VFD selection for Tree 325 Journeyman - before or after RPC?

[specfab]

I have posted previously regarding my Tree 325J machine, and the 10HP shop RPC I use which appears to have a fairly high voltage (~265VAC) on its generated leg. I am returning to this project to try to get power squared away within the tolerances specified for the machine. I have not tried to tune the RPC up to now, as this seems like more room for unknown issues to crop up (from my viewpoint). I do have a couple of questions about possibilities for VFD power to this machine, though:

1. Based on what I see in searching on the topic here, 5HP is about the limit for single-phase inputs for commonly available VFDs. Please correct me if that is not the situation, and any recommendations for specific units of this type would be welcome. The Tree machine motor has a 5HP max output (15 min limit), so I am not too concerned about using a 5HP VFD at its limits very often. My assumption regarding "single-phase" is that this is a VFD powered by (2) hot legs of residential power at 240VAC between legs. Technically this is probably called split-phase(?)
2. If I were to power a 3-phase input VFD from the RPC, with its 242/265/242 voltage output, would this be "fixable" in the output of the VFD, i.e. to be able to get more similar voltage distribution between the 3 legs of VFD output?
3, Any recommendations for a source for high-quality caps for replacement in my RPC if I decide to break down and try to fix the actual source of the problem?

 

[motion guru]

Are you still running the original CNC control and spindle motor on that 325?

 

[Overland]

You can run most VFD's from single phase, with a reduced output. I run a 20 hp Fuji for my lathe off single phase, 220 volts.

 

[specfab]

Are you still running the original CNC control and spindle motor on that 325?

Yes, and I assume this presents another sort of problem, based on how typical VFDs like to be employed with direct (and unswitched) connection to the load.

 

[mksj]

VFD is not a 3 phase power source for a machine, it is designed to be a 3 phase power source for motors.
1. VFD's beyond 5 Hp are typically 3 phase input but most can be derated to run on single phase. The typical derating use to be a factor ~1.7 which no longer applies, you need to refer to the manufacturer's derating for the specific model.
2. A VFD output is independent of the input other than most cannot increase the output voltage above the line voltage unless there is some form of voltage doubler. That being said, adding the VFD to control the wild leg of an RPC is not a good use of the VFD. You would be much better off using a Phase Perfect 5Hp converter and getting rid of the RPC. The phase perfect will give you regulated and symmetrical 3 phase output.
3. You do not want the RPC wild leg to be connected to the transformer or electronics.

PTS005 - 5HP 230V Digital Phase Converter - Phase Perfect® Simple

www.phaseperfect.com

 

[Metalurgent]

I had a similar issue with high-leg delta power to my Journeyman 250. The original Yaskawa vfd worked fine with the high leg. It was important to make sure that the other two phases were the ones operating all the control systems; all power to the control transformers and to the servo power supplies and drives were from the low voltage legs. The only motors on my machine needing the extra leg were the lube pump and the spindle. The lube pump didn't seem to have any problem with the high-leg supply and the other 3-phase equipment in the shop ran fine , I just had to check that the control circuit voltages in the contactors were correct.
I've moved recently and I'll be facing a similar issue to you. All power to the three-phase machines in the shop will be from a home-made 15hp converter. My guess is that so long as I maintain a "spread" similar to the one that I had on the Farmer 3-phase, it will run fine.
When I set up the Hardinge CHNC retrofit with a Baldor VFD, I put three small line reactors before the VFD, and only because I had them sitting around. I don't think they really made a difference. Again, I just made sure that all the fancy stuff was connected to the low legs. I decided that all the machines had to have a consistent wiring procedure with the high leg always being the middle contact in a plug or receptacle and always a red wire.

In passing, I'm wondering if there is any specific difference between the the quality of power from a balanced converter vs. a high leg supply from the pole..?

 

[Almost Retired]

a properly tuned converter will be very close to utility supplied power
it is after all derived from the two legs of supply
the difference will come when it gets an increase or decrease in load
utility says bring it
rpc says oops time-out got to adjust the caps again

the crux of the matter being that caps need to be adjusted to suit the most common load motor/s amp draw

 

[specfab]

Thanks for the comments, all. I decided to build a voltage-monitoring display so I can see what is actually happening under load while the machine is running, before I go down a different rabbit hole. I found some inexpensive 0-300VAC voltmeter modules with digital display, and I'm planning to employ those in a permanent instrument for use either mounted to any machine, or to the RPC output as general indication of shop supply. The big challenge will be getting the wiring design correct so nothing blows up;-)

 

[motion guru]

I have replaced a number of Journeyman 425 Tree spindle drives using Nidec - Control-Techniques drives. The encoder on the Yaskawa motor is compatible with the standard encoder port on the drive and they have delivered solid performance with the original CNC control. Micheal Moore on this site also did this drive upgrade along with a centroid retrofit and he was happy with the results.

The Tree 325 has landed

Another delivery by Bob and his ever so handy crane truck. When I planned to put it into the same corner the old manual mill came out of, I didn't realize that the axis drive cabinet was going to prevent the collet closer from being inserted into the Mori Seiki spindle. Much prying and...

www.practicalmachinist.com

 

[red zilla]

a properly tuned converter will be very close to utility supplied power
it is after all derived from the two legs of supply
the difference will come when it gets an increase or decrease in load
utility says bring it
rpc says oops time-out got to adjust the caps again

the crux of the matter being that caps need to be adjusted to suit the most common load motor/s amp draw

So in theory a person could use an ardiuno with a Amp meter shield and some relays/motor starters connected to caps and write a code into the ardiuno to monitor the wild leg Amps and have it actuate the relay/motor starters to bring the caps in at different loads? If not an ardiuno some sort of PLC that can monitor line voltage and amps?

 

[SomeoneSomewhere]

So in theory a person could use an ardiuno with a Amp meter shield and some relays/motor starters connected to caps and write a code into the ardiuno to monitor the wild leg Amps and have it actuate the relay/motor starters to bring the caps in at different loads? If not an ardiuno some sort of PLC that can monitor line voltage and amps?

Sure; that's pretty close to the 'voltage support' role that capacitors and synchronous condensers have in utility networks. Certainly simpler than implementing power-factor correction, which plenty of large facilities have.

I wonder if anyone has tried building an RPC with a synchronous motor/generator instead of an induction motor? I *think* you should be able to use the excitation to adjust the output voltage on the generated leg, and over-/under-exciting it while connected to the grid causes it to generate/consume VARs.