VFD or rotary phase converter

I am getting a lathe and it is 3 phase. I was told if I get a VFD, I can adjust the speed of the lathe from 0 to max speed, and they are a little cheaper the lathe is 16 speed 45 rpm to 1800 rpm. If I get a rotary phase converter and get it big enough I could add more 3 phase equipment. The lathe is 3hp so if I bought a 9 hp converter that would allow room for expansion. What would you recommend?

Thanks for your help,
Randy

Rotaries suck.. They tend to be loud and they eat a TON of electricity..

And then you have to go and turn it on... Turn it off... Turn it on... Turn it off.

With a VFD its a button right there at the lathe, its not loud, its not an energy hog,
and you get to vary your rpms without switching gears.

Hands down VFD. I suggest Automation Direct. Good and actually helpful sales. Good return policy. Good actually readable printed hardbound manual. Reasonable price. I have three.

Denis

Primitive56 said:

I am getting a lathe and it is 3 phase. I was told if I get a VFD, I can adjust the speed of the lathe from 0 to max speed, and they are a little cheaper the lathe is 16 speed 45 rpm to 1800 rpm. If I get a rotary phase converter and get it big enough I could add more 3 phase equipment. The lathe is 3hp so if I bought a 9 hp converter that would allow room for expansion. What would you recommend?

Thanks for your help,
Randy

Click to expand...

Pro: For the RPC is that is can operate ALL 3-P on the lathe with one source. Coolant pump, lights, etc. and yes - "many" other machines, instead-of, or sometimes at the same time.

Con: As noted already, plus limited to roughly 90% of load-motor nameplate power, best-case.

Pro: For a VFD is inherent soft-start, variable speed, low wasted energy, heat, or noise.

Con: Is they aren't comfortable with more than a single load motor per-each VFD, and are not always easy to integrate if one wants to retain OEM controls, rather than what the VFD furnishes.

Monarchist said:

Pro: For the RPC is that is can operate ALL 3-P on the lathe with one source. Coolant pump, lights, etc. and yes - "many" other machines, instead-of, or sometimes at the same time.

Con: As noted already, plus limited to roughly 90% of load-motor nameplate power, best-case.

Pro: For a VFD is inherent soft-start, variable speed, low wasted energy, heat, or noise.

Con: Is they aren't comfortable with more than a single load motor per-each VFD, and are not always easy to integrate if one wants to retain OEM controls, rather than what the VFD furnishes.

Click to expand...

I opted for the rotary phase converter (currently on a static converter) for my 2 hp Sheldon lathe. As mentioned when going to the VFD in this case none of the original controls could be used. This particular machine uses a gear motor and Worthington drive for speed changes. With the VFD all parameters would have to be programed into the VFD. I wanted to keep the original control console (Start, Stop, Forward, Reverse, Fast & slow) so a VFD wasn't the answer.

I have the same situation on a Bridgeport mill with the J2J variable speed head. Since I wanted to use the original controls a VFD wasn't the answer. I'm sure there are situations where the VFD would be preferable to a rotary phase converter. You just have to decide what functions you want to control with the original machine controls and which would be better controlled through the VFD.

Here's an older picture of the Sheldon control Station. There's now also a tachometer in the headstock cover that's open in the picture. I wanted to use these conveniently located controls rather than have to mount a VFD in a position where it would be not only convenient, but in a place where it wouldn't get covered in cutting oil and swarf.

Primitive56 said:

I am getting a lathe and it is 3 phase. I was told if I get a VFD, I can adjust the speed of the lathe from 0 to max speed, and they are a little cheaper the lathe is 16 speed 45 rpm to 1800 rpm. If I get a rotary phase converter and get it big enough I could add more 3 phase equipment. The lathe is 3hp so if I bought a 9 hp converter that would allow room for expansion. What would you recommend?

Thanks for your help,
Randy

Click to expand...

A VFD is not a general power source. You mate it with a motor and set up its parameters and it stays that way, unless you really like changing umpteen parameters every time you want to run a different size motor on it.

Primitive56 said:

I am getting a lathe and it is 3 phase. I was told if I get a VFD, I can adjust the speed of the lathe from 0 to max speed, and they are a little cheaper the lathe is 16 speed 45 rpm to 1800 rpm. If I get a rotary phase converter and get it big enough I could add more 3 phase equipment. The lathe is 3hp so if I bought a 9 hp converter that would allow room for expansion. What would you recommend?

Thanks for your help,
Randy

Click to expand...

Standard induction motors don't like running 0 rpm for very long with any kind of load. Most basic VFDs will let you go down to about 40% speed without problems, more advanced ones might do better. A lot depends on the motor and it's winding insulation as well as how it is cooled. VFD rated motors are obviously the best for that application but most lathes came with standard motors for across the line starting/running.

VFD no question. It will give you variable speed and power brakes. Most machine tools the original controls can be used. The Bridgeport no problem at all. Just needs some rewiring of the switches.
On a VFD no switches between the VFD and motor. All switching is low voltage.
That lathe setup I see why no vfd. It sounds like a weird setup of a motor controlled revves drive adjustment.
Bill D.

Bobw said:

Rotaries suck.. They tend to be loud and they eat a TON of electricity..

And then you have to go and turn it on... Turn it off... Turn it on... Turn it off.

With a VFD its a button right there at the lathe, its not loud, its not an energy hog,
and you get to vary your rpms without switching gears.

Click to expand...

In fact, they do not draw much extra power, that just is not a big deal. They also do not have to be loud.

But a VFD does so much more, that it can be a lot nicer to have.

Plainly put, if you need or envision running more than one motor, you want a converter. If you just need to run one motor on one machine, VFD is a good idea. As said, you don't get 0-whatever rpm, the motor will overheat at very low speeds and you'll have no power. That's another huge advantage to using the geared speed changes on the machine, torque multiplication.

Most likely, if you use a VFD on your lathe you will run it 95% of the time in a single mid-range to upper range gear but tune the RPMs using VFD adjustment. For heavier cuts you will switch into back gear but not necessarily change your selected running gear. Occasionally you will change your running gear for more unusual power/RPM combinations. If you go with the RPC, you will change gears all the time. No big deal, but mighty nice to be able to tune your RPMs on the fly---especially on facing cuts. They usually don't require a lot of power, but nice to rev up as you cut.

Just throwing the arguments out there. My EE has on-the-fly RPM adjustment, so an RPC is fine for it. But on a fixed RPM motor, not so much.

Denis

Primitive56 said:

What would you recommend?

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You get one and you wish you had the other, and vice versa. Especially when the ONE unit breaks. Get both.

JST said:

In fact, they do not draw much extra power, that just is not a big deal. They also do not have to be loud.

But a VFD does so much more, that it can be a lot nicer to have.

Click to expand...

I think it was the 20hp I had was pulling 12 amps at idle.. And they are running even when your machine isn't.

Going from running rotaries to real 3 phase in the same building with the same machines the electric bill dropped
from an average of $800 a month to $400

Bobw said:

I think it was the 20hp I had was pulling 12 amps at idle.. And they are running even when your machine isn't.

Going from running rotaries to real 3 phase in the same building with the same machines the electric bill dropped
from an average of $800 a month to $400

Click to expand...

That is a common mistake. People see the 12A, multiply by 240, and freak out. In fact, it probably amounts to a whopping couple hundred watts or so, no more than 2 or 3 old fashioned light bulbs. Maybe 20 cents every 3 hours.

That 12A was at a very low power factor, and the "real power" is about 1/10 or so of what it appears to be.

Of course, a VFD can be 97% efficient, as is a Phase Perfect, but the contrast between them is not nearly as dramatic as it appears if you don't consider power factor.

Is a VFD complicated to hook up, or is there just a L1, L2 and ground for incoming 1 phase, and a place for the 3 leads on the motor and a ground or is it more complicated than that? Is it complicated to set the parameters on the VFD or are the factory parameters ok? Any brand better than others better customer service?

Thanks for all of your help,

Randy