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?



Yes, it most certainly could. All it needs to do is reverse the
RELATIONSHIP of the feild and armature.




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