NBEAA Newsletter November 3, 2009 www.nbeaa.org REVISED NOVEMBER 4 TO ADD DETAIL ABOUT THE PRIUS RECALL IN THE LAST ARTICLE. FURTHER REVISED MARCH 10 2010 TO CLARIFY THAT THE POWER SWITCH OR NEUTRAL MAY NOT STOP A PRIUS AT HIGHER SPEEDS. 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_jones@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 UPDATED MARCH 10 2010 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. But the difference is there is a standard that helps assure all computers shut down this way regardless of conditions; different cars may be designed to react differently. Although this three second feature is written in the Toyota manual and is posted on their recall FAQ web page at http://pressroom.toyota.com/pr/tms/customer-faqs-regarding-the-sticking-153495.aspx, unfortunately some of the drivers may not have known that, or remembered it under pressure, or it may not have worked during a defective event, and at least 5 people have died from this. A detail notably absent from the article is that another way to depower the vehicle may be to put it in neutral. A local Prius owner tried this at low speed, 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 without power steering or power brakes and and he had to pull over to restart it. 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. And as with the power switch, it may not work during a defective event. And per the recall FAQ mentioned above, Toyota infers that shifting in to neutral may not work. Obviously, if you drive a Prius or other Toyota without a standard ignition key, or know someone who does, make sure to get all recall services done on the vehicle, if applicable. And read the manual to or discuss with Toyota how to stop the vehicle if the accelerator does get stuck. 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.