2 speed motor of VFD - check my reasoning plz

I have bought a machine which has a 3 phase 2 speed motor and I don't have 3 phase power but I also don't want to replace the motor - I want to power it from a VFD which outputs 240v 3 phase. I've got the wiring schematic and figured out that it's a pretty standard 6-wire setup that switches 3 of the wires to be a star point and convert the 4-pole motor to a 2-pole for high speed. Here's the layout:



What I want to do is re-configure the motor to run at the slow speed from a VFD (which is 240v output instead of 415 original supply). Online research suggests that if I run the motor in delta mode same as the slow speed schematic above, but split the two windings and wire them in parallel instead of series, that will be the appropriate configuration.

My plan is to disconnect each pair of windings at the mid-point between phase inputs, one at a time so that I don't make any mistakes, and re-connect them in parallel like this:



If I do one at a time I'm pretty certain that this will keep the winding orientations correct but what I'm clueless about is will it give me the 4-pole 240v motor that I'm expecting or will that not be so? I don't mind giving it the 'suck it and see' approach but I thought I ask right here in case there is something fundamental I am not considering.
BTW I get the machine home next weekend so right now I cannot pull the motor, I'm at planning stage for doing this work right now. I've got the VFD ready to go and the wiring is no problem for me.

What do we think? Is it just as simple as that?

Pete.

Try and make the first image larger. It too small for me see.

In a recent thread rootboy posted a link to a youtube video which may be helpful for you. It is very well done, and through enough that it ended up being 4 video's. It shows how to make a RPC which runs off of 240 volt single phase and generates 415 volt 3 phase. I know this is not what you are asking about, but it would allow you to use the lathe and motor as designed.
There also may be something in his description and diagrams which would answer your question.

Rotary phase converter - UK - Part 1, Intro. - YouTube

J_R_Thiele said:

Try and make the first image larger. It too small for me see.

Click to expand...

Must have auto-resized the original is 1024x768

From the details of the switchgear, this is a consequent pole motor. The typical approach to running these from a VFD is to hard-wire them into the high speed configuration, and connect your drive directly to the motor leads. This means three leads will be shorted together and three will go directly to the drive. (green lines on your diagram are the shorting connections for high speed).

On edit: the original post was not clear, is this a 415 volt designed motor, or a 240 volt designed motor?

It's a 415v motor Jim.

Your approach might work but I've never seen it done - the windings are basically a ring so you might have some trouble digging out the leads to put them in parallel. If it does not work of course you could always put it back. Any chance for a re-wind from motor shop?

jim rozen said:

Your approach might work but I've never seen it done - the windings are basically a ring so you might have some trouble digging out the leads to put them in parallel. If it does not work of course you could always put it back. Any chance for a re-wind from motor shop?

Click to expand...

Well thee's nothing special per se about the motor except it's housed within a machine and it's a slightly over-sized open frame motor of good quality, so if it doesn't work I always have the option of replacing it.

I will atempt to open it up and re-configure the windings, and report back with my results.

Thanks
Pete.

There is no need to do anything to the motor, just get one of these VFD 2.2KW single phase to 3 phase inverter 220v to 380v variable frequency drive converter|Inverters & Converters| - AliExpress or one of the larger models if the motor is over 3HP.
I use one on a 2 speed (double Star) motor on a German cold saw.

jim rozen said:

Your approach might work but I've never seen it done - the windings are basically a ring so you might have some trouble digging out the leads to put them in parallel. If it does not work of course you could always put it back. Any chance for a re-wind from motor shop?

Click to expand...

This turned out to be providential. The motor had one lead open-circuit and I found the break easily enough as it was only 2" from the terminal but the insulation is so delicate that the varnish was flaking even with gentle manipulation. I have abandoned the idea in favour of fitting a more modern motor on an adapter plate.

Thank you to everyone who offered their input.

As a follow-up I'd like to report that I didn't give up on this motor. What looked like impregnable insulation was actually quite easy to break away from the widings, which remained undamaged. I found all of the ends easily accessible under the wrapping, brought them out and linked them as in the diagram in post #1. I re-bound the windings, gave it two coats of winding varnish and a few days to dry and it's now up and running on a cheapo inverter whilst I wait to get hold of a branded unit.