Re: [CAD_CAM_EDM_DRO] Re: hi-freq motors[perske etc]

Hi, some of the wood shops around here have used moto-gen sets for speeding
up spindle speeds. i have seen 400,800,1200 and 2000 hertz for
frequency....if you take a suitably made motor(small diameter but long in
the iron)such as the spindle for a wood heel shaper it turns 2,3 or 4 blades
of hss steel some are 5 by 7 inches 1/4 thick on the 400 hz the motor
produces 3 1/2 hp however switched to 1200 hz that same motor makes 10 hp at
10,000 rpm! some of those spindles ran for 40 years before needing to be
rewound. The wood shop in Vermont used 3 diesel engines and the first turned
up to 120 hertz, the second at 400hz and the big one at 800 hz. it was weird
to hear them start the hi speed spindles on 120, then shift to 400, then to
800 hz. then they would shut down all but the 800 hz
diesel(600 hp) and that ran all day. if they shut down a spindle they would
restart it with a universal motor and a round belt untill it would go back
on line. By the way these hi speed spindle motors are built much like a
permagnet stepper only the armature are wrapped in kevlar + etc.balanced for
the job. cul brian f.

----- Original Message -----
From: <JanRwl@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Thursday, November 22, 2001 4:47 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: hi-freq motors[perske etc]


In a message dated 22-Nov-01 09:16:16 Central Standard Time,
shymu@... writes:


> What is the reason for using hi-freq motors/spindles ?
>


Frank: Undoubtedly, someone knowing much more about "AC machines" will have
answered this more properly before MY response appears, but here goes,
anyway:

The rotary speed (RPM) of an AC motor depends upon line-FREQUENCY rather
than
voltage. The voltage has to be "right", but, for example, raising the
voltage on a 240 VAC motor to 300 VAC will only serve to cause its rapid
destruction and discoloration, though a just-perceptible increase in
"available torque" might have been available for a (very) short time after
so-raising the voltage.

HOWEVER, if you raise the FREQUENCY from 60 Hz to, say, 120 Hz., you will
DOUBLE the RPM of that motor, assuming it "can take it", and there is no
mechanical load which will preclude this "over-speeding". (The HF motors
are
DESIGNED for that, and the VOLTAGE is engineered to fit in with the HF, as
well).

Now, if you raise the AC-frequency to 400 Hz., you will have a motor
spinning
at either 12,000 or 24,000 RPM (depending on how the AC motor is wound,
inside). But the amount of copper is often reduced, etc., so a "400 Hz
motor" can't be run on some much-lower F, like 60 Hz, without cooking, etc.

But most utility-companies in the U.S. sell us only 60 Hz. power. One needs
a "power converter". Forty years and more ago, this was done "only" with a
motor-generator, a big ol' boat-anchor that looked like a longer-than-usual
electric motor with NO shaft coming out either end. But TWO "terminal
boxes"
on the side. One is for 3-phase AC in (240 or 480 V, 60 Hz), and the other
is for 400 Hz. out. The voltage-out depends entirely on the manufacture and
the agreement with the customer purchasing same, hopefully correctly chosen
to match that of the HF motor to be powered therewith. Now, some uses can
be powered with a "static freq. converter" which is a "black box" (often
"machine-green" or grey, etc.!) which "electronically converts" the power
for
you, with NO rotary converter ("motor-generator"). The new VFD's can do
just
that, Vary the Frequency, and Drive the motors at various speeds, though I
am
guessing only within a "practical range", due the the fact that the VOLTAGE
requirement of an inductive device like a motor varies considerably as the
Frequency varies! (Takes some elec.-engr. smarts I ain't got!)

Now, say you have just bought-in a 3½ hp. 400 Hz. 3-phase Perske
router-motor, with a "to suit" motor-generator, and decide to wire it all
up,
temporarily, "just to see", before you install these items on that new CNC
machine you are building: MAKE SURE you have BOLTED 'em down, at least with
some VERY-heavy and new Jorgenson clamps, cause, when you switch-on
"shop-three-phase" to that lashup, your ZIP-CODE will change! And, you do
NOT want an unmounted motor-generator spinning across the shop-floor, due to
Newton's laws, when the armatures inside begin to spin!

Lotsa luck! Jan Rowland, Troll


[Non-text portions of this message have been removed]


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