# Digitally dimming an AC single phase motor

Hello,

I would like to dim a single phase 220V AC motor, digitally, with my arduino of course.

I've read a lot of topics here and on other sites, yet I can't find a satisfying answer. Like, someone say "do this and it will work", then someone else say "no it won't work, do that instead". And then they go about technical stuff that I can't understand because I'm not an electrical engineer... I can't afford to try all offered solutions without knowing what I'm doing, most likely I will burn my motor, or worst..

Can someone please look at the datasheet of my motor (BL-B190A-2E-А01-01), and tell me what would I need to be able to digitally control the speed of it (all I really need is 4 steps: OFF, 1/3, 2/3, FULL). Is there suitable modules available somewhere, like ebay?

Thanks!

That is a synchronous AC motor and to control the speed, you need a VFD (variable frequency drive). They are unfortunately expensive.

• How can you tell it's a synchronous motor?

• Ok so now I know that for digital speed control, I need a VFD. What about manual speed control? Do I need a VFD too?

• According to wikipedia, the speed of a synchronous motor can be calculated by: 120 * ( freq / # of poles per phases ), in the case of my motor it's 120 * ( 60 / (2/1) ) = 3600 RPM. Why does the datasheet of my motor says 2700 RPM? There do not seem to be a gearbox. What am I missing? Is there a speed limiter inside the motor? And if that's the case, couldn't I hack it somehow to reduce speed as I want?

Sorry if my questions sounds stupid...

Thanks!

Looking more closely, that is probably an induction motor, which will rotate more slowly than the magnetic field.

If so, you can control the speed over a very limited range, see: Speed Control Methods of Various Types of Speed Control Motors

According to the schematic on page 6 of the motor datasheet, ( I think ) the capacitor is a run capacitor, as described on this wikipedia page. At the top of this page it is said: "A motor capacitor [...] is an electrical capacitor that alters the current to one or more windings of a single phase AC induction motor to create a rotating magnetic field".

Induction motors cannot be synchronous motors, right? So that would mean my motor isn't a synchronous motor...

Also I know from the datasheet that my motor has 2 poles (the "2" in the motor designation key is the number of poles).

Thank you for confirming that it isn't a synchronous motor.. I hope I am right about the capacitor?

Yes I've read that web page already, amongst a dozen similar. I'm slowly starting to begin to understand something about motors..

The bottom line is that you cannot control that motor in the way you wish (OFF, 1/3, 2/3, FULL) without a VFD, and even with one you may not be able to achieve 1/3 speed. Fan motor cooling by air flow is a consideration.

guix:
According to the schematic on page 6 of the motor datasheet, ( I think ) the capacitor is a run capacitor, as described on this wikipedia page. At the top of this page it is said: "A motor capacitor [...] is an electrical capacitor that alters the current to one or more windings of a single phase AC induction motor to create a rotating magnetic field".

Induction motors cannot be synchronous motors, right? So that would mean my motor isn't a synchronous motor...

Also I know from the datasheet that my motor has 2 poles (the "2" in the motor designation key is the number of poles).

Yes its an induction motor with a run capacitor. It is not "dimmable", don't even try.

MarkT:
Yes its an induction motor with a run capacitor. It is not "dimmable", don't even try.

I have a very similar AC fan with the same way of working.
I got regulate it with a analog dimmer (http://www.ebay.es/itm/2000W-AC-220V-SCR-Voltage-Regulator-Speed-Controller-Dimmer-Thermostat-F5-/291581768387?hash=item43e3a0b2c3:g:mc4AAOSw0HVWEntW) but when I try with arduino circuit I just can't do it (it don't move).

It is possible that as you say it don't work due the "rum capacitor", but only in the digital way?

Anyway, that same AC fan was being regulated by a simply PCB (I got it from a domestic machine and now I want to regulated it for myself) that seems a phase angle control circuit (it hav triacs, MOCs 3023/3063...).
What do you thinks?

Joseiter, are you sure this is an AC induction motor? Try to give it a whirl in the one or other direction. If you're not using the starter winding with the cap, most of the time nothing will start to move. Except if the engine has some asymmetrical pole piece, which is obviously not the case if they used an extra capacitor and starter winding.

But, it looks more like you have a DC motor that is PWM controlled by this simple triac circuit.

Again, single or 3-phase synchonous AC motors need a frequency control, not voltage control.

Read the (entire) datasheet, its a split-phase induction motor.

It's an induction motor and not designed for operation at other than rated voltage. You may or may not get away with slowing it down by reducing voltage FOR A FAN LOAD as the fan torque drops off very rapidly with speed-- and even if it doesn't burn up the speed regulation will be very poor and it will stall at the least excuse.
And don't forget that as the voltage goes down the motor current and thus heating goes up and the cooling from the air goes down.
Many years ago I got involved with this approach to speed control of fans and pumps with a tach feedback and speed regulator. I f you had everything going for you they "worked" but got hot as a firecracker and seemed to me to be more trouble than they were worth.
My advice is "don't do it".

You may or may not get away with slowing it down by reducing voltage FOR A FAN LOAD as the fan torque drops off very rapidly with speed

Or you may start a fire due to over-current when its in the stall region. Not recommended, this is not
the motor for electronic speed control.