"JohnF" wrote in message
...
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?


As far as I know, Reliance drives starting from the mid 70's use SCR's
connected to the 3 phase lines (as do GE drives) for armature voltage.
There is a separate module for field excitation.

Is this a MaxPak series drive?