AC Blower Motor Speed Control

[danadak]

Not an expert here on motors.

Have a small blower motor, << 1 HP, with start capacitor, and I need to confirm if there
is a centrifugal switch circuit employed on startup cap.

A phase control approach, using a triac, not workable, right ? Due primarily
to startup speed switch and its lower limit on disconnecting startup cap ?
And the presence of cap in startup not suitable as well with triac approach ?
VFD the only real way to do this ?

What is easiest method to approach speed control in this situation ?


Regards, Dana.

 

[fourtytwo]

I believe it is a synchronous motor so to change speed you need to change frequency.
However a capacitor start motor is a sort of 2 phase motor, I am not sure there are vfd's that are compatible.
Some of these motors retain the capacitor for normal running & the start centrifugal switch changes the winding impedance from very low for starting to higher for running but the capacitor is still in circuit to provide phase shift.
Unfortunately the are all different!

 

[danadak]

I believe it is a synchronous motor so to change speed you need to change frequency.
However a capacitor start motor is a sort of 2 phase motor, I am not sure there are vfd's that are compatible.
Some of these motors retain the capacitor for normal running & the start centrifugal switch changes the winding impedance from very low for starting to higher for running but the capacitor is still in circuit to provide phase shift.
Unfortunately the are all different!

Thank you.

 

[MaxHeadRoom78]

Generaly start switches are used/needed on motors above 1 HP and usually have a start cap, as well as the run cap.
Often these smaller fan motors just have a continuos fed , phase shifted start winding.
But 1ph induction motors do not control well using speed control methods.
This is why those that require AC motor control generall use the 1ph input VFD with 3ph output & 3ph motor.

 

[ahsrabrifat]

Not an expert here on motors.

Have a small blower motor, << 1 HP, with start capacitor, and I need to confirm if there
is a centrifugal switch circuit employed on startup cap.

A phase control approach, using a triac, not workable, right ? Due primarily
to startup speed switch and its lower limit on disconnecting startup cap ?
And the presence of cap in startup not suitable as well with triac approach ?
VFD the only real way to do this ?

What is easiest method to approach speed control in this situation ?


Regards, Dana.

If your blower motor is CSIR with a centrifugal switch, then phase control is not workable, as you guessed.
VFD with 3-phase motor swap is best for full range variable speed. For minimal effort, replace with a PSC blower motor if you're open to a motor swap and just need basic speed control.