Tuesday, January 10, 2006
As I look at all the stuff necessary to convert this car to electric power, I'm coming to realize that a lot of the existing parts available are sub-optimal. Like most things in a market economy, they are more of a result of who can make money making what than parts that coherently fit together as a whole. What would be ideal would be some kind of magic box that would integrate AC motor control, battery charging, a 12VDC power supply, and an optional fluid heater into one enclosure. AC Propulsion's AC-150 system comes close. It integrates a first-rate AC motor controller with a high-power charger (with excellent power factor) by recycling the magnetics and electronics of the drive system, and it integrates the DC/DC converter. It is also designed to integrate cleanly with a vehicle that wasn't originally designed to be electrically powered. But the system also has its shortcomings: it is far too expensive (at US$25,000) for an EV hobbyist, the enclosure is too bulky to integrate cleanly in many donor cars, and the minimum nominal battery voltage is too high for a lightly-modified vehicle. It seems to me, however, that these shortcomings can be addressed, primarily by reducing the power level. A hundred and fifty kilowatts may make for good publicity, but most people don't expect that kind of power from their vehicle, particularly given the phenomenal torque characteristics of an AC system. An "AC-75" would be a much more practical system for everyday use. The second change I would make would be to water cooling (in fact, nearly everyone without Alan Cocconi's rumored chip on his shoulder would probably make the same change :). While you can argue that an air-cooled system is simpler, smaller, lighter and cheaper, a suitable heat-rejection system is already installed in nearly every conversion donor car, and water cooling makes the packaging of the motor and electronics much simpler. So I'd replace the two large heat sinks and fans with cold plates, some hose, and a small pump. Finally, the minimum 336 volts are simply too many. Depending on battery chemistry, it's either too much weight, too much cost, or both , although this may change as lithium battery chemistries mature (at 3.6 volts per cell and with their excellent weight characteristics, both the cell count and weight could be reasonable). If the minimum nominal voltage were roughly half that, it would be much more accessible for people using mid-priced batteries like Optimas. I don't know enough about their Reductive™ charging topology, but lowering the voltage to 180 or so should still allow charging from a 120V source. Alternatively one could go the route Toyota has gone with their newer hybrid systems and create a bi-directional DC/DC converter to raise the voltage that's practical for batteries to one that's practical for motor control. But the cost would probably be hard to justify at hobbyist EV volumes. Another place to save money would be on the RPM range, since most donor vehicles retain the original transmission. Shrinking the torque/speed range to something resembling that of an internal combustion engine could provide some opportunities for further cost savings. One side advantage of such a system is that there is exactly one termination point for the high-voltage wiring: the magic box. The only exception would be a resistance heater, but it may be possible to integrate that with the water cooling (with Peltier devices or a bigger cold plate enhancing the heat rejection of the electronics) so that a fluid heater could built into the unit. In the end, the cost for the combo would have to be about $5,000 at retail. Without a large market to recover the NRE costs, it's probably not economically feasible. But maybe some sort of open-source-style development process could bootstrap things, especially if it was a BSD-style license that allowed commercial interests to embrace and extend it.  I can understand why AC Propulsion is reluctant to produce such a beast: there's not a lot of money to be made in EV conversions, and at that power level they would be competing directly with DC systems that can advertise better performance.  If you're optimizing the cost and performance of the motor/drivetrain pair, this is probably pretty close to the optimum. But if you're optimizing for run-of-the-mill donor cars, this is at least twice as high as is practical.
What I've Got
One of the motivating factors for doing the electric conversion is that I already have a collection of EV parts that I can use for this project: a motor, controller, charger, DC/DC converter, and a bunch of battery interconnects and 2/0 welding cable to tie it all together. The motor is an 8-inch-diameter 100-pound beast. It is a series-wound DC motor made by Advanced DC and given model number XP-1263A. It is an experimental higher-voltage rewind of their workhorse 2003-06-4001A 8-inch motor, and to the best of my knowledge is no longer in production. The "A" indicates that it incorporates a tail shaft. The controller is the Curtis PMC 1231C-8601 "Whiner" (so called because it cuts back the switching frequency at low power to a very audible 1.5kHz). It will do 500 amps from a 96V to 144V (nominal) battery pack. The charger is a Zivan NG3 configured to charge a 144V pack of Optima Yellow-Top batteries from a 120V outlet. The DC/DC converter was designed for use in RVs to step down mains power to the 12V required by the battery-powered devices. It appears to be no longer available. If memory serves, it is a 30-amp unit that runs happily off a 144V battery pack. The interconnects are designed for creating series packs of batteries with standard SAE (automotive) posts. They work quite well and look very professional, although all that lead makes things a bit heavier than they need to be.
Monday, January 09, 2006
The project is going to go a little slow for a while. I have some other projects that need time, money, and attention that could otherwise be spent on the car, but currently are more important and/or urgent. My general course of action is going to be to complete the restoration first, and then launch into the electrification. Obviously in some cases this won't be practical, but it has a couple of advantages, not the least of which is that I can sell it as an ordinary VW project car should the need present itself. It will also give me a lot of time for the sort of head-scratching contemplation that goes into making a good electric conversion. In any case, the immediate next steps will be:
- Unbolt the fenders and re-attach them with the beading in place
- Reinstall the bumpers, headlights, taillights, turn signals, and the like
- Clean up the dashboard and install the gauges
- Reinstall the hood and trunk latches and the door handles
- A new windshield
- New window, door and trunk seals
- Interior parts
A Few Pictures
Thanks to my new camera phone, I now have a few pictures of the "body-in-blue" to show off. The combination of the CCD in the camera and the fluorescent lighting don't really do the color justice, and it's not helped by the lack of chrome, rubber, or glass to set off the color, but you get the idea.
Sunday, January 01, 2006
So what prompted me to decide to build an electric vehicle (EV) based on this car? Well it pretty much goes back to 1994, when I had just finished a rather difficult first year of college and I was really struggling with envisioning a future for myself that didn't suck. On the drive home I stopped at a friend's house in Palo Alto who had built an electric Volkswagen Rabbit from a kit a couple of years prior. The fact that you could make a useable electric car conversion was news to me. I had always pictured electric cars as being little boxy things not much faster than golf carts. But here was a perfectly useable (if a bit pokey) car that could do 30-40 miles of driving on a few dimes' worth of electricity. Even though things haven't quite turned out as I imagined, the experience gave me some direction in my education and future career that I had been sorely lacking. Over the summer I convinced my parents that they should fund my "educational experience" and help me out buying parts and a car to convert. I found a really crappy 1978 Honda Accord hatchback and proceeded to try and shoehorn eighteen 8-volt golf car batteries into the thing, along with an 8" diameter DC motor and the associated control and battery charging apparati. That first conversion is what could charitably be called a learning experience, or less charitably a series of important mistakes. But I'll save that list for its own post. After deciding that the Honda was just too much of a piece of crap to try and salvage, I decided to go for a more interesting donor car in better condition. I found a 1979 Porsche 924 and managed to get a pretty decent start on it before I left college and headed off to work. The experience of having a full time job in a field related to (but only minimally overlapping with) one's hobby was not conducive to getting a lot done on the car. Work, as I once heard it said, is like having an early morning class and a late afternoon lab every day for the rest of your life. So the project kind of languished in the end as well. The upside of that job is that I learned a bit about the industry side (as opposed to hobbyist side) of the EV business. After a somewhat miserable year working and living the Los Angeles area, I moved up to Bellingham to do a one-year post-bacc program in Vehicle Design at Western. I not only learned a ton about cars in general, I also became more interested in the dark side (internal combustion vehicles). After playing around with a couple of diesel Rabbits and turbocharged all-wheel-drive Mazdas, I'm pretty well back in the EV camp as far as projects go. There is one other project I've worked on that's worth mentioning, my so-called Three-Wheel Dork Mobile. This stems from an idea a friend and I had back in 1996 of building a motorized skateboard with front and rear weight sensors controlling the motor. After years of thinking about how to put it together and a few false starts, I put one together a year ago that I've been riding around on ever since. Here's a picture of it in it's early stages. Basically I'm interersted in any kind of interesting or unusual drivetrain in a car, and building an EV is an especially accessible way of radically changing what powers a car. And the end result should handle a good half of the driving I do for pennies a day worth of electricity.