AC Fan motor speed control ideas

[kaboom]

Re: AC Fan motor speed control ideas

I don't have one of my exact fan, but when I pulled out its impeller because it seemed a bit wobbly and I tried balancing it a bit better, I had a look behind it and I can confirm it looks just like the one in post #16.

Okay, then remove the two screws holding the bearing retainers and reassemble with the stator flipped.
The leads will exit opposite their usual place, check for mechanical interference.

It's most certainly a shaded pole motor.
When you have it apart, you'll see the heavy copper shunt bars, which is what makes them self-starting without multiple windings & a run cap or centrifugal switch.
Woodgears just shows a larger, C-frame one (that powers a gearbox).

Incidentally, those shading shunts are what limit these motors to some awful efficiency, something on the order of 30 percent.
They then exist, after the motor's at speed, as shorted turns!

[Dannyx]

Re: AC Fan motor speed control ideas

How about a picture of the motor?

I don't have one of my exact fan, but when I pulled out its impeller because it seemed a bit wobbly and I tried balancing it a bit better, I had a look behind it and I can confirm it looks just like the one in post #16.

[redwire]

Re: AC Fan motor speed control ideas

How about a picture of the motor?

[Dannyx]

Re: AC Fan motor speed control ideas

If it's a shaded-pole motor, you can flip the stator or the rotor, to reverse direction: https://woodgears.ca/reader/walters/reverse_motor.html

No, it's most likely similar to the one shown in post #16, hence why I think all I have to do is flip the rotor around. A shaded pole motor would be too big to fit in a fan like this.

[redwire]

Re: AC Fan motor speed control ideas

If it's a shaded-pole motor, you can flip the stator or the rotor, to reverse direction: https://woodgears.ca/reader/walters/reverse_motor.html

[sam_sam_sam]

Re: AC Fan motor speed control ideas

I do not know if this will work or not but give it a try

[Dannyx]

Re: AC Fan motor speed control ideas

Can you reverse the fan blade?

No. Most likely the blade is going to have only one shaft insert on one side, unless I get really lucky and the hole indeed goes from one side to the other, which I've rarely seen.

[TechGeek]

Re: AC Fan motor speed control ideas

Can you reverse the fan blade?

[Dannyx]

Re: AC Fan motor speed control ideas

Speaking of these motors: any way to get them to spin backwards ? I was planning on mounting one on the door of a storage closet to suck the hot air out from the top, but it then became obvious that all these fans suck from the front and blow out the back. You'll immediately suggest mounting the fan on the inside of the door, but the point is the faceplate has to be on the outside of the door so it looks somewhat nicer and I don't just have a hole in the door where you see the back of the fan, so I'd need the blades to turn the other way somehow...I think I can take the rotor out and flip it 180 degrees...

[Dannyx]

Re: AC Fan motor speed control ideas

I don't really need a range of speeds, but rather two settings: full speed and low speed ("quiet"), which I plan to use a time relay to switch between at certain hours when it's "nap time", so once I'm satisfied with the noise level, I would no longer adjust anything anyway, hence why fixed solutions like series resistance are also acceptable. A continuously adjustable circuit just makes it easier to find said sweet spot, as opposed to trying out different solutions which yield a single fixed speed at any given time, plus it's more professional and possibly more efficient.

I came across those SCR devices like in the last picture, but thought they're the same thing as my triac setup and wouldn't perform any better in the long run, so I disregarded them...

[redwire]

Re: AC Fan motor speed control ideas

A surplus dealer had a bunch of cheap German 240V fans, but normal is 120V.
We added a series capacitor to get resonance to 240VAC with 120V supply, it worked well. But trying different cap values it was not going to make a Tesla coil, the Q is low due to the motor's DC resistance and load of the rotor, it is a lossy circuit. I found the motor's inductance alone was enough.
I thought of OP using a small motor cap below resonance as extra impedance to slow the fan down. It won't make buzzing noise.

For better control range, a triac dimmer with the extra (cap reset) diodes works much better. I use the Ali "4,000W SCR" board (hint: it's a triac) with motors and fans and it works IF the pot is the right value for your mains voltage and other resistors are not just copied. This schematic is after I fixed it. No EMI inductor on it. Look for a small bridge rectifier to tell it's the right one.
Your dimmer might just be junky and need resistors or trigger cap size tweaked. App note on dimmers AN1003

P.S> A light bulb would work too.

[Dannyx]

Re: AC Fan motor speed control ideas

Just for reference, here's also the first dimmer I tried - the one with the slider, whose buzz I wasn't too satisfied with. It actually does have the coil you chaps mentioned, so that's probably one positive thing going for it. I haven't analyzed it yet, but I reckon it's the same exact circuit thing as the one on Aliexpress, just with the coil and the little neon lamp, which I'm not sure affects the functionality in any way, other than to offer a visual indication of the setting.

Trouble is, one faint nudge on that slider down and the motor already slows down a lot, so I'd probably have to modify it a bit...

Still, I'd much prefer a transformer since it appears to run more smoothly, but what specs should the transformer have ? Should it be rated close to the same power as the motor ? Does the secondary voltage matter ? Do I just wire the primary in series with the fan ? If so, then with no load on the secondary (open circuit), would the fan run at its full speed ? My fan draws 14w according to its label, by the way.

EDIT: I just got another idea, which I actually tried out, since it's really simple to do: low wattage incandescent bulb in series with the thing. I tried 20w, the smallest one I had around and it slowed down quite a lot, close to how I want it. I'd then use a relay or a switch to bypass the lamp to enable full speed. True, this is highly counterproductive, since I'm now wasting power as heat which the lamp gives off, which is the opposite of the whole purpose of a fan to begin with, but assuming I place the bulb somewhere remote where temperature doesn't matter, it works quite nicely

[kaboom]

Re: AC Fan motor speed control ideas

If you have any motor caps, try a 5uF or something.

Do NOT do this!!!


Depending on the load & leakage inductance and other characteristics of the motor, there's the very real risk of series resonance. It is possible (likely?) to end up with greater-than-normal voltage across the motor, with excess current draw and core saturation, even though the calculations for Xc suggested otherwise.

Do NOT assume the motor's reactance is inert for at least part of the fan speed/torque curve.

In testing, a "C-frame" shaded pole motor (1980s MWO fan) in series with a ~6u cap ended up receiving ~160V while drawing close to an amp, vs its normal .6A @ 120V.


OP, your fan uses a similar "round" shaded pole motor:


Use a triac based motor speed control; looks similar to a light dimmer but has off/hi/lo markings.
The buzz is normal as the fast risetime is audible via the core&coils.

[redwire]

Re: AC Fan motor speed control ideas

With a rheostat or resistor, you are wasting the extra (voltage) energy as heat. Using a transformer the voltage to a load resistor is just lower voltage and isolated from mains.

[Dannyx]

Re: AC Fan motor speed control ideas

Another approach is to put a transformer (primary) in series with the motor, then load down the transformer's secondary with a smaller rheostat or resistor. It's safer and not as much smoke.

Sounds nice and hacky, just the way I like it, though as you suggested in the very last sentence, I think there's a little bit more to it than just randomly picking out a transformer out of my junk bin

[redwire]

Re: AC Fan motor speed control ideas

Another approach is to put a transformer (primary) in series with the motor, then load down the transformer's secondary with a smaller rheostat or resistor. It's safer and not as much smoke.

[Dannyx]

Re: AC Fan motor speed control ideas

Rheostat?

I thought of that too, but have no idea what value it should have and what I should look out for so it wouldn't go up in flames overnight

[TechGeek]

Re: AC Fan motor speed control ideas

Rheostat?

[sam_sam_sam]

Re: AC Fan motor speed control ideas

VFD = correct solution!

Yes but not for 120 volts these are rare

[eccerr0r]

Re: AC Fan motor speed control ideas

VFD = correct solution!