On Jul 13, 12:11*pm, bud-- wrote:
Tony wrote:
Lee B wrote:

Current house came with a whole house fan (not an attic fan, but the
kind in a hallway ceiling that sucks air into the attic). I was happy to
see that because I really liked the one in my old house. However the one
in the old house had a variable speed dial on it, and the new house's
fan has just one speed - high and loud with a simple off/on switch.

Is the variable speed a function of the fan itself or can that be added
at the switch? I'd definitely be having an electrician do it, but I'm
just trying to figure out if it's even doable, or if I'd end up needing
an entire new fan. And if so, would replacing an existing fan and switch
be difficult (ie cost me an arm and a leg)?

My fan has a 2 speed motor. The 2 speeds are from separate windings -
each speed has a different number of poles in the motor.

You can easily control a "universal" motor - the type with brushes. Not
likely that is what is in the fan.

Three phase motors can be controlled by changing the frequency. No
possibility there is a 3 phase motor in the fan. The control would be
relatively expensive. I have never seen info, but I suspect the new
variable speed furnace motors are of this basically this type.

You could probably use a variable frequency control for a standard
induction motor, but if the speed falls to where the start switch in the
motor turns on you will probably burn out the motor. And probably
relatively expensive.

If you use a "phase angle" controller, like a light dimmer, you could
control the speed - the motor speed falls farther from the "rotating
field" speed. Has the same problem with start switches. I believe the
torque falls rapidly as the speed drops, but the power required for a
fan, if I remember right, is about the 4th power of the RPM.



What is the voltage and amperage ratings of the motor? *Here are some
speed controllers to choose from.

http://www.amazon.com/s?ie=UTF8&rh=n...20Contro... *

Briefly looking at the info for one of the speed controllers, it says it
is for shaded pole motors (which are used in clocks and my bathroom fan)
* and permanent split capacitor motors, which is not likely what is
being used for the fan. Not obvious from what I saw that the 10A speed
control would work for a typical induction motor, which is probably what
powers the fan. These controls are probably "phase angle" controllers -
as above.

Outside of a 2 (or more speed) induction motor, I don't know how you
reliably control the speed of an induction motor that probably powers
the fan. How does the control work? How do you avoid problems with the
start switch?

--
bud--


Mine works great, the KB controller I got hooks up in series, I capped
the low speed wire on the motor and just use the high speed one.