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MMD > Archives > January 2003 > 2003.01.15 > 10Prev  Next

Mills Violano AC/DC Rotary Converter Patents
By Robbie Rhodes

I telephoned Mike Ames today to ask if he knew the patent numbers
of the Mills converter.  He found them on the brass label of the
machine, and I quickly retreived images of the original patents
from the U.S. Patent and Trademark Office (USPTO) web site,

Images of the 1921 and 1923 patents by inventor Henry K. Sandell
on his "Dynamo Electric Machine" are now available at the MMD Tech
site at

According to the 1923 patent description, the machine is essentially
a 4-pole self-excited DC generator, powered by an integrated 4-pole
split-phase AC induction motor with auxiliary starting winding and
centrifugal starting switch.  The motor is "inside out" as compared
to a normal induction motor, since the winding is on the rotor instead
of the stator.  The AC starting current also flows through a stator
winding, which implements one of Sandell's patent claims.

Assuming the starting winding or switch isn't damaged, the rotor
will spin the same direction each time it starts.  If the starting
switch is bad or the start winding is open, then I suppose the rotor
just sits there and hums and overheats, just like tired motors
in orchestrions.

D'ya remember long ago when we bought a rebuilt generator for the
old 1939 Ford or Chevy?  The paper tag said to "flash" the field with
battery current before use, because most likely the residual magnetism
had been degaussed during testing.  The flash of current was to give
the steel stator (the field magnet) a bit of residual permanent
magnetism of the correct polarity.  Then it would start generating
with the correct polarity.

The generator field electromagnet of the Mills converter is the steel
stator, which probably retains some magnetism after shutoff, but the
winding carrying 60 Hz AC starting current also runs throughout the
stator.  Thus the stator is thoroughly degaussed during starting.

An oscilloscope observing the DC output would show 60 Hz AC, phase
modulated by the rotor position, until suddenly regeneration takes
effect at random polarity and the DC voltage builds up quickly.
Sandell doesn't mention this randomness "feature" in the patents.

Craig Smith asked: "Mike, what would happen if someone decided
to reverse the polarity on a MIDI-fied Violano?"

Mike's succinct reply: "Smoke!"

Robbie Rhodes

(Message sent Thu 16 Jan 2003, 03:18:16 GMT, from time zone GMT-0800.)

Key Words in Subject:  AC, Converter, DC, Mills, Patents, Rotary, Violano

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