On Mon, 19 Sep 2005 19:56:56 GMT, JohnF
wrote:

I have no clue what a 4 quadrant drive is. It's an old Reliance 480v 3
phase drive with a large bank of rectfiers and a rather nasty
contactor (1). I don't understand exactly how it reverses itself
unless it switches a bank of diodes to change the +/- of the motor
input or could it do it by changing the +/- of the field windings?







On Thu, 15 Sep 2005 19:51:50 -0500, Jon Elson
wrote:

Leo Lichtman wrote:
"JohnF" wrote: (clip) Could it be as simple as switching the 2 motor leads?
^^^^^^^^^^^^^^^^^
On a motor with permanent magnets for the field, it would be, but a motor
that large is going to have a wound rotor and a set of field windings.
Reverse either, but not both. If you reverse the connections to the
brushes, that should do it.


Yeah, that sounds like the best plan. A 40 Hp motor is going to have
commutating poles, and how you set up commutating poles on a reversible
motor gets complicated. Normally, I'd expect something like this to
just have a pair of big contactors to handle the reversing. Was this
a 4-quadrant servo drive? That's about the only reason I could think
of electronic reversing of a motor this size.

Jon

In order to reverse the rotation of the drive the armature leads as
well as the field leads need to be reversed, also the tach leads.

Direction of the motor is determined by the polarity of the armature,
the large contactor is just the the loop contactor and only comes up
when the drive is enabled.

One thing you may try is just reversing the speed command the +-10vdc
velocity signal from the cnc.

The manual for the drive is very clear about how the spindle rotation
direction is determined.

You have to be very careful as the motor will run away and cause you
heart attack.

Regards


Daveb