"Winston" wrote in message
...
On 5/2/2010 3:42 AM, Ed Huntress wrote:
wrote in message
...
On 5/1/2010 9:32 PM, Don Foreman wrote:

(...)

A capacitor-run induction motor is actually a two-phase motor that
produces a rotating magnetic vector.

http://www.electrical-contractor.net...y/msp2v_01.gif

So, if the claims that were *actually* made in the original
source document were (for all intents) the same as the claims
that I dreamt up, then it is highly likely to be fraud because
the magnetic displacement of the second phase will not occur
at the proper time to support armature rotation, given a
significantly different operating frequency?

--Winston--- Or...... not

Keep in mind that I didn't even try to read the original, but Don's
description of a capacitor-run motor, while accurate, doesn't explain the
whole situation.

Once a motor is running, it doesn't need the second phase.

From the schematic then, the 'start' capacitor causes the current
through the secondary stator winding to be 90 degrees phase - displaced
in relation to the current through the primary stator only during
startup? Huh!

No, that's a capacitor-start motor. A capacitor-run motor has the capacitor
in the circuit all of the time. But the actual phase in the secondary
winding of a capacitor-run motor depends upon rpm (start, accelerate, or
running at full speed) and, to a lesser degree, upon the load on the motor
and thus the phase slippage. Unlike a good three-phase motor running on
proper three-phase current, the phases aren't displaced perfectly in a
single-phase, capacitor-run motor (which behaves like a two-phase motor,
more or less, because of the run capacitor).

There also is such a thing as a capacitor-start, capacitor-run motor, which
has two capacitors, each operating in a different circuit. I've never seen
one that I know of. Don't ask. g


Furthermore, the
second phase only needs to be strong enough, and close enough to proper
phase, to keep the motor moving until it picks up a driving pulse from
the
primary phase. The capacitor typically doesn't produce a perfect
"in-between" phase anyway, even at the designed frequency.

In other words, in a typical application, a capacitor-run motor will
start
through a range of different frequencies (unless the starting load is
excessive) and it will run on them, as well.

That doesn't necessarily mean that it will run well, nor that it will
produce normal starting torque.

We're used to that sort of compromise when using a phase converter
for example.

Interesting stuff. Thanks!

--Winston

Any basic text on induction motors explains it better than I do here. It's
worth looking it up. The Web probably has plenty of resources.

--
Ed Huntress