To VFD or Rotary Phase converter

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Blind Squirrel

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I've been running my Bridgeport mill with a VFD for years and never a problem. I recently acquired a larger lathe to replace my bench lathe. This is also 220v 3 phase machine like the Bridgeport but a little larger motor. Also operates on 220v 3 phase. I could go with another larger VFD for the lathe or just switch everything over to a rotary phase converter set up. Any experience out there to help me lean one way over the other?

If I go VFD I have to go larger anyway or it will push the operating limits of the one I have. The one I have is only rated to 2hp which the mill is (but never pushed that hard). Also, it's a one person operation and only one machine is in use at a time.
 
I've never used the rotary phase converter setup, so I can't comment on that. I put a VFD on the mill I bought a few years ago and it's worked beautifully. They've become very inexpensive and just seems like the easiest way to go.

If I'm understanding right, you're considering paralleling both motors off one drive? Technically that's okay (think some sort of machine tool that runs two identical motors for some operation, where they always run together and at the same speed) but in your case you'll have to install a disconnect between the drive and each motor, and then remember to jockey them on and off depending on which tool you want to run. I guess if you accidentally leave one on and try to start the other tool the drive would detect the overload condition and fault out. Still it's kind of a hokey setup.
As cheap as they are now, why not just buy a second VFD for your lathe? I went with KB Electronics for my mill. They have a 240V single phase input at 2HP for $238

KBDF-27D - KB Electronics - AC Drives | Galco Industrial Electronics

I put mine in a small enclosure and added a pilot light so I'd know if I had the power on:
20190808_163128.jpg


drive box.PNG
 
I deal with VFDs as part of my job. Yaskawa has a nice converter/VFD combination that may be a solution for you. If you don't need the variable speed of a VFD a straight phase converter would be the better choice.
 
Why "switch both?"

VFD's can be expensive, you can find used rotary converters the same way you find used machinery. Run one off the VFD the other off a rotary
 
So I should further explain. At least some of what I understand. The mill is a manual mill and the VFD really only controls the motor. With the lathe. There are several electronic controls and the coolant pump (also 3 phase) to operate. Which if I infer from the information I've read. Leads to the best choice as being the RPC. But I'm unsure.
 
They make RPC's and they make static phase converters as well. You should have no trouble finding the best fit for your needs. You will have to size it for the total load of all the motors on you lathe.
 
Thanks for adding the extra info. Basically what the Variable Frequency Drives are designed to do is run a 3 phase motor of pre-determined size at either a fixed or variable speed. Because they use output transistors to create a synthetic 3 phase power, they can also provide a 3-phase output when powered by single phase input power. That's the upside to them, the downside is that those transistors don't like being energized with no load. In other words, they're NOT like a transformer, where you can have power applied to the primary (input) side and anywhere from full load to absolutely nothing applied to the secondary (output) side.

So with the additional components that need to be powered, a VFD probably isn't the easiest solution. I'm guessing the lathe's electronic controls will be coming off a transformer which will only need 2 legs of the 3-phase, so that you would wire to the power you're feeding the VFD with and not the output from it. The coolant pump is the tricky part. It will be cycling on and off and will provide an additional load to the drive. It was also designed to work best at 60Hz, which defeats one of the advantages of the VFD, being able to change the frequency and thereby the speed of the motor.

So the rotary phase convert is likely the best solution in this case. From what I know about them, they're more expensive but they provide the flexibility of powering all your equipment from one source.
 
There is a definite increased price for a 3 phase unit V.S. single phase however a small Allen Bradley Powerflex 4 or an ABB drive wont break the bank. I work in a Aviation plant so I install and work on these daily. As stated above you need to look at other items being fed from the source such as the pump.
 
I’ve built two rotary converters, a 5hp in garage for the mill and 3 hp in basement for EMCO lathe . I have a total of maybe $100 in both including the motors, relays for starting, and balance/run caps. The lathe had a two speed motor and it wouldn’t work well with a vfd. Vfd is great for speed control but one rotary can run a whole shop.
 
Looks like I'll be buying/building a Rotary converter. I completely forgot about the two speed motor. It wasn't the direction I really wanted to go. I have the VFD on the mill and it has worked flawlessly. I would have liked using one on the lathe also but it just doesn't seem to be the best choice. Well, I like new adventures. Thank you everyone for the inputs. Off we go!!!
 
You might be able to use the two-speed with a VFD by wiring in only the high speed winding. The way mine is wired to the multi-function switch, that wouldn't have worked too well. If you have any questions on the RPC, let me know. You can go simple with a rope pull start, or a little more complex with push button start and load balance caps.
 
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