Brian Lawson wrote:

Hey Guys, and Fitch (I hope),

OK....my turn for Questions and Answers (hopefully) on the rotary
convertor I'm about to attempt to hook up.

First.... the question.... I have a 3 phase wound rotor motor to use
as a convertor for 220VAC single phase to 220VAC three phase. How do
I "hook up" with this? Do I short-out the slip-rings and just
consider it a squirrel cage, or do I wire to both the rotor and
stator, or wire to the stator and take the three phase off the
slip-rings (actually I don't think THAT works), or.....or....or????
..................................................

Now for the description, for those that are still reading.
Long-winded, as usual, but it helps me out to do so. Sorry.

I was fairly recently blessed with two freebie 20HP motors. Except,
different to any earlier postings here that I recall, these are wound
rotor motors.

These were in use on AC geared traction elevators, and were wired for
"Dynac" use, which is a 1960's method of getting speed control almost
like a DC operation from AC motors, using some special mechanical
features and controls and incorporating either 2 or 4 medium size
thyratron tubes. Gladly get into details for anybody that wants, but
this is merely explanatory/descriptive here as I won't be using any of
that mode.

The motors were made by Bull Motors, England, as 208 VAC, 3Phase,
60Hz, 1150 RPM, 67 Amp, all copper windings. One pair of 1/2" X
5/8" brushes on each slip-ring. One of the two motors has had the
stator redone locally fairly recently (and that's the one I want to
use), and in the external junction box it just has three stator lead
connections ,and three direct to the slip-rings connections for the
rotor. The second motor has some BAD gooey rubbery disintegration of
the 3 of the wires as they feed through the motor frame to the stator,
and so I don't want to use this motor; BUT.. it has a small Bull
original print diagram in the junction box showing that the motors had
9 leads... 3 to the slip-rings for the Delta connected rotor, and 3 to
the STAR stator field pieces and 3 connected together to form the
STAR. I assume that the STAR shorted leads are done internally on
the rewound motor I hope to use..

These motors are fairly beasty things, with about a 20 pound flange
coupling still in place on a 2-3/8" rotor shaft turned down to 2" for
the coupling. I may well cut the couplings off later, but I can't
pull them in situ here without a largish puller. And I've wondered,
and maybe somebody can tell me, if the heavy coupling would actually
assist in strengthening the output after reaching full RPM. If so,
would heavier be even better? I can pour lead in to do that!. In
original operation, this flange was coupled to a special 20" diameter
X 12" long brake drum with1" thick flange with the external diameter
having pressed in copper bars through it parallel to the motor shaft,
so they were pretty heavy and added a lot of inertia "smoothing" to
the speed variations in operation.

Any suggestions? Or do I still need to call Marty for the rotary he
has for sale????

The 3 leads from the wound rotor would normally go to a
starter/speed control box. The box would have a sequence
of resistors that would be inserted between the leads
coming off the rotor, with maximum resistance for starting/
slowest speed and zero resistance for max speed.

The difference between starter service and speed control
service is that for speed control, the resistors have to be
able to dissipate heat on a continuous basis. For starting
service, they are rated for intermittent duty and don't have
to be as big, wattage wise.

I don't have a clue as to what a good starting resistance would
be. If I were doing this, I'd probably try 100-200 watts
of light bulb for each resistance to see if it would start.

I can check my books at home tonight. I have an old Audel's
book on elevator controls and it might have more information.