Series DC motors are about as cheap as you can get in terms of raw torque and HP per dollar. That's why they're used in forklifts (and electric drills and vacuum cleaners).
I'm not a motor expert, but I suspect that the total system cost is low because the controller is relatively simple. You only need one blinking big switch (semiconductor array) because (1) the motor itself takes care of commutation (turning DC to AC) and (2) the field isn't separately excited so doesn't depend on the controller. AFAIK most (all?) of the drag racers use series motors. You can find out more about that over at NEDRA (nedra.com). So if they have so much torque and power for the money, why doesn't Tesla use series motors? Some possible answers: Their torque characteristics (peak at stall, falling off at higher rpm) are the reverse of an ICE's. That would be unfamiliar and maybe uncomfortable for some ICEV drivers. If you have a manual trans in your series-motor conversion EV, you UPSHIFT when you need to accelerate hard. Because of the mechanical commutator, series motors are noisier and need more maintenance than brushless motors. OTOH, you can't fireball the commutator of an AC induction motor because it doesn't have one. Series motor redline RPM is much lower than induction, for the same reason. Commutators have a tendency to fly apart if they overspeed. A series motor will overspeed if it's run at full voltage with no load. It can easily go from nominal rpm to explosion rpm in a second or less. You need safeguards to detect this and shut down the motor in case something in the driveline breaks. A blast shield on the motor isn't a bad idea. You also need safeguards to detect controller failure, because the typical failure mode for a series motor controller is FULL ON. This is known in Audi-ese and Toyota-ese as "unintended acceleration," and with 750hp behind it, is apt to be fatal. Normally if an induction motor's inverter fails, the car will stop (in some failures, possibly rather abruptly, which has its own hazards). Regenerative braking is a major challenge with a series motor. This is not the same as the plug braking available on some Curtis controllers, which is generally not recommended for use in a road EV. A lot of good and expensive silicon has become smoke trying to handle regen. Very few commercial EV controllers today try to do it. Zapi is the only brand I know of, but there may be others. I'm probably an outlier on this list, since a lot of the DIY folks here are series motor users and like them. However, I might be more similar to your target customer. While I'm not in the market for a $150k high performance sports car, if I were, I wouldn't buy one with a DC series motor. No offense to anyone, but at that price point I expect refinement, and that's just not what you get with a series motor drive. They tend to be more-brawn-than-brain, hair-all-over beasts. But if you like driving an ICE with a wild cam and a loping idle, maybe a series motor would be right up your alley. Another option that's seldom mentioned is a DC sep-ex motor. With a proper controller, its torque characteristic is more familiar and (IMO) better suited to a car. Regen is easy and common. The controller is somewhat more expensive than a series motor controller, since it has to supply field current. However, it's quite a bit cheaper (or should be) than an induction motor inverter, since it doesn't need 3 or more big semiconductor switches. Controller failure still can mean full on and flat out, so your controller logic has to detect that and take action, but the motor won't normally overspeed if suddenly unloaded. The downside is that you still have mechanical commutation, which brings in the maintenance and noise issues. I personally don't know who currently makes a high power sep-ex EV motor. Maybe someone else here does. Hope this helps. David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
