Sparky has asked how low the fans will go on a speed controller - really checking that they can go significantly lower than the slower of the two speed options.
Using the S&P TD250.
This impacts on the box we put in the wall, and we are doing that at the moment :-)
IIRC someone was using a speed controller (previous post).
Cheers
Dave R
Very much suck it and see IMHO. no pun intended. Typical phase angle dimmers are not designed for motor loads but there are some with designed for use with transformers which are also inductive and should give you some control over the fan motor.
I have a big tangential blower in my loft with a permanent split phase
1/2 hp motor the speed of which should solely be dependent on mains frequency but driving it from a variac, the change in voltage does give quite good speed control although I'm careful to never let it stall by dropping the voltage too low. This would be an expensive solution to buy a new variac but if like me you have one from the junk box, it might be worth a try.Bob
The main limit to reducing speed for any motor is that the motor's own cooling fan can't provide adequate cooling and it overheats. Reduced speed and variable speed drives often have to have oversized cooling fans or a separate, fixed speed, cooling fan motor to allow them to operate at low speeds.
SteveW
Yes. Be aware of the issues of slowing a motor down using a chopped waveform: as suh te motors back EMF is low, and theredfore peak currents are much higher, and I squared R can result in MORE dissipation at lower speeds than at full, in motor and controller, before the falling duty cycle lowers overall heating. In these cases you are relying on the motors internal resistance and inductance to limit peak currents and these are highly moveable feasts.
Its a problem so often heard on the model plane RC field 'but I was throttled back!' (when the magic smoke came out).
Just to note that the fan controller is from the same source as the fan (S&P).
One assumes that someone has therefore sized it correctly. Not always a valid assumption these days
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the thyristor control on my weird kitchen extractor (250w shaded pole motor I think, 4" dia by 6" long) slows it OK to around half speed, but once it's stalled it needs near full power to restart.
rusty
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