Permanent Split Capacitor (PSC) Motor Modified for Speed Control?

Discussion in 'The Projects Forum' started by Dabu13, Jul 19, 2010.

  1. Dabu13

    Thread Starter New Member

    Jul 19, 2010
    I am trying to mod. a permanent split-capacitor motor so I can have variable speed control. my friend suggested that I could probably try using a junction box and PWM light-dimmer switch, but I don't really know how the motor would like that. This is a 3.5 Amp rated motor used in a squirrel cage type blower. I know that there are specialized Variable Frequency Drives used in HVAC, but don't want to spend that kind of money. Does anyone know of a way I can add a cheap (less than $30 USD) control system? If i could get two or even three speed settings I would be golden.
  2. Patman

    New Member

    Sep 16, 2010
    I'd love to find a solution to this problem, I'm restoring a 20-year old Bodine Electric PSC motor for use on a vibraphone, to which I don't have the controller circuit. I need to rebuild it, speed control and all. Huh boy...

    Please help us, anybody?
  3. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
    With a PSC blower you can just drop the voltage, autotransformers and variacs are comonplace in older HVAC installations. You can still get the 3 speed autotransformer type new.

    Given that your current is so low a speed control board , 0-10V input typically, would not cost too much and would be doing the same jod as a high current dimmer board, which would probably be even cheaper.
    (I think velleman do a kit, but you'd have to check the specs.)
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    Whatever you use, if it's a light dimmer type circuit be sure it's rated for inductive loads such as fan motors.
  5. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
    Good point ..... Sorry, I should have specified what specs.
  6. crosswick

    New Member

    Apr 14, 2017
    Hey, me too! I'm currently looking at this:

    Which seems elegant. As far as I can tell at the moment, the speed control circuit in the Deagan Commander II I have here consisted merely of power starving the motor with the 7.5kOhm 5W potentiometer in series with one of the AC leads to the motor, and having the vibrato axes inertia pull the motor RPM down. Not super elegant :D

    The elegant modern solution seems to be to create new sinewaves for the motor at lower frequencies, merely powered by the original AC power sinewave. I have yet to find an off-the-shelf kit for this; perhaps this isn't available because since the time of these relatively vintage PSC motors, other motortypes have been typically used for speed controlled applications.

    Ah here they are:

    But so they're expensive and bulky?

    I guess... they seem to start at 215 euros:

    I wonder whether there's a good and perhaps already popular Arduino-type project for this.

    Nope, DIY VFD is frowned upon, there's too many things to get right: - a figure named there is $125 for an off-the-shelf unit

    Alright, how a about a Chinese unit... 118 euros for

    And 2nd hand on eBay? perhaps something smaller also - ah what have we here, an Arduino expansion board that may be powerful enough:

    Ah no, those Arduino shields are only usable for DC motors.

    Here's one that might be powerful enough, rated for 100W:

    And perhaps those are still sold new somewhere. The motor I want to drive btw (which I already have here new): Shaft AC Gearmotor&Model=N1753&Sort=11737

    I suspect 100W will be enough for this, which makes the earlier 118 euro Chinese VFD frequency inverter a bit overkill at 1.5kW.

    This seems where I'm heading now, provided the choice for this particular motor will be maintained. I haven't researched yet, but I think it will be doable to interface the existing vintage speed dial to this VFD inverter: