How to control AC fan speed?

[eev_fan]

Motor is 220 volt and have 3 separate windings for low, med and high. I want to be able to lower the speed in the low setting.
Have tried with a cheap wall mounted dimmer, but that did not work properly. Motor is giving off a humming noise and the dimmer have to be set at maximum to start it turning.

Have found this: https://uk.rs-online.com/web/p/fan-speed-controllers/9196248

Will it work?
Any cheaper Chinese alternative? I do not need to adjust the speed once it has been set, but have to be sure the motor starts turning next time I switch the fan on.

[james_s]

Interesting that an American company made 220V 50Hz motors.

That looks like a shaded pole motor, I would expect a triac based motor speed controller like the one you posted would work, they're very similar to the light dimmer you tried but with some modifications that enable them to better handle inductive loads. Here you can find similar controls cheaper made for ceiling fans but I have no idea what's available where you are.

[TimFox]

I worked for an American company before retirement, and we exported equipment to 50 Hz countries.
One of our clients was a large Japanese company:  due to the 50/60 Hz partition of Japan, all their factories had electrical switchboxes for both frequencies.
This presumably gave them a small advantage for exporting.

[Circlotron]

I have an AC exhaust fan that I slowed down using about 10uF in series with the mains supply. Your motor may need 2 or 3 times that capacitance. Use a motor run cap. Not a motor start cap. Advantage of using a capacitor is the full sine wave still gets supplied to the motor so it should be quiet.

[Kim Christensen]

Have tried with a cheap wall mounted dimmer, but that did not work properly. Motor is giving off a humming noise and the dimmer have to be set at maximum to start it turning.

You'll see a lot of multi speed fans set up that way... Speed controller is always in this sequence: OFF, High, Med, Low. Modify your dimmer so it does the same. (Swap outer legs of POT)
That way, when you first turn it on, it always starts.

[sparkydog]

Motor is giving off a humming noise and the dimmer have to be set at maximum to start it turning.

Speed controller is always in this sequence: OFF, High, Med, Low. Modify your dimmer so it does the same. (Swap outer legs of POT)
That way, when you first turn it on, it always starts.

Obligatory explanation video: https://www.youtube.com/watch?v=hQ3GW7lVBWY.

[Seekonk]

I replaced my old gravity feed furnace with a new one. The old ducts were over sized and even the slowest motor speed was too fast with little restriction.  I used an auto transformer to lower the voltage slightly. That increased the motor slip.  Too much and you can burn out the motor. It has been running for over 20 years, must have guessed right.

[Siwastaja]

You'll see a lot of multi speed fans set up that way... Speed controller is always in this sequence: OFF, High, Med, Low. Modify your dimmer so it does the same. (Swap outer legs of POT)
That way, when you first turn it on, it always starts.

Unless the user rotates the pot too quickly past the HIGH setting... These things suck, and the buzzing triac dimmer noise from the motor is very questionable because usually the #1 reason to slow it down in the first place is to reduce audible noise.

[David Hess]

A 240 volt variac or autotransformer will work to adjust the speed.

[eev_fan]

Interesting that an American company made 220V 50Hz motors.

It's an Honeywell F59 electrostatic air cleaner. 8000 volts. Has served me for 40 years...
Only problem is that the low speed makes to much fan noise. I "fixed" it back then by connection a 60W 220V lightbulb in series with the Low-winding.
But todays focus on environment and energy prices made me look for a more efficient solution...

Speed controller is always in this sequence: OFF, High, Med, Low. Modify your dimmer so it does the same. (Swap outer legs of POT)
That way, when you first turn it on, it always starts.

Thanks, but I want to set the speed once and for all, not every time I turn on the unit.
Also, with this dimmer the motor is noisy after being adjusted for low speed.

[eev_fan]

I suspect my dimmer to be PWM.
Would it be a better choice to go for an adjustable switch-mode supply?

[schmitt trigger]

I also second the suggestion of using a capacitor in series with the winding. That is the way my ceiling fans lower their speed.
Again, as others have mentioned, you have to use a capacitor rated for continuous “run” operation. 

How much voltage are you dropping actually with your light bulb? With that value and the current consumption, you can calculate the required capacitor reactance. And knowing the reactance, you can calculate the capacitance at your power line frequency.

[bdunham7]

Thanks, but I want to set the speed once and for all, not every time I turn on the unit.
Also, with this dimmer the motor is noisy after being adjusted for low speed.

As mentioned earlier, a capacitor in series is the way to go.  Use the low-speed winding and add a 5-8µF (my best guess) motor run capacitor in series.  You'll need to experiment to find just the right value.

Phase-control for induction motors is not generally a good idea, although it may be marginally useful for short-duration applications.

[eev_fan]

As mentioned earlier, a capacitor in series is the way to go.  Use the low-speed winding and add a 5-8µF (my best guess) motor run capacitor in series.  You'll need to experiment to find just the right value.

Yes, many thanks. But I haven't any of these capacitors to experiment with. My biggest unpolarized 220V capacitor is .47uF...

[bdunham7]

Yes, many thanks. But I haven't any of these capacitors to experiment with. My biggest unpolarized 220V capacitor is .47uF...

Perhaps buy a few--or a multi-section version--so that you can get a variety of values depending on how you connect them.  Here's an example:

https://www.amazon.com/CEILING-CAPACITOR-CBB61-4-5uf-WIRE/dp/B017G5HKHM

You can get a number of values from about 2 to 15µF with that one unit.

[Kim Christensen]

The light bulb was particularly well suited for this because it's low cold resistance would give the motor a voltage boost when the power comes on.
You might want to experiment with a variac to make sure the motor will start at the required lower voltage without that "kick" to start it turning...
 

[SeanB]

As mentioned earlier, a capacitor in series is the way to go.  Use the low-speed winding and add a 5-8µF (my best guess) motor run capacitor in series.  You'll need to experiment to find just the right value.

Yes, many thanks. But I haven't any of these capacitors to experiment with. My biggest unpolarized 220V capacitor is .47uF...

Go out and find the closest scrapped airconditioner, you will find the fan motor capacitor is between 6 to 10uF, which is a good start.

[wraper]

Interesting that an American company made 220V 50Hz motors.

That looks like a shaded pole motor, I would expect a triac based motor speed controller like the one you posted would work, they're very similar to the light dimmer you tried but with some modifications that enable them to better handle inductive loads. Here you can find similar controls cheaper made for ceiling fans but I have no idea what's available where you are.

US has a split-phase system. So nothing surprising if it goes into high power device powered from double the normal mains voltage, electric stove for example.

[james_s]

I replaced my old gravity feed furnace with a new one. The old ducts were over sized and even the slowest motor speed was too fast with little restriction.  I used an auto transformer to lower the voltage slightly. That increased the motor slip.  Too much and you can burn out the motor. It has been running for over 20 years, must have guessed right.

That's a nice problem to have. Every old furnace I've replaced had ducts that were undersized for modern high efficiency furnaces and it has always been a challenge to get the static pressures as low as would be ideal. I've never encountered a gravity feed furnace, the oldest I've come across were mid 70s forced air models that were only 70% efficient. The lower efficiency forced air furnaces ran a much higher bonnet temperature so much less airflow per BTU was required.

[james_s]

Interesting that an American company made 220V 50Hz motors.

That looks like a shaded pole motor, I would expect a triac based motor speed controller like the one you posted would work, they're very similar to the light dimmer you tried but with some modifications that enable them to better handle inductive loads. Here you can find similar controls cheaper made for ceiling fans but I have no idea what's available where you are.

US has a split-phase system. So nothing surprising if it goes into high power device powered from double the normal mains voltage, electric stove for example.

I'm very familiar with the split phase electrical system we have here. It is 60Hz though not 50, and it's 240V rather than 220. You'd never find a 220V 50Hz rated motor in any American appliance.

[james_s]

Yes, many thanks. But I haven't any of these capacitors to experiment with. My biggest unpolarized 220V capacitor is .47uF...

Buy one. No need to experiment, just calculate the value. Measure the voltage across your 60W lightbulb and the current through it with the motor running and then use Ohms law to calculate the resistance of the bulb under those conditions. Then plug that value into the equation for calculating capacitive reactance and that will give you the value of capacitor you need.

[eev_fan]

Many thanks.
Voltage drop is 90v across the bulb and current 160ma. So it's not a big loss...
Found this page which says:

Initially single phase motor needs little rotor push to rotate the rotor at the rated RPM. Selection of right capacitor for single-phase motor is really tough, it could lead to starting the motor or not.

Maybe the bulb solution is working because an incandescent light bulb, when switched on, only has around 1/15 of its operating resistance. And that's enough to get the fan started?

[Doctorandus_P]

One way of controlling motor speed is with a triac, then turn it on for a half or a full cycle, then turn it off for a few (half) cycles. Some 30 (+) year ago this used to be done with some 555's and but these days it's more logical to use a small uC for this, and you can probably find a few of such projects on those git collection websites.

[james_s]

Maybe the bulb solution is working because an incandescent light bulb, when switched on, only has around 1/15 of its operating resistance. And that's enough to get the fan started?

Well if you have a 560 ohm resistor that will be pretty close and you could try that, it will be dissipating almost 15 watts though. Fan motors require very little starting torque because  fan doesn't draw any load from the motor until it gets spinning.

[tooki]

Interesting that an American company made 220V 50Hz motors.

There’s this thing companies do, called “exporting”, where they sell things to customers in other countries. And to do that, they need to make the things the customers in those other countries want.

Where you live, you can identify things that were exported to USA because the “made in [country]” declaration will name a country other than “USA” or “America”. For example, if you buy a real Swiss Army knife, the box will say “Made in Switzerland” (which is a real place, not a fantasy thing made up for a theme park!). Sometimes, manufacturers will leave off the “made in” part and just write a country name on the thing.