RE: SRSG motor power

["John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Gomez -

Wind loading and starting torque are standard problems for people designing
motors. Look up an Electrical Engineering Handbook.
The problems are somewhat complicated. For example, the windage equation is

   Watts loss = 3 * K * D^3 * RPM^2
   D = rotor dia in inches
   K = Factor that varies with different motors

John Couture

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-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, July 28, 2000 6:07 PM
To: tesla-at-pupman-dot-com
Subject: Re: SRSG motor power


Original poster: "Ed Phillips" <evp-at-pacbell-dot-net>

Tesla list wrote:
>
> Original poster: "Gomez ADDams" <gomez-at-netherworld-dot-com>
>
>  I am in the process of building a massive multiple-series SRSG for my
next
> big coil project. (24" secondary, ~24kW in)
>
>  I haven't been able to come up with much information for calculating the
> "wind" loading of the rotor, or the recommended motor starting torque for
a
> given mass/moment arm.

	Somewhere in my archives I have an old (1930 era) NACA monograph on
this exact subject.  Have been looking for it for a year now, so far
without luck.  What I do remember is that the torque varies as the cube
of the rotation rate and the FIFTH power of the radius!  I was once
involved with an experiment which called for rotating a 36" diameter
solid disk at 3600 RPM.  We started with a 5 hp sync induction motor,
which didn't have enough pull-in torque to run synchronously.  Finally
got the thing to run by putting a mercury clutch between the motor and
the wheel, but the windage was such that the wheel actually turned at
about 3300 RPM.  At this speed it pumped an astonishing amount of air!
Tried running it in a wooden/paper container of Helium to reduce the
windage, but that was a spectacular failure because, as the wheel came
up to speed, it sucked the container in at the center where the pressure
is lowest, causing it to actually adhere to the wheel.  At that point
things got really interesting because the framework got caught in the
edge of the wheel and stuff flew all over the lab.  No one was hurt, but
thereafter we ran it in air......

	One thing which might have helped but which we weren't in a position to
try would have been to momentarily over-voltage by perhaps 30% during
startup.

	As already posted, the setup you propose should work fine.

Ed