I cannot believe how difficult it has been to get technical information
for the kind of three speed fan being discussed. I Googled various
terms. Without heavy restrictions, millions of hits were made without
I did find something that showed how to switch from two-pole to
four-pole operation on for a single phase induction motor.
I did find an ambiguous description on how to get three (or) more speeds
from a universal motor by switching what would be the field winding of a
series dc motor. Good fans seem to operate with motors without
commutators. I do not know if universal motors are used with fans. I
would think induction motors would be more reliable and cheaper.
If someone has good links, please pass them along.
I did get to a catalog posting of a motor controller, offered by
Granger. I think it was a variable frequency drive. If so, the output
voltage was not reduced at low frequency.
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