Strange effect with fan speed control

 

Hi

We have a kitchen extractor fan which had the speed control burn out- it
was a pretty crude affair using a huge resistor around 200 Ohm with
sections shunted out with a switch, and this in series with the motor. I
threw it out and bought a solid state speed control unit, the kind with
an external potentiometer to control the motor speed. It works great at
low inputs, however if you try to wind the speed up, the motor starts
"chugging", that is, it speeds up for about 2 seconds, then the speed
dies and drops back, repeating over and over. I guess it must be back
emf from the motor that is causing the current to drop, but it's just a
guess. I have no information about the motor, I guess it's a brushless
induction motor. The speed control is some kind of sealed unit with a
thyristor circuit.

  Any idea how I can stop the motor surge and get more output? It seems
odd to me, even if it is back emf, that the speed never stabilises.

T.

 

The damn thing is broke!  Take it back and get a replacement fan from a
different manufacturer.

Steve

Tom Peel wrote:

 

Is it possible that it was mis-packaged and that you received a "dimmer
switch" instead of a motor control switch?

My variable motor control switch starts at HIGH speed when you click it
on and then reduces as you turn it further clockwise.

This is just the opposite of my dimmer switches which start out low and
INCREASE as you turn them.

Just a thought.
Phil

 

Steve Oakes wrote:

It is not broken.

 

If it wasn't broken, you wouldn't be asking about it making the
"chugging" sound when you wind up the speed.  It isn't normal operation
for fans to make "chugging" sounds.  Take it back or call customer
support so they can tell you it's broken.

Steve

Tom Peel wrote: