Mr. Sharkey via EV wrote:
It's going to be very interesting to hear your report about this van
when you get it running. I can't imagine how they made it even close to
streetable with no gear changes and reverse being changing the rotation
of that motor! You can get away with that kind of stuff with a series
motor.
It works for shunt and sepex motors as well... but only if you get the
details right. Given that this was professionally done, they probably
got it right (or at least mostly right).
As an example, the Chrysler TEVan (EV conversions done by Chrysler on
their minivans) had a GE sepex motor and controller, and no transmission.
A little background on DC motors mught help. A DC motor has an armature,
and a field. The torque is proportional to armature current x field
strength. The speed is proportional to armature voltage x field strength.
An on-road EV needs a *wide* range of torques and speeds. ICEs get this
with a transmission. EVs can too; this lets you "get away" with an
electric motor that isn't quite "up" to the job. But it's a better
design to eliminate the transmission and choose a motor (and controller)
that give you the required torque and speed range.
A PM (permanent magnet) field just has one strength. So you get a simple
relationship; torque = current, and speed = voltage. PM motors aren't
much good for on-road EVs because this limits their torque and speed range.
Forklifts typically use a series DC motor. It has a low-voltage
high-current field winding (like 1 volt at 100 amps), which is simply
wired in series with the armature. This configuration provides very high
starting torque (but very slow), and very high speed (but at very low
torque). It has the advantage of a very simple controller. It has the
drawback of poor regen, and weak performance at high speeds.
A shunt motor has a high-voltage low-current field winding (like 100v at
1a). The field strength is limited by how high a voltage you have
available. They are great for high speeds; but low-speed torque is poor
because you can't get a strong field (unless you can power the field
with 500v!). Again, the controller can be pretty simple. Shunt motors
are great for regen; in fact most generators are shunt.
Now comes the interesting one; the sepex (Seperately Excited). It has a
medium-voltage medium-current field (like 30v at 30a). It requires a
more complex controller with *two* outputs; one for the armature, and
one for the field.
A sepex motor can deliver high torque at low speeds (by powering the 30v
field at say 150v). It can also deliver high torque at high speeds (with
high armature current, and low field current). It's also good at regen.
If it's done right, you get the best of both worlds. :-)
You probably have a sepex motor in this TVA VW bus. That's promising!
But, you'll have to either get the old controller working, or figure out
some way to replace it with something modern. That's going to be hard,
because sepex controllers are normally custom-programmed to match the motor.
After sitting for six years, my motor set up a howl like a cat tangled
in a fan belt when I first got it running again.
I used a surplus aircraft starter-generator in my first EV. This is sort
of a hybrid; it had *both* a series field and a shunt field. In the
aircraft, it used the series winding for the starter, and the shunt
winding for the generator. I used both at once in my EV. :-) The
controller was crude (basically, manual control), but it worked. :-)
Because the motor was already old and grotty when I got it, it too
howled like a banshee. It got a little better from running it; but what
really helped was to have the armature turned in a lathe to true it up
and remove the ages of surface corrosion. Then, I got a "commutator
stone", which is a soft abrasive that you rub on the commutator while it
is spinning to "seat" the brushes so they conform closely.
In any case, good luck! You're in for an adventure in archeological
engineering. :-)
--
If you're not stubborn, you'll give up too soon. If you're not flexible,
you'll pound your head against the wall and miss a different solution.
(Jeff Bezos)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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