View Full Version : building 3 phase convertor, Quick Question???

11-18-2004, 07:39 PM
I am in the process of gathering the materials to build a 3 phase convertor for my shop. The question is does it matter much on the RPM's of the 3 phase motor used in the convertor? I have a new 5 hp motor that is 1800 rpm's. I also have a good used 5 hp 3450 rpm 3 phase motor. Which one will work best? or does it matter?

Steve Steven
11-18-2004, 08:17 PM
I am not an expert, but I don't think it matters much. Both will work, but the 3600 RPM one would have more windage losses and inertia to overcome, so I would think the 1800RPM one would be better. The 3600 RPM motor is a two pole motor, the 1800 RPM one is a four pole one.

11-18-2004, 09:07 PM
I just built one this summer lots of good info on the net. By what I have read an older inefficient motor works the best and lower RPM is better.

I built a 7.5 HP converter for a Bridgeport series 1 cnc works great. http://bbs.homeshopmachinist.net//biggrin.gif

11-21-2004, 11:33 AM
I build my first rpc within the last year.

It seems to me that there was something about high rmp idle motors having the advantage of a more correct phase angle. But, they are harder to get going. You wont pull start a high rpm motor very easy. You would need a pony motor or a timed capacitor start of some sort.

There is a lot of information on rpc's on the net. And in these groups. Here are some links that I used while making my converter. Hope that they help.


And a great resource http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif
This Fantastic BBS! (http://tinyurl.com/4gl7m)

[This message has been edited by rockrat (edited 11-21-2004).]