Bringing this back up as I too just got a 2 speed 3ph motor for my mill and will be using a VFD on it.
Here is what I am thinking........
My motor has 6 leads.
For low speed VFD lines go to leads 1,2,3 and leads 4, 5, 6 are disconnected.
For high speed leads 1,2,3 are connected to each other and VFD lines go to leads 4,5,6
Was thinking you could do this with three 3PDT swithches - two for the 6 leads and one for the motor leads from the VFD.
Then was thinking why not have three 3PDT 24V coil relays controlled by the VFD outputs.
Relay #1 is the VFD motor-out leads
Relay #2 is Baldor motor leads 1-3
Relay #3 is Baldor motor leads 4-6
Wiring:
NC 3poles of Relay #1 go to NC of relay#2 and NC of Relay #3 is left empty.
NO 3 poles of Relay #1 go to NO of Relay #3 and NO of Relay #2 are joined together
Then you set up motor setup #1 to not do anything and it will keep all relays open/un-latched and the motor will be setup for the slow speed range
Then you setup motor setup #2 (maybe enabled by a switch?) to latch the coils and the relays will setup the motor output for the fast speed.
Just typing out loud. What do you think?