# Phase convertors?



## TrxR (Mar 5, 2013)

I am looking at picking up an older Lathe and possibly a mill. Both of them would be 3phase but 3 phase is not available where I am at. Form what I have read the two best choices are RPC or VFD. With either of these options allow you to still use the factory speed controls or forward and reverse features of the machine? Ive also hear that the RPC put out dirty power is this something to be concerned about?  What are the pros and cons of each? 

Thanks


----------



## Tamper84 (Mar 5, 2013)

I am in the same boat. But I have decided to go with an RPC (mine is going to be hooked up and running on Friday  ). The reason being, you can run multiple machines off of one converter, also lets you use the machine as it left the factory. Which I like. Now with the output being "dirty" are you talking about the legs being unbalanced? Read up on phase balancing. What you do you balance the phases is add a capacitor in generated leg. http://www.hobby-machinist.com/showthread.php/12712-Rpc-simple-design-unbalanced Ulma Doctors right up is awesome!   Also in this thread, Ulma Doctor made two videos explaining it! http://www.hobby-machinist.com/showthread.php/12572-RPC-questions

HTH,
Chris


----------



## CluelessNewB (Mar 5, 2013)

Motor size is also an issue.  VFD's for motors over 3hp tend to be expensive making the RPC more attractive.  VFD's have the advantage of motor speed control.  With a VFD you probably will be able to use the original controls but they will need to be rewired.  Rather than "living electrically" between the motor and the input power they will get connected to the VFD low voltage control inputs.  The motor will be connected directly to the VHD with no switches between them.  The VFD will also provide overload protection so the old starter/overload will not be needed anymore.  I currently have 4 machines with VFDs my metal lathe, disc/belt sander, wood shaper and wood jointer.  In the long run it would probably have been cheaper to have built an RPC but having the variable speed has worked nice on the metal lathe and the wood shaper.  If you go with a VFD for the lathe look for one that is a "sensorless vector" drive, it will give you better results at low speed.


----------



## TrxR (Mar 5, 2013)

Thanks for the links and info. It kind of sounds like if you want to use the machine as it came from the factory the Balanced RPC is the way to go as well as the fact that one RPC will run both machines. The down fall would be noise, but if it was in another room or a small outbuilding you wouldn't really notice it. Is there any good how to's on building a balanced RPC? 

Thanks


----------



## Ulma Doctor (Mar 5, 2013)

i can instruct you on building a balanced RPC, if you are interested.
for a lathe or a mill, it's not super critical to have a balanced RPC.
the power isn't dirty, the third leg you are generating is just lower in voltage.
we balance the power by adding run capacitors between power legs.
more sensitive equipment that would be dependent on equal phases would be better suited for a VFD, as we can control different aspects of the circuit precisely.
shoot me a msg, i'll be glad to help out!)


----------



## Ulma Doctor (Mar 5, 2013)

TrxR said:


> Thanks for the links and info. It kind of sounds like if you want to use the machine as it came from the factory the Balanced RPC is the way to go as well as the fact that one RPC will run both machines. The down fall would be noise, but if it was in another room or a small outbuilding you wouldn't really notice it. Is there any good how to's on building a balanced RPC?
> 
> Thanks


the noise is not as bad as you might think, especially when a load is applied to the circuit.
when you are running the lathe/ mill etc. you may not even hear it.


----------



## Tamper84 (Mar 5, 2013)

From what I have read on the balancing issue is that it depends on what your output is from the converter. I am no expert. But, two of the legs should be close, but the generated leg is "usually" lower then the native. I have talked with a local guy that has been running his shop off of an old pull start rpc for years. No capicators or anything. Just straight from the rpc to the machines. But idk what affect it has on the motors. Anyway I have an understanding that you really can't balance the 3 legs until your up and running and figure out what capicators you need. 

HTH,
Chris

Well Mike, we were typing at the same time lol.


----------



## Rbeckett (Mar 5, 2013)

Mikes treatise on multi phase power is excelent.  His explanayion helped me understand the concept much better, it is definayely a must read for anybody considering VFD Vs RPC.  Thank for the info UD.

Bob


----------



## randyjaco (Mar 5, 2013)

I have both VFD and RPC. They both do well, but for what you say you want the RPC is the way to go.

Randy


----------



## alabamaed36046 (Mar 7, 2013)

I have been running a unbalanced rotophase since 1980. Its built from a 10 hp 3 phase using a 1/2 hp single phase to start.  Used to run lathes, mills and tool and cutter grinders.
No problems other than replace the start motor once.
Usually draws 16 18 amps at idle and 22 when running machines.
Power company inspected my setup and said I had better power factor than they had down on the road.

Easy to setup. Just be sure the low lead is not feeding the start relay coil. If converting 440 to 2230 be sure to get new trip heaters for the mag starters. The 440 heaters will trip on 220 due to increased amperage.
Hope this helps.
alabamaed36046

In south a Alabama


----------



## pecanguy (Mar 12, 2013)

I have a small autostart homebuilt RPC (2 hp) on my 1 hp Index mill.  It works very well.  I am not an electrician but, I worked in the electrical supply industry for a number of years.  Selling the parts and pieces, I am familiar with the uses of the various wiring and controls.  Most of my RPC information was gathered from various forums which was most helpful.  It is easy to balance the load lines with capacitors by trial of various sizes of capacitors.  You have to balance with the load running because it changes at idle (no load).  With a note on noise - once started you don't pay any attention to it, especially after you start the load.  Larger hp may be a little louder than my 2 hp.  My neighbor has a 6 hp.  You can build a balanced RPC for $100 (more or less) depending on the sources of your parts.  All of my components came from a local scrap metal yard (cheap).  Motors, relays, contactors, fuses & fuse blocks, capacitors, enclosure boxes, wire, indicator lights, switches & other misc.  You can do it!  It works!


----------



## joconnor (Mar 15, 2013)

Hi. I'm only 40 minutes from you. I run 2-mills, a lathe and a 1 ton overhead hoist on a homemade 5 HP RPC. Drop in and have a look if you wish. E-Mail, joconnor@nb.aibn.com.


----------

