AC Crossflow/Barrel Fan Speed Control

[Western]

Hi, I'm after some help please on a fan control setup for a 240V AC fan motor.

I'm building a project that requires a reasonable size fan so went to a friends scrap yard and found a nice looking fan and motor from the indoors portion of a split system aircon. It's a crossflow or barrel fan about 850mm wide including motor and only 19 watts on full.

It's a Galanz GAL4P19A-KND and has 3 ac leads with a 1.5uF cap across one pair ... and a set of 3 wires from a Tach Pulse ... one gnd, one 5V and the tach pulse output.

The problem is that in my naivety, I just expected I'd be able to fudge around and get it to run .... and even if I could only get two or three speeds, I would be happy ... but I'm slowly realising that it's not as simple as that.


I was quite surprised that I was able to power up the board and after pressing a couple buttons on the side ... the fan would fire up and run at a slowish speed ... so I was able to determine waveform parameters for both the drive and tach pulse. Then by bypassing the micro, I tried running it with my pulse generator. It did run it ... but it was like an auto motor with the timing jumping all over the place. That's when I finally realised what the tach pulse is for ... and without it I can't control the motor.

Amazingly, I have found a cct online, but I'm still stuck unless I can work out some sort of control system for this thing.

Maybe I just need to chuck this one and go look for another, though I had done a fair bit of planning around it already. I'll upload some images shortly. Thanks.

 

[Western]

 

[fourtytwo]

The reason the timing is jumping around and the motor sounds rough is your "timing generator" is not synchronized with the mains supply (note the sync signal on pin19 of the micro).
For a simple open loop speed control you could use almost any AC triac control circuit BUT some are DC intended for universal motors.
For a closed loop solution using the Tacho signal a more sophisticated controller is required.
I imagine the original controller controls fan speed based on other sensors such as temperature etc, you might be able to get it to do what you want by spoofing those.

 

[Western]

Thanks for your help. I hadn't noticed the 'Sync' input on the micro, but what you described makes sense.

I think I'll try a basic ac motor speed controller and see what happens ... I know I've got one out in the workshop somewhere. I have been looking for a generic design that includes a tach signal so I can build it myself, but if the simple one works, that'll be good enough for me. Thanks again.