On Sun, 2 May 2010 18:24:46 -0400, "Ed Huntress"
wrote:


"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).

But they might be if the second phase is electronically synthesized
rather than being produced by a 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

The diagram at the link Winston posted is exactly that. Some consumer
air compressors use this approach. They're easy to spot, there are two
caps on the motor. They're sort of sneaky ******* motors. They are
basically cap-start motors but they feed a little cap-run thru the
start winding to get a bit more power with same temp rise and same
line current with better power factor.