How do I make this AC fan run?

[redwire]

Re: How do I make this AC fan run?

You just want to lower the voltage for the main winding, but not so much the start-winding takes over, doing all the work.
A series capacitor (with the main winding) can give lower voltage to the motor. But it's a big ugly cap found in larger induction motors start caps, which I am saying use one here as a series cap (not for starting).
You don't want the start-winding doing all the work. I didn't mean change the start cap from the factory 4uF, although that value is "tuned" to the motor's operating speed and at lower speeds the larger phase shift I think needs a bit bigger cap? For best efficiency.

An old transformer connected as an autotransformer would also work. Say giving 195VAC (using a 220V-25VAC sec. xfmr). This is what I use (or old UPS autotransformers) , or a variac. A 10% drop in voltage gives much more drop in speed.

I hope this gives you some ideas but I am not an expert. It's great you are keeping an eye on PF and current draw, as you can slow the motor down but make a ton of heat if it's done poorly.

[Behemot]

Re: How do I make this AC fan run?

The problem is that capacitor in series seems to have to counter the phase shift of start capacitor and than move it further so it needs to be really huge. I think it is really wrong way to have the two battle themselves. And for me it means looking for huge capacitors. I may have some at home from old CCLF light, there may also be the transformer part. But than, you are right, maybe adding induction is more the way to go. I got passive PFC transformer here so if I just strip the cap from it and connect it, it may somewhat help.

[eccerr0r]

Re: How do I make this AC fan run?

Some of these induction motors you really can't slow down...well you can but you have to change the line frequency and I think that sort of is out of the question. Induction motors are more related to stepper motors than regular motors, if that makes it clear why it's frequency dependent.

[Behemot]

Re: How do I make this AC fan run?

Don't think it is so complicated. Every AC drives the speed from 0 to max so possibiltiy of driving it guaranteed, now the question is how…

[tom66]

Re: How do I make this AC fan run?

Well, the motor has to reach speed -- and you'll probably be able to get it to slow down at really low voltages, but it won't have any significant torque.

[Behemot]

Re: How do I make this AC fan run?

The problem is with getting voltage down, resistor is easy and will not interfere with the startup capacitor phase shift, but will also burn insane amount of power.

[tom66]

Re: How do I make this AC fan run?

Variac or VFD is probably the only way. You can get some low power VFDs for cheap, or if you don't need much power (10~15W max) you can build one using a timer circuit, MOSFETs and a mains transformer.

[Behemot]

Re: How do I make this AC fan run?

What about diac-triac regulator? It has some strange V-A characteristic but I think it would not interfere with phase shift, at least not much.

ADD// Seems that asynchronnous motors do not like triac reguation much. So only option for me is to lower amplitude or change frequency. So transformer with 150-170 V output?

ADD2// I got some old transformer with no use here, 3x5x6 cm iron core. Do you think it's worth trying to change the windings to 23:16 ratio?