Re: AC to DC drive

[XURQ03A@prodigy.com ( LEE A HART)]

Mason Convey asked about a 1-speed DC drive in an S10 pickup: A 1-speed DC
drive is possible, but challenging. You wouldn't build it like the typical EV
conversion that has a transmission.

1. Starting torque. A DC series motor can supply the tremendous starting
   torque needed to start out in 3rd gear. But to do so, it draws a tremendous
   amount of current; 600-1000 amps depending on the kind of accelleration you
   want. That requires a *big* motor. A Kostov would be the smallest motor I'd
   consider.

2. Controller. This means a 600-1000 amp controller is needed. There aren't
   many candidates in this range, and none of them cheap. You might be able
   to use two controllers, each feeding 1/2 the motor. This has been done
   successfully but I don't have any experience with it.

3. Cooling. Since the motor is running at high currents and low rpm at low
   speeds, the internal cooling fan is worthless. You would remove it, and
   use an external blower for cooling.

4. Differential. The rear axle ratio needs to put the motor near max rpm at
   the maximum speed you expect to drive. The stock gears are probably 2.x:1
   or 3.x:1. This probably means changing to a lower ratio (4.11:1 etc.).

5. Battery voltage. Motor torque falls as rpm rises. Thus HP falls. So you
   need a high battery voltage to cause a high enough current to flow at max
   rpm so you have enough HP for high speed cruising.

6. Alternatives. A controller is in effect an electronic transmission. At low
   speeds, it multiplies battery current to produce more torque. The wider the
   range needed, the more expensive the controller. There are other ways to do
   the same thing (without a transmission).

   a. Use two motors. Wire them in series for low speed, and parallel for high
      speed. Now the controller only has to deliver 1/2 the current to produce
      the necessary torque. Each motor can be much smaller, which means they
      can tolerate higher rpm, which allows a lower differential ratio without
      losing top speed.

  b. Use a locking torque converter between motor and drive shaft. In some
     discussions with Leon Levasseur, it appears that one could use a torque
     converter (without the automatic transmission) to multiply motor torque
     at low speeds without sacrificing anything at high speed once the
     converter locks up.

Lee Hart                     If you would not be forgotten
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Robbinsdale, MN 55422 USA    Either write things worth the reading
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e-mail XURQ03A@prodigy.com   (Ben Franklin, Poor Richard's Almanac)