--- In mach1mach2cnc@..., "jagco1998" <jagco1998@y...>
wrote:
I have in my possesion a KB electronic model KBMM-225D controller,
and the opportunity to get a treadmill PM motor(90-130Vdc@1...
full load amperage??)its pretty close to be rated within the
controllers limits(16 A average @90Vdc).
The guy that has it tells me that it more than likely wont work
with
an SCR type controller.I dont see the distinction ...I thought a
PM
motor was a PM motor, and as long as the motor matches the
Voltage/amperage of the controller, that the 2 were compatible.
I was wondering if anyone could tell me if the motor will work with
the controller before I purchase it.... and please explain to me
why
it wont(if thats the case) so Ill have a better understanding of it
all and can match a motor to the controller .
It's not so much that it won't work, it's more that it may not work
well for a motor speed control of any precision. An SCR control acts
as a half wave rectifier (pulsating DC = high ripple). It's
basically a large diode (rectifier) that can be turn on during the AC
cycle. When you turn it on in a given cycle determines the amount of
output. Once turned on, it remains on until the AC waveform passes
through a zero crossing. That works okay with motors that run on
either AC or DC (universal motors like a router). SCR control is
also not very good on the low end of the speed curve unless it has
feedback from the motor, like back EMF voltage, to tell it that the
motor is slowing down. A PM motor will have different feedback
characteristics for the speed control.
The best control for a DC PM Motor is a variable DC supply and some
form of tach or encoder feedback to maintain a constant speed under
varying loads. The next next best thing is a PWM speed control.
There are lots of low cost DC motor speed controls. There are some
differences in PM motors that are rated for PWM service but you are
correct in that most PM DC motors are basically the same. An SCR
controller is not a good DC voltage source.
