On 7 Oct 2013 at 23:30, Robert Troll wrote:
I would like to power this one with house current.
Ah, then that's another story altogether. Why didn't ye say so before,
laddie? ;-)
You could rectify and filter the AC line, and use it as input to a DC motor
controller which can handle ~120v input. A pwm controller is in effect a
DC
transformer.
Then you need a way to limit the controller's output to 36-40 volts.
If you were a EE you could probably come up with something that would
dynamically monitor output voltage and adjust the control resistance
appropriately. Most (but not al) controllers use increasing resistance on
the control potentiometer to mean "more output."
But for a simple fixed limit, you could just use a lower value pot than the
specified one. A wild guess would be maybe ~1600 ohms (a typical
controller
pot is 5k). You might also parallel a fixed resistor of maybe 2.7k with
the
5k pot. In practice you'd probably have to determine the right value
experimentally, using a light bulb in place of the motor, until you found
the right value.
Now the rub is that while 36 and 48 volt controllers are almost commodity
items because of their ubiquity in the golf car world, 120v controllers are
not as common and thus cost more. A Curtis PMC 1221C-7401 from evparts.com
will run you almost $1400 plus shipping. (By way of comparison, they offer
an Alltrax 24-48v, 300a controller for $327.)
But I wonder if you really need anything that sophisticated.
With a PM motor, RPM is proportional to voltage applied. You have to limit
voltage so you don't over-rev the motor, and limit current so you don't
overheat it.
I'm not an engineer, but I wonder if you might try a simple series
resistance between the motor and the rectified line. You can calcluate the
series resistance needed with Ohm's law, if you know the motor's running
current. You could also determine it experimentally, by starting with a
very high resistance and gradually trying lower ones until the motor
voltage
was about right.
A light bulb makes a nice, cheap power resistor. You could make a crude
speed controller by using several bulbs in series, and having switches or
relays that would bypass the lamps one by one to increase speed.
The downside of a series-resistance controller is that torque and speed
regulation under load aren't good. Under load, the motor wants to draw
more
current. Its effective resistance goes down, so the voltage across it
drops.
But then a lot of ETers are happy with their stock GE controllers - and
that's how THEY work. So ...
David Roden - Akron, Ohio, USA
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to the "etpost" address will not reach me. To send
me a private message, please use the address shown at the bottom
of this page : http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
_______________________________________________
Elec-trak mailing list
Elec-trak cosmos phy tufts edu
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak