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Rayatswan
11-24-2012, 06:15 PM
I recently purchased a lathe and it has a Toshiba 3 phase 50hz 3.7kw 4 pole motor in it. I was going to convert it to run on 240v and build a rotary phase converter to drive it but when I pulled the terminal cover off there are only 3 wires, any Ideas on how to check if it can be converted to run on 240 volt.... Thanks

darryl
11-24-2012, 09:06 PM
VFD is the obvious answer. No change required to the motor, and you get speed control and probably braking as well. In your case, the VFD would be selected to run from 240. You would need to know what voltage the motor is designed to run on.

Rayatswan
11-24-2012, 09:59 PM
Sorry, should have written that the motor is 415v currently.

darryl
11-25-2012, 01:14 AM
Hmm- that shrinks the choice of VFD. I have no idea what might be available to handle that voltage- out of my league here.

The Artful Bodger
11-25-2012, 01:25 AM
What is your local power supply? In other words, where in the world are you?

Rayatswan
11-25-2012, 02:48 AM
240V, your neighbour in Australia

The Artful Bodger
11-25-2012, 02:53 AM
Ok Ray, I think you are in Australia?

It seems you need a step up transformer to get that 240 volts up to something nearer the desired 415 volts then you build the rotary phase converter. An alternative is to make a low voltage rotary phase converter and use a transformer for each phase (or a three phase transformer).

You could use a 'rotary transformer' by building a rotary phase converter using a dual voltage 3 phase motor.

Google "rotary phase converter site:au", that will hopefully get your results relating to Australia, or do the same with "site:nz" as we have pretty much the same electrical environment.


OK Ray, I see you just answered me!

The Artful Bodger
11-25-2012, 02:54 AM
Have you got any isolation transformers? The ones they used to use on building sites?

Rayatswan
11-25-2012, 04:13 AM
No I dont have any isolation transformers, I was hoping some one could tell me an easy way to tell if its worthwile opening up the wire connections to check if its star wound and then change it to delta for low voltage use,

The Artful Bodger
11-25-2012, 04:18 AM
Well, I was going to tell you how to run it on a 240v rotary phase converter without modifying the motor.

If it is 3 phase and only has three terminals you need to check how many connections there are to the back of each terminal, one coil connected to each terminal indicates star connected and you can expect to see a three way splice somewhere in the motor, if delta connected there will be two coils connected on the back of each terminal.

Assuming it is star connected changing the motor to delta requires finding the point inside where all three windings are joined together. Split those apart and reconnect for delta.

EVguru
11-26-2012, 04:47 AM
I recently purchased a lathe and it has a Toshiba 3 phase 50hz 3.7kw 4 pole motor in it. I was going to convert it to run on 240v and build a rotary phase converter to drive it but when I pulled the terminal cover off there are only 3 wires, any Ideas on how to check if it can be converted to run on 240 volt.... Thanks

Been there, done that, re-posted this many times;

http://bbs.homeshopmachinist.net/threads/39602-Motor-rewire?

Rayatswan
11-26-2012, 03:06 PM
I pulled the motor apart today, here are some photos of what I found

http://i993.photobucket.com/albums/af51/rayatswan/034.jpg

http://i993.photobucket.com/albums/af51/rayatswan/036.jpg

Here are the Star connected wires exposed and ready for connection to 3 new wires.

http://i993.photobucket.com/albums/af51/rayatswan/038-1.jpg

EVguru did you use heat resistant wire, where did you get the insulation that you put over the soldered joints and what did you use to re tie the windings?, any help is appreciated.
I also am glad I pulled the motor apart as one of the leadout wires has broken down insolation and could have caused a short.