Re: [CAD_CAM_EDM_DRO] VFD and inverter duty 3phase motors

In a message dated 7/29/2004 10:35:03 PM Eastern Daylight Time,
JanRwl@... writes:

Should I just get a regular ~3450RPM @60Hz motor, and limit my VFD to
60Hz, or should I go for an inverter duty motor where I can run much higher
frequencies/speeds. Any comments would be appreciated.<<
NO! You should get a motor DESIGNED for 400 Hz operation, with fresh
bearings, properly lubricated for that speed. If you go [deleted]ing with a
60 Hz
motor on 400 Hz, even if you DO manage to get the voltage right for that f,
you
will PROBABLY injure yourself! When five pounds of steel (armature)
designed
for spinning at 3600 RPM is spun at 24,000 RPM and the bearings seize-up,
you
are talking major discobobulation! DON'T DO IT! See Perske, etc. BUY one
made for the purpose!



I couldn't agree MORE, regular 60Hz motors are NOT designed to run at high
speed. Not only the bearings but the way the armatures are designed and
manufactured are very different. I would think the first thing to go would
probably be the armature and I personally have seen a motor actually explode when
run around 18,000 rpm and that is 6,000 less than what you could get with
certain inverters.

DO NOT USE A 60 HZ MOTOR EVEN IF IT IS INVERTER RATED. The purpose for
inverter rating a 60Hz motor isn't so it can run at a very high speed, but
actually so it can run at a much lower speed. When you run a regular asynchronous
AC motor at low speeds it will get hot because there isn't enough cooling air
going over it due to the slow speed of the cooling fan attached to the
shaft. In an inverter rated motor the windings, insulation and sometimes the fan
are different and designed for this situation. In some cases they may even
attach a single phase electric fan to the end of the motor for cooling at
lower speeds.

Hope this helps.

Randy Abernathy
4626 Old Stilesboro Road NW
Acworth, GA 30101-4066
Phone / Fax: 770-974-5295
Cell: 678-772-4113
E-mail: Cnc002@...

I furnish technical support, repair, and other related services for your
industrial woodworking machinery. My background as Senior Service Engineer for
the SCMI Group for nearly fifteen years with factory training, combines with
my extensive background in electronics, mechanics, pneumatics, electrical and
CNC machinery to offer you needed support for your machinery.


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