuous
current to weld the main contactor shut, rendering the ignition key shutoff
process
useless. Adding a second contactor in series will not help eliminate this
failure mode,
since it will see the same current. Adding them in parallel may not work if
they are not
the exact same resistance and don't open at the same time, welding the lower
resistance
or lagging contactor shut.
Having fuses in each battery compartment is a must. But depending on the
battery, the
fuse, and the resistance of the short, it could take seconds to blow, which
again may be
too late. Fortunately, most DC conversion drivers use small, low RPM motors
in heavy
vehicles and hence retain the clutch to ease the shifting of gears of a
manual transmission
to maintain optimum performance and efficiency, providing a reliable backup
mechanical power disconnect. This is a good thing, since we tend to
overwork these motors, most of which were designed for heavy but low speed
fork lifts. Unfortunately, excess current drawn under heavy acceleration and
low RPM that leads to overheating, shorting transistors and the on failure
mode doesn't make any noise, except in a Curtis 1231C DC motor controller.
By all means, if you have a Curtis 1231C and regularly hear the 1.5 kHz
whine at high loads telling you that your motor is in cutback mode due to
overheating, do something to reduce your current draw without overrevving
your motor. RPM and motor current gages help, but the former are rare
except for at least Cafe Electric Zilla, and safe isolated versions of the
latter that keep high voltage out of the cab are similarly rare and can be
expensive.
Conversions with shiftable transmissions but no clutch may not disengage
under the extreme
torque that a DC motor can provide -- the added torque can add friction to
the disengagement of the gears from each other, and they were not designed
to be disengaged that way. Testing for this could be dangerous, as well as
destructive.
Adding a circuit breaker near the motor controller with a very robust
remote cable actuator
within reach of the driver in the cab might be an adequate shutoff, but it
needs to exceed
the short circuit current of the batteries. For example, Heinemann has
models that break
10,000 amps at 160V DC, but some of the Airpax models only break 1600 amps.
The latter may be enough for most batteries, but large packs of the lower
internal resistance batteries
such as high power AGMs and LiFePO4s may put out far more than this, as well
as
ultracapacitors. You can estimate the short circuit current from Ohm's Law,
dividing the pack
rest voltage by the internal resistance, but this is only a ball park.
Contact me at
www.nbeaa.org if you have any questions about this calculation, where to get
the internal
resistance data, or how to estimate it by taking voltage and current
measurements under load. When in doubt, add robust redundancy such as a
clutch, or another electrical cutoff mechanism that is rated to stop your
battery pack safely.
Having a watchdog circuit that monitors battery current and disables the
main contactor when
it exceeds a threshold is a nice feature, and helps reduce risk. The Zilla
motor controllers
advertise this feature. But electronics can fail, and a circuit like this
is difficult to
test, unlike say lighting a warning light for a second while starting a
vehicle to make sure
it isn't burned out.
AC drive systems are less prone to this type of failure, since shorting on
would provide a
static magnetic field which would stop an AC motor. The AC control system
could fail in an
on state, but it may not go above the maximum rating of the motor controller
which may not
weld the contactor shut. And it may have a battery current watchdog circuit
as described
above. But the risk is still there, and many AC conversions with higher RPM
rated motors
and higher efficiencies have a fixed gear transaxle and no clutch. This
offers elegance and
light weight, but no mechanical cutoff, not to mention potentially decreased
performance. I
personally believe that AC drive systems should have some form of robust
cutoff redundancy.
Fortunately the only direct experience I have with a car accelerator
sticking on was when my
1966 Mustang was still gas powered, and my incorrect rebuild of the
carburetor led to a rod
popping out of its housing which wedged the butterfly valve wide open.
Fortunately my wife
and I survived because the robust cutoff system, the keyed ignition switch,
stopped the car,
and my mere 120 HP 200 six cylinder at altitude in Colorado gave me enough
time to react.
But we were driving on a curvy highway at high speed, so it was scary for a
brief moment.
So combined with the fact that I am not a professional automotive engineer,
the above is all
speculation. But please do be careful with any vehicle you are involved
with in any way.
If you have any questions, or comments to add to this discussion, please
contact me per
above. We need to share information to help each other further the progress
of EVs without
unnecessarily jeopardizing anyone's safety. This article has already been
greatly
improved after getting feedback from Prius drivers.
--
EV: choose to e-volve...
love ... forgive ... release ... bless
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