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Re: (ET) E20 motor at 48V
Motor Theory
- Basically, these are compound motors meaning there is a shunt field
and additional turns of heavy wire (compound winding) that carry
armature current wound on top of the low amperage separately excited
shunt field. This "main field" produces flux that moves perpendicular
to the armature conductors.
A DC armature actually "generates" voltage called counter EMF that is
just slightly below input armature voltage. It generates it by the
armature conductors moving thru the main field (CEMF = field flux x
conductor length x velocity).
When you apply armature voltage, the armature "draws" current until
voltage produced inside the armature is equal to it (plus the carbon
brush drop - 2 volts) Armature Volts = CEMF + IR + 2v
brushdrop........ (IR is the armature current x resistance)
Torque is proportional to armature amps and field current.
Torque is also proportional to armature diameter squared times length
(D^2 L).
High speed motors are stacked out for low inertia and high speed.
The Disney Cruise Ships are powered by 2-60,000HP ac motors that are 20'
high but only 3' long.....low speed, high torque for propeller shafts.
When a load is applied to the shaft, the motor slows down and the
armature draws current to keep voltages equal. If you decrease armature
volts when it's running, the CEMF is higher than applied volts and the
motor generates (moving amps the other way to lower speed).
- When you run current thru a wire, it produces flux which encircles
it. At higher loads the armature conductors produce enough flux or
armature reaction, that it decreases the shunt field flux which makes
the motor run faster. Those additional turns of heavy wire carrying
armature current wrapped around the shunt field "add" flux to offset the
armature reaction and make (or tune) the motor speed at higher load.
- When the motor is reversed, the compound (or stabilizing field) is
not reversed as it would require another large contactor. This field
then "weakens" the shunt field flux causing the motor to run faster in
reverse.
- These motors are termed electric vehicle motors and typically rated
for 200% amps.
36V 3600RPM 30A .....but can be run at 60 or more for short
bursts providing you don't exceed the RMS rating of 30 amps over time
and the duty cycle is 60 minutes meaning the motor must be allowed to
cool down to almost ambient temperature before running again. This is a
typical rating of crane motors too.....short duty, off and on.
Probably really confused a simple question......
...Walt
-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of SteveS
Sent: Wednesday, January 02, 2008 7:31 PM
To: et
Subject: Re: (ET) E20 motor at 48V
I would think the Honda should be a good chassis for a conversion.
OK, I need some education - can you use a sep-ex controller with these
motors? I thought these motors were, strictly speaking, compound motors,
though I understand they are 'mostly' series motors, with a 'bit' of
shunt field. This is why they run faster in reverse (when the fields act
together). Do I have this right? And if so, can you use a sep-ex
controller with them?
Would the Alltrax be the best controller (even if used in a non-ET
application)?
(I know just enough to be dangerous.)
- SteveS
Jeff Tickner wrote:
>
> I have a spare E20 motor and an old Honda 750 I would love to do that
> with also. I saved the guts of my E15 when I put the Alltrax in for
> the intent of creating some kind of controller, have the throttle
> cable move the lever on the speed control.
>
> I was also thinking of these guys here, a relatively cheap sep ex
> controller, scroll down to the KD36303, 300A with regen for $249
> http://www.kellycontroller.com/mot/Brushed-Motor-Speed_Controller.html
>
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