OT - Phase Converters (Build Your Own)

There have been several questions and threads about running machines with 3-phase motors when only single phase power is available from the lopoco (LOcal POwer COmpany). I chose to go with a Rotary Phase Convertor (RPC) and also decided to build one myself rather than purchasing a one. Right now, on Ebay, you can buy a 15 HP phase convertor for about $1200 (plus shipping). It's probably going to cost me in the range of $500 to build mine.

So - how do you do this?

The best place to start is a forum called The Practical Machinist. There is a subforum dedicated to Phase Convertors and VFDs. Why there? These boys and girls like to play with metal-working machinery which is typically 3-phase.

There is a boatload of information in that forum about motors, VFDs, phase convertors and the like. The forum is moderated by someone who is very knowledgeable about RPCs and has posted schematics. My design is something that will eventually be posted there (it's an adaptation/extension of a basic one Bob did), but it's not in electronic format yet.

This forum is an excellent place for anyone to start who is interested in running 3-phase machines at home. It will take you weeks to read and digest the information in there.

One comment - if you're interested in building your own RPC, don't try to shortcut the process by just getting a schematic and plugging things together. You need to understand a little bit more about what you're building. The type of power a RPC generates is called "high-leg delta" and the generated leg has a voltage to ground of up to 208 volts (phase to phase is still 240v). Needless to say, that can give you quite a kick in the pants if you touch it.

As the HP rating of your idler motor increases, so does the complexity of the switching gear. If you only want a small, 1-3 HP RPC for a drill press or similar, the switches and stuff can be normal motor rated switches. I'm using a 15HP idler in my RPC and have a contactor rated at 125 amps as my main "on/off" contactor.

I have found ebay to be a great place to scrounge parts to build the RPC.

Rob

In a recent post a said that I didn't care for phase converters. I was speaking of the static type. I had forgot about the rotary kind. The static type is the only kind I have ever built.
I still prefer the VFD. I guess because I have been in the electronics field for so long. The prices are coming down and they are becoming more affordable for the average person. A 3 HP single phase VFD is selling for about $425.00 now.
My biggest complaint with the VFD is the line noise that they generate.
Let me know how your RPC turns out. I would be interested.

PS You can run multiple motors on a VFD. You just have to be sure and size it accordingly. I have a customer that is running 8 motors on one VFD.

IBM used to put RPC INSIDE some of their mainframes. It should be a 'quieter' power. The reason IBM did it was because they could never be 'sure' of the power that the customer would provide, and the RPC could handle lots of cleaning up of the electricity before it went to the internal power supplies. (This was on an IBM 4341 in the mid 1980's when I was around this)