Eric R Snow wrote:
Just wondering. I'm not gonna try it out. No sense in it. But here it
is: Three 240 volt single phase motors are wired together in delta,
the shafts are connected together in line, and the starting windings
are disconnected. If connected to a VFD, or any three phase source for
that matter, will they spin up? Will they maybe need to be rotated at
assembly 120 degrees to each other? I think it will work. Just idle
curiosity. We all know how dangerous that is.
Thanks,
Eric

No.

An induction motor works because there's a rotating magnetic field that
"drags" the rotor around with it. A 3-phase motor starts automatically
because the magnetic field rotation is unambiguous. A single-phase
motor keeps spinning without the start winding because a single
alternating magnetic field appears to be a pair of fields rotating in
opposite directions, and the rotor generates more torque to the one it's
rotating with than the one it's rotating against. A single-phase motor
needs a start winding (would 90 degrees out mechanically and with some
phase delay electrically) to give an unambiguous rotation to the
magnetic field at the start.

If you put three broken single-phase motors in line and excite them with
three single-phase lines that happen to be 120 degrees out of phase with
each other they'll just act like three broken motors.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com