Building and setting up a balanced RPC

[higgo]

SO....
The business I used to work for went broke and I bought one of their old machines.
I've moved the new machine (HITACHI SEIKI H20SII) into my shed at home and I've got to build a phase converter to run it. After speaking to a few people i'm on the right track parts-wise but i'm a bit unsure on a couple of setup issues...
1. Should I isolate the single phase controller transformer (220V to 100V) and run the controller separately from a different supply or just make sure that its not run from the wild leg? I've been told to do this by one company and they used to build RPC's. I reason that it mightn't work because the controller may have dramas if the drives "aren't there" when the it's powered up or vice versa?
2. I see no voltage marked for the 'V' phase on the machine and it seems to run none of the single phase side of things while U and W have voltages marked on the input transformer (480, 380, 240) and also voltages marked inside the control cabinet... so should i make V the wild leg?
3. I've read that some CNC drives convert AC to DC so that balanced phases aren't even as critical as RPC manufacturers make them out to be. I have Yakasawa drives on my machine... do they need balanced voltages?

I've got an Eurotech digital controller for the RPC that switches in banks of capacitors according to load. Hopefully when its up and running it should match the varying loads well. They use these in commercial CNC Phase Converters built here in Australia and i came across an older version as a kit.

I'd appreciate any help with these questions, no doubt a few others have similar ones however i've read and heard so many conflicting opinions on this topic that it would be great if someone who has 'been there, done that' could answer them.

[skullworks]

I have a 3hp CNC mill and it required a 10hp rated RPC with a 60Amp breaker to handle all the surge load requirements.

When the mill does tapping that RPC is fully loaded.

Like you I am investigating the option of powering the control directly from single phase.

[TRASHVOID]

I have used several Rotary Phase Converters; ranging from simple to complex.
When a machine is hooked up to the converter, the transformer(s) & control circuit(s) should be connected to the leads that are the main power feeds.
That would be lines 1&2 (L1, L2), the two ‘hots’, etc.
Avoid using the ‘ghost’ leg.
Use the transformer(s) taps that best match the voltage of your power source.
It can be tricky getting several machines connected correctly with proper motor rotation.
As far as connecting separate feeds to the same machine, it seems unnecessary & possibly a source of problems.
higgo, it looks like you need to connect to the U&W circuits…
Is that Hitachi Seiki a 15hp. lathe?
If so, that will pull a lot of juice running at full capacity.
And, as you probably know, you will need at least the same size motor for the converter as your machine has.

Chris

[Al_The_Man]

It should not be difficult to trace the 1 phase fed part of the machine to discover which 3ph pair feed it , this usually feeds the controller and possibly the servo's in some cases.
If you have the schematics, it should be easy to discover.
You should not need an isolation transformer, just trace the 3 phase pair that originates from the 240v 1 phase supply.
Al.

[higgo]

Thanks for the quick responses everyone. I think that running the controller from the converter is going to be the easiest way to do it, may be more trouble than its worth to isolate the controller input and feed it separately. Planning on running 480V split phase through the converter... this will output 480V three phase which I can then run though my machines input transformer to get 200V three phase. I know a retired electrical engineer so after i've got the converter finished he's going to drop by with his meters, help me hook it up and then check all the voltages under load. The converter is based on an 18.5kw 6 pole motor and eurotech digital controller. I'll post a few figures, hints and pictures on here when its done. Hopefully this will help as there seems to be a few people doing the same thing as me, that are not quite sure of which way to proceed.

[higgo]

Righto... got the controller the other day and it looks the goods! if it does what its supposed to i'll be happy but we'll have to wait and see. Seems that I have to put another transformer in front of the converter to drop the volts from 480V to 415V... bit annoyed because i wanted to use 480V through the whole lot and then drop it with the machine transformer to 200V or 220V. The controller manufacturers told me 480V was a no-no... might have a talk to my retired elec. engineer and see what he thinks. Anyone got any ideas about a cheap transformer to do this? I've got a few quotes and although they're not too bad at around $900 if i can find a source for a cheaper one i'll use it. Maybe some old machines use one? Think i might go to the surplus store and have a look.