On Jun 21, 8:38*am, jamesgangnc wrote:
On Jun 21, 8:21*am, Martin Levac wrote:



On 6/21/2011 7:52 AM, jamesgangnc wrote:

The problem is that you can't simply continue to lower the frequency
as the lower the frequency the less effective the induction is. *Also
you will find that variable frequency controllers are pricey.

Your best bet is to find a motor with brushes that you can vary the
speed of with common speed controllers.

I did find that. Cheapest VFD at a glance was $325. Although I don't see
why they should be. Maybe these things are too specialized to be made
cheaply.

It's a fan and there's little I can do about its design. It must be
quiet and that is partly why I want full control over the speed.

That's part of it. *There is not a high demand. *Theoretetically an
inverter design could be adapted to a variable frequency output. *But
you still have to convert to dc, then convert back to ac with a
variable frequency switching supply of some sort. *And you are still
limited by the ability of the induction motor to operate at lower
frequencies. *Even 30hz, which is just half, is far worse at
induction.

Practically all small fans will be built with an induction motor and
speed control will be done via multiple sets of windings. *Brushed
motors are more costly and have issues with brush wear and electrical
noise. *They are seldom found in home appliances. *I have seen them in
blenders though. *Probably because blenders have a lot of speeds.

Your most effective solution, barring finding a fan with a non
induction motor, would be to replace the motor. *That will probably
involve some minor fabrication unless you are really lucky. *Another
option would be a DC motor and a variable output dc power supply.

But as you have found, there is no simple plug in solution for your
problem.

Perhaps a smaller fan. *Or put the fan in a window further away from
you. *If you leave the nearby window open you will still be in the
cross breeze.

+1 to this...

A DC motor in a fan will be easier to control in the manner you
desire and wish to control your fan in for whatever unknown and
insane reasons.you have yet to disclose...

~~ Evan