Ok everyone, I was wondering if anyone had any clue on how to regulate
the speed of a standard induction AC motor via the parallel port on a
PC. Any help would be great. Thanks, Lucas.
Hi, Lucas. There are many types of AC induction motors. For permanent
split-capacitor and shaded pole types, a standard triac phase control
circuit works pretty well (view in fixed font or M$ Notepad):
| _
| / \
| .---------( M )-----o---------------------o--------.
| | \_/ | | |
| | | | |
| | .-. | |
| / \ R1| | | .-.
| (A C) | | | | |100
| \_/ '-' | | |
| 120VAC| | | '-'
| | | | |
| | .-. | |
| | P1| |<---. | |
| | | | | Q4010 | | .1uF
| | '-' | _|_ --- 400V
| | | | |<| V_A ---
| | o-----o----|\|------/ | |
| | C | |>| | |
| | --- DIAC | |
| | --- | |
| | | | |
| | | | |
| '-------------------o---------------------o--------'
|
(created by AACircuit v1.28.6 beta 04/19/05
www.tech-chat.de)
This doesn't work all that well for capacitor-start induction motors.
It works best with fans and blowers, which require very low starting
torque and where small changes in applied voltages can produce big
changes in blower output. You'll generally have more of a tough time
with low speed control on this.
Values for C, R1 and P1 are left as an excercise for the intrepid
student (and also are dependent on the diac chosen).
If you want to do this with a printer port, you're going to have a
tough time replacing the triac trigger with a digital output, mostly
because of latency issues. There's just too much to do in a modern PC
to pay attention to when the zero crossing of the AC line occurs.
As a practical matter, it might be easier to buy/build a controller
which will accept an isolated DC voltage input, and do the controlling
of the triac based on that voltage. You can then just output an analog
voltage to the controller with an ADC (which is trivially easy to do
with a printer port if you can live with 8-bit resolution or less).
You can then purchase an AC triac motor control with isolated analog
input control voltage. If this is a class project, you might want to
think of improving on the Velleman K8064 DC-controlled dimmer
http://www.vellemanusa.com/us/enu/product/view/?id=521945
It requires 0-12VDC control, and apparently doesn't turn on until V(in)
is greater than a couple of volts. But it's a start -- the
optoisoolation is critical here, unless you want to turn the laptop
into a pyrotechnic display or get somebody hurt. Also remember that
this kit isn't made to drive inductive loads -- I'm not recommending
you buy the kit, just look at it as a starting point.
I hope this is of help. If you'd like more information, feel free to
say a little more about what you're doing.
Go Illini!
Chris
