On Thu, 18 Mar 2004 18:34:08 -0600, "Bob Swinney"
wrote:

Brian,
The "speed" of reversing a 3-phase motor would be a function of how stiff
the 3-phase source is. A genuine 3-phase line being the quickest. I have
done this and it is hard to tell when stop-then- reverse occurs. It is
about as close as you can get to instantaneous. Following, I would guess,
is a good stiff, balanced, rotary phase converter such as the 25 HP one you
propose. Though I've not tried reversing with a VFD, I believe the smaller
the power rating of the VFD, the longer it would take to reverse a 3-phase
motor.

Bob Swinney

Just curious, what do you use instantaneous, as opposed to fast,
reversing for in machining (I'm still a newbie)? Also, is there any
electrical downside to really fast reversing on either a converter or
vfd? I have a L-00 spindle, so I'm not overly concerned with sending
the chuck across the floor.

Regards,

Pete


"Peter T. Keillor III" wrote in message
.. .
On Thu, 18 Mar 2004 07:51:58 -0500, Brian Lawson
wrote:

On Thu, 18 Mar 2004 06:55:28 -0500, Peter T. Keillor III
wrote:

On Tue, 16 Mar 2004 15:57:06 -0800, "Paul"
wrote:

SNIP

I like vfd's, but wouldn't argue with the guys building converters
from low cost or free motors. But for that price, I would have gone
for a vfd.

Pete Keillor


Hey peter,

I thought there was at least some controversy about being able to do
"instant" reversals with a VFD attached. Any comments from anybody?

This comment/question from somebody who hopes to be starting a 25HP as
a rotary convertor some day pretty soon.

Take care.

Brian Lawson,
Bothwell, Ontario.

Brian, I don't know about instant, but you can do 'em pretty quick.
It depends on how you program the accel and decel times. I don't need
fast, so I set mine for 10 seconds. When I flip from forward to
reverse, the motor decelerates to a stop, then instantly changes
direction and accelerates in reverse.

Update: I just went in the shop and programmed 1 sec. accel - decel
times. It changes direction damn quick.

Pete Keillor