AC Fan speed control

[dxpwny]

I've been playing around with various means of controlling fan speed. The fan is a 'typical' 20 inch window fan with 3 speeds.

I have a variac and like the ability of that to control the fan speed.

I've tried a fan speed controller that I'm pretty sure uses a triac. That causes the fan to emit a humming noise.

I know the key difference between a variac and triac is that a variac limits the amplitude of the AC signal, where as a triac limits a portion of each cycle of the AC signal.

With the triac control, is there anything that can be done to reduce the humming ?

I've thought of building a ciruit that detected the zero crossing point in the AC voltage. Then using that to shut off the AC for a variable number of full cycles. Is that type oc circuit reasonable ?

I'm not at all sure of the fan type / motor circuit.

 

[KlausST]

Hi,

It depends.
It depends on the sound ..or better say it's source.

* maybe the sound is caused by the high rise rate of the edges --> then a LPF between triac and fan may do the job.
* or it may be some low frequency jitter in phase angle --> use a better ZCD circuit or timing control circuit
* or it may be from some DC residual in the triac output voltage --> use a better ZCD circuit or timing control circuit.

Klaus

 

[snajperisti]

Are you using a Solid-sta relay with a triac inside or just a single triac?

 

[dxpwny]

I've tried a few controls, like a Leviton 6616-1XW. I don't beleive any of the controls I've used have a solid state relay.

 

[Easy peasy]

a big inductor in series with the fan load may help - if so, a good sized snubber needed across Triac too ..