PDA

View Full Version : running an EDM on single phase with a VFD



jim davies
12-17-2010, 11:28 PM
Got a chance to get an Eltee Pulsitron for a good price. Problem is it's 3 phase and my shop is a long way from 3 phase power. I have been advised by Driveswarehouse that a VFD will not work for this application. Anyone know why? And is there any other way to do it?

squirrel
12-17-2010, 11:43 PM
They are 100% correct.

You will need a Rotary Phase converter. The best one to get is made by American Rotary and they use a special motor built by Baldor. I have designed these things and bought a few for analysis and the American Rotary is the only one that has correct phase alignment and voltage. I am not affiliated or endorsing their product, just stating my experience.

lakeside53
12-18-2010, 01:35 AM
I can see the specialized baldor motor may output better regulated voltage on the wild leg, but why is their phase alignment any different to stock motor used as a rotary converter?

OP - the why is that it's not just the motor that requires three phase -there are electronics that require a three phase input. The VFD is a motor drive; not a general purpose three phase source.

squirrel
12-18-2010, 11:33 AM
I can see the specialized baldor motor may output better regulated voltage on the wild leg, but why is their phase alignment any different to stock motor used as a rotary converter?

OP - the why is that it's not just the motor that requires three phase -there are electronics that require a three phase input. The VFD is a motor drive; not a general purpose three phase source.
Its a high slip motor, a parameter that is undesired when you are looking for maximum energy efficency. If you can get an old 1950's era motor and build your own it will perform better than one made from a late model energy efficient motor. Any rotary will work fine powering another motor, however depending upon the desgn of the power supply in the EDM you could create problems.

Many dooms day scenerios exist and more time is waisted worrying about them, so its better and safer to start with the best and cleanest power source you can provide. Many of the replacement boards for a machine will cost more than a quality rotary.

JRouche
12-18-2010, 02:11 PM
The best one to get is made by American Rotary and they use a special motor built by Baldor. I have designed these things and bought a few for analysis and the American Rotary is the only one that has correct phase alignment and voltage. I am not affiliated or endorsing their product, just stating my experience.

Yup. Don't know if they are the best. But I do know they are good. I have built a few RPCs, they are pretty simple. Many detailed plans available online.

But for my Emco cnc lathe I needed some really good filtering. These lathes are known to be finicky about the supply power. Not like my bridgeport cnc, its on a home grown 5hp rpc and works just fine.

I bought a 15hp hd/cnc rpc from american. Not cheap, but pretty darn nice. JR

I did some checking of the line voltages when I got it. Some talk about that here.
http://www.practicalmachinist.com/vb/transformers-phase-converters-vfd/15hp-rpc-emco120-cnc-lathe-review-long-winded-102474/

Oh, and its quiet..
More on that here.
http://www.practicalmachinist.com/vb/general/quiet-phase-converters-144351/

http://img.photobucket.com/albums/v366/Jrouche/PM%20site/splrpc3.jpg

http://img.photobucket.com/albums/v366/Jrouche/PM%20site/splrpc2.jpg

jim davies
12-18-2010, 08:21 PM
Thanks for the help on this. So an RPC will solve the problem? I also have a 2HP lathe and mill and a pair of 3 phase motors. What size RPC should I look for to work with them and the Pulsitron.

Apparently it is about 35 amps output.

squirrel
12-18-2010, 10:00 PM
I would size it with a 20 hp idler.

lakeside53
12-19-2010, 02:48 PM
35amp EDM output? A 2hp here and there.. 20hp is huge....

What's the edm input requirements? voltage and current / va?