Changing a Motor from Star to Delta

I'm hoping that one (or more) of our electrical boffins can help me with this one.

I have done this task successfully where there have been links to remove and replace but I've now come across a different system.

The motor is a Brook Crompton Parkinson 1.5kw one and normally sits in the base of a Tom Senior Major Mk 2 ELTmilling machinel.

I eventually managed to remove the motor which has a plate stating that is is 220/380-420 volts and alongside this are the Delta & Star symbols.

When I opened up the junction box on the motor I found 4 terminals plus earth.

3 of the terminals were for the individual phases with one black wire to each from inside the motor.

The other terminal had 3 black wires from inside the motor all connected to the one terminal.

I have a 240v 3 phase inverter rated at 1.5kw, how do I connect it to the motor?

Any help will be most welcome!

Brian

Aha! You need to...

• remove the 3 black wires from the common terminal
• don't remove any of the other wires!
• identify which of the wires you just removed are the other ends of the connections to the other terminals. Suppose the other terminals were 1a, 2a, 3a, they would be 1b, 2b, 3b.
• connect 1b to 2a, 2b to 3a, 3b to 1a
• You're done.

Brian

The 3 black wires on the same terminal will be the ends of the windings, if there are no markings at all you will have to identify the pairs of windings so you can connect in delta mode.

If you have an ohm meter you can remove the 3 wires and separate the ends, then check across the end of 1 and find it's mate still connected on the terminal block, mark the 2 with some number so you know they are a coil.
Do the same again with 1 of the other 2 free ends, then check the remaining 1 just to be certain you have 3 coils, all coils should be the same resistance within a few ohms.

If someone doesn't beat me to it I will post a drawing on further connections and links.

Emgee

John beat me to it again so follow his advice.

Edited By Emgee on 04/11/2019 18:29:52

Many thanks John & Emgee. I've now cleaned the areas and can see that there are tags on the wires.

The wires on the individual terminals are marked U1, V1 & W1. The 3 wires on the other terminal are marked U2, V2 & W2.

I have dismantled the motor further and found that the bearing just behind the pulley is siezed and have removed this. It is marked 6205Z which I know is an easily obtained one. I'm assuming that the other bearing will be the same but will remove the nylon fan and end cover to check. Any suggestions on removing these without damage?

Brian

Hi Brian, I may be telling you what you already know but To reverse the rotation just swap any two incoming phases. Though if your using an inverter then this may not be needed.

Good luck, Noel.

And then-- When ordering the bearings tell the supplier that there for an electric motor and likely will be C3 fit.

Noel.

Many thanks Noel, yes, I knew about swapping 2 wires and the bearings I've ordered are C3 but I'm very grateful to you for replying.

Brian

Just to confirm that I have understood correctly.....do I then connect each of the phases from the inverter to the same terminals that I connect both ends of the coils to?

Brian

I had a Brook Crompton three phase motor on my Elliot Omnimill and after rewiring from star to delta I ran it on single phase with just a capacitor between two of the phases. You only get about 80% of the rated power but I never noticed the mill struggle.

Brian

U1, V1 and W1, the original terminals that were connected,
ignore the lettering on the 2's you removed from the other terminal.

Emgee

Emgee, I'm not quite sure what you meant to say there, but I'm not sure it came out right in print.

3 individual windings U, V, & W, each with ends 1&2 and all end 2s currently commoned together in Star formation.

To transform to Mesh (i.e. Delta), whilst still maintaining the correct orientation of each coil, as follows.

Leave U1, V1, & W1 where they are, U2 goes on top of V1, V2 on top of W1, and W2 on top of U1

The three phases go to each of the three terminals ( which now have 2 wires on each one)

To reverse the motor, swap any two phases (not windings)

Bill

Bill

Sorry Bill, I apolpgise for my bad description, yes you only have 3 terminals and 3 incoming wires to connect so 1 phase on each is the only option.
As said for reversing swap any 2 supply cables, no doubt easier to do at the VFD.

Emgee

So, please excuse me for being pedantic but;

Quote Leave U1, V1, & W1 where they are, U2 goes on top of V1, V2 on top of W1, and W2 on top of U1

The three phases go to each of the three terminals ( which now have 2 wires on each one) End of quote

So the end of one coil is connected to the start of the next coil?

Brian

Hi Brian that is correct the end of one coil is connected to the start of the next

Mickyt

Thanks for clarifying Mickey, and thanks to all who replied.

Wonderful Forum this!

Brian

One can consider it as connecting them in series, but being careful that each coil is pulling in the same direction as the others. What one does not want is one coil connected such that it is opposing the the other two!

A picture can be worth a thousand words.

Mike

Edited By Mike Poole on 05/11/2019 13:42:06

Many thanks Mike, that very helpful.

Brian

Brian, nice clear detail in Mike's picture, are you up and running now ?

Emgee

Been there, done that. Eventually sorted it out.

Edited By Brian Oldford on 05/11/2019 17:27:56