Re: Need a variable-speed 2hp or greater AC motor for serious gap drive

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Original poster: "Scott Hanson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>

Bill -

One source for relatively well made DC motors in the 1 HP range is from
treadmill exercisers.

All that I have seen are ball-bearing permanent magnet motors with an
oversize bearing on the output shaft, and were in the 3/4 - 11/2 HP range.
Used treadmills can be found very inexpensively at swap meets, garage sales,
etc.

A DC motor in this size range generates unbelievable torque from a dead
stop, and I can't imagine of a RSG rotor that has so much mass or windage
loss that a 1/2 HP DC motor wouldn't drive it perfectly. Remember that the
torque characteristics of a DC motor are very different from a synchronous
AC induction motor. While its possible that a 1/2 HP induction motor may not
have enough torque to get a massive rotor up to speed, even a small DC motor
will, although it may take a little time (think engine starter on a turbine
engine). Actually, you need to use some sort of speed control with a big DC
motor so you can allow the motor to accelerate the load without overloading
couplings, disk hub, disk mounting screws, etc.

Also, there are large number of high-performance, ironless-core DC servo
motors (Servo Disk type) on the surplus market now (ex-computer tape drive
or large disk drive) that can accelerate from a dead stop to over 5,000 RPM
in less than 1 revolution. This type of acceleration can destroy couplings,
etc very easily if the motor is not carefully ramped up to operating speed.
These motors have large diameter shafts, large preloaded ball bearings, zero
shaft end play, and run with almost zero "cogging" from several RPM up to
their maximum speed.

Regards,
Scott Hanson

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----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, June 01, 2003 9:09 AM
Subject: Need a variable-speed 2hp or greater AC motor for serious gap drive


 > Original poster: "W.R. Langston by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <blangsto-at-iwvisp-dot-com>
 >
 > Hello folks,
 >
 > Do any of you have a source for either a universal type AC motor of
between
 > 2 and 5 hp, or a variable speed (chopper-type?) controller usable for a 2+
 > hp induction motor? We need to have built and tested an ASRG for 15-25 kW
 > by July 1st.
 >
 > I suppose a suitable sized, and cool-running DC motor (speed controllable)
 > would work well enough too.
 >
 > We have the machining and structural aspects well enough in hand, but
 > finding a large enough, variable speed motor has proven very difficult.
 >
 > We need to find one or the other asap.
 >
 > Thanks,
 > Bill L.
 >
 >