Re: [CAD_CAM_EDM_DRO] What variable speed motor to use?

I've been asking a few questions of this forum, maybe its time to contribute
a bit.

I've recently converted two machines to variable speed operation. I put a
variable frequency drive on a 1.5 HP 3 phase milling machine and removed a
single phase 1 HP motor from a large drill press and put on a 0.75 HP 3
phase motor and Variable Frequency drives.

IMHO, anytime I want variable speed motors, I go find a cheap 3 phase motor
and buy a good, inexpensive VFD. Here is a link to my favorite one:

company: http://www.kbelectronics.com/

product: http://www.kbelectronics.com/catalog/gc115/kbvf.pdf

The KBVF is rated to run 1 HP 3 phase motors in a near zero air flow
environment. I spoke with the engineers and they said it will run 2+HP with
a fan on it.

These units are very versatile, tough and inexpensive. I paid C$225 (about
US$ 150) for our VFD units. Small 3 phase motors are cheap around here.

The great thing about this combo is that the motors will run cool at low
RPMs and still develop good torque. Furthermore, I don't have to fool
around with DC power supplies. These controllers will output 120 Hz power,
allowing a 1725 motor to run at 3400 RPM. My next candidate is going to be
my lathe because its top gear is only 1100 RPM. I turn a lot of small stuff
and it would be nice to run at 1500+ RPM from time to time.

Someguy.

----- Original Message -----
From: <ccs@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Thursday, October 18, 2001 7:32 PM
Subject: Re: [CAD_CAM_EDM_DRO] What variable speed motor to use?


>
> > Lee,
> > The "treadmill motor/controller" set sold at Surplus Center
> > 800-488-3407 p/n 10-1806 at $49.95 (No web site)
> > is a great choice for this. I have a drill press and a Bridgeport
> > mill converted to DC and love it.
> > These are industrial 90VDC PM units with full speed range and feedback
> > for torgue. You will have to fab a mounting method as the frame is not
> > standard.
>
> If I remember correctly the treadmill motor develops its maximum power
> at a substantially higher RPM than the typical 1725 rpm of the typical
> 60 hz AC induction motor typically used on a machine like this.
> Variable speed motors aren't great at putting out torque far below
> their designed speed. What I think he really needs is some more reduction
> between the motor and spindle.
>
> But maybe someone has had acceptable results with the treadmill motor and
no additional reduction.
>
> Chris
>
>
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