DAY fourteen: Nov. 21th, 2008 - Saturday.
Day thirteen of the Santa Rosa Junior College Course -
DET-193. ELECTRIC VEHICLE CONVERSION.
Jim Kelly, Department chair and Machine shop teacher at at SRJC Joined us to audit the class. It was reported that Chris Jones wrote a grant for the school and won $25,000 from AAA through its "Greenlight Initiative". The grant is to build a car and write a "how-to" book that can be used by other Junior Colleges.
Battery Management Systems
The Need: See various Youtube battery failure videos and other sites such as: www.peakbattery.com test.
Case Study - Michelle's Toyota.Arrived with a wide variety of charges and need a total of some 70v over the entire pack. However this would mean that some of the batteries will get over charged, and some under charged
Methods of BMS
1. Shunt curent from charged cells to less charged. - complicated and many wires passing around cells.
2. Shunt current from charged to cells to heat. Slight waste of powe, but if all cells are controlled then from teh get-go (unlike Michelles wild variations) then this is not a problem.
3. Charge each cells individually - complicated wiring
4. Start with all cells "empty" - charge in series until lowest capaciy cell is full - simple, but wastes capacity of the higher capacity batteries.
5. Charge all cells/batteries in parallel - requires some clever wiring and switching systems.
6. Manally check and charge each cell and battery - very labor intensive.
BMS should communicate with the Charging system
1. Totoal Pack State of Charge and State of Health
2. Individual Cell/Battery SOC and SOH
Other safety concerns
b. Increased internal resistance.
Methods and Ideal BMS - Too much to add here - I suggest you take the course, which in Spring 2009 will be Auto-193!
Needs to go back to Thunderstruck on Monday, we attempted to put it back together, but the class member who pulled it apart a couple of weeks ago wasn't there with her documentation and it didn't quite seem to fit together - so embarressingly we'll have to return it to Thunderstruck as is for them to put back together.
Electric Powered wheel chair
The melted plug is to be replaced by a clever set of connectors that fit together like leggo. The old melted plug and broken connection was worked on but we didn't get a status report at the end of the day.
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Electric Fork lift
Seems like nobody is too interest in working on this nasty old bit of equipment
Yamaha Mini-Enduro C.1980 .
The Battery Box (BB) was mounted and plans for the mounting of the controller undertaken. The final location decided on was the one suggested by our seven year old mentor Trever Jones.
Don's car (1982 Plymouth Horizon):
Work continued on fabricating the rear battery box, and the frame into which it will sit. The designe will allow the entire box of 20 cells to be dropped out through the bottom and removed on a floor jack for ease of access. Mountings for the front battery box were worked on. Low Voltat wiring on the component board was deemed complete - almost ready for installation.
Woody was boxed ready for removal. In my humble opinion, this was one of the better projects from a theoretical view point as it forced the group to think only about EV components. Working on the older cars has involved enormous effort in non EV repairs. I'd recommend that more effort be put on doing this in the class for the first few weeks. Then the latter part of the course could be more focused on the theory of Battery managment followed by trouble shooting and repair of EV problems (like Michelles Toyota).
Ed's Car (VW Cabriolet)
Reported to be a bit of a frustrating day, especially as the rear BB holddown mountings are proving problematic. However the main revers, power selector consul was installed, and other wiring under the dash and hood dealt with.
Team Harley :
Appears to have been abondoned as no Harley Team members have turned up for many weeks and the bike sits stripped and forlorne - another dream dead?
Batteris sag badly. Peter guided the class to think about why this could be, and with his prompting came to the conclusion that 1 or more batteries could be weak. So the batteries to be tested again for internal reistance and Numbers 13, and 6 were removed and replaced with Spare #1 (S1)and the old #8 [which had been all ready replaced by Spare #2 (S2) since it is in the most difficult location and we didn't want to have to every removed it again]. Even to replace # 6, #'s 1- 3 all had to be disconnected and removed - a fiddly task.
Once all in, the car was taken for another run, with 213V at the start, and battery sag was improved, not going below 178v. The car maintained 60 mph on the first half of the run, but when pulling off the freeway after 6 miles to head back, the mystery complete power outage noted last week re-occured, and again toggling the regen switch brought it back online. On the return trip with the pack at 200v, the top speed came down to 57mph. Again the mystery power outaged hit as we got off the Freeway close to the college but this time did not restart, and the car was ignomiously pushed back into the workshop to be diagnosed the week after Thanksgiving.