On 5/5/2010 5:34 AM, Wild_Bill wrote:
Variable speed controllers do exist for single-phase motors, but they
are relatively expensive.
I found several products a number of years ago, just because I was
curious, as several comments here in RCM (back then), stated that
single-phase motors could not be speed controlled/regulated.
I don't recall the products' makers now, but the controllers weren't
intended to be connected to just any common motors, such as split-phase
types, although I'm fairly certain that the specific motors were not the
PSC permanent-split-capacitor types.

However, PSC motors are controllable with variable speed drives that are
made for PSC motors. Oriental Motor (Japan) makes many models of speed
controlled PSC motors and controllers, which are generally under 1/8 HP
(lots of gearmotors where torque is increased by gear reduction).
PSC motors can be controlled to run over a wide speed range.
The AC capacitor used with PSC motors is typically a small value (under
20uF, sometimes single digit), and is wired full-time in series with one
of the motor's two windings.
When the capacitor is rewired differently (permanently or with an
external switch), the motor rotation is reversed.
One of the features of PSC motors is that they can be quickly reversed
by switch motion (unlike split-phase motors which need to be stopped to
reverse them).

Split-phase motors, with their separate start and run windings and
centrifugal switches aren't easily speed controlled, because slowing the
rotor to a point where the centrifugal switch closes again (start
winding energized again) is a bad idea.

Thanks for the info, Bill.

Turns out the garbled text was referring to a *gearbox* without motor
in an eBay listing. Very puzzling.

This has been educational nonetheless.

--Winston