rotary phase converter VS VFD

[alinwa]

Are there any situations where a VFD WILL NOT take the place of an old school rotary phase converter?

My son is ready to wire an old Charmilles D10 plunge EDM into a residential circuit, getting conflicting opinions from forums, few explanations nor facts.

 

[jmm03]

alinwa, I don't know if you have been to this site,but I have found answers there and usually not alot of BS. https://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/
Some machines are affected by high frequency feedback from VFD's . I have heard they are not good on certain welding machine applications, but I have not personally used them like that. I have used them to power machine tools from single to three phase without issues. There can be low end torque issues at low speeds on some motors, but what can be problematic on an EDM machine I would not know, unless there might be interference between the VFD and the electronics of the EDM. Jim

 

[ebb]

The complex set up was a turn off for me. I know nothing about electronics and was afraid I couldn't figure out how to make it work.

 

[rcparker1]

Some newer vfds will allow you to use single pahse to run a 3 phase machine and still give you speed control a phase converter can not. Small vfds on 5hp or less have become very affordable too. I would highly recommend a vfd. I have put vfds on all my mills and lathes.

 

[alinwa]

OK..... I think I'm getting convinced

First of all, I know nothing about the whole "motor phase converter" thing because all I've done is wire one VFD to my olden days 1947 vintage Bridgeport which is written "440/480" on the side and 3-phase on the tab. It came out of a school shop. The guy I bought it from had several setups for sale, hunnerds of pounds and hunnerds of dollars worth of stuff and needed an electrician to wire it...

I ordered up a cheap VFD and a some mid-priced DRO's and set it all up myself and it's AWE-SOME!!! Just 'WAYYY cooler than the ones I ran yrs ago in school with the Trav-A-Dials and such...

I just maintain a butt-ignorance of things electrical so I have to ask

 

[alinwa]

On the VFD or phase converter?

Last VFD I installed was basically ready to go out of the box.

Seperate 3-phase motor? Drive belts and sheives


Essentially, a rotary phase converter was the best option before cheap electronics.

Now days, the tables have turned. As I said, I work on locomotives. 2500 amps and 1250 volts. VFDs can handle a load without costing the same as a lunar module.

Thank you someoldguy...... that's the answer that makes me happy.


Now if someone had said "NO! NO! NO! Yer gonna' put'cher eye out!!" and explained WHY, I'd reconsider sharing my thoughts with TwoSon..... but when you said "they runs trains with them"..... that's real-world, to me.

 

[hoz53]

OK..... I think I'm getting convinced

First of all, I know nothing about the whole "motor phase converter" thing because all I've done is wire one VFD to my olden days 1947 vintage Bridgeport which is written "440/480" on the side and 3-phase on the tab. It came out of a school shop. The guy I bought it from had several setups for sale, hunnerds of pounds and hunnerds of dollars worth of stuff and needed an electrician to wire it...

I ordered up a cheap VFD and a some mid-priced DRO's and set it all up myself and it's AWE-SOME!!! Just 'WAYYY cooler than the ones I ran yrs ago in school with the Trav-A-Dials and such...

I just maintain a butt-ignorance of things electrical so I have to ask

Not all VFDs are set up to use as phase converters. You have to make sure and check in the specs they are or specify that when you’re ordering. Of coarse the vfd also has to be ordered setup for the correct input and output voltages. Also different VFDs give you different characteristics. Like some give you constant torque throughout their operating range. Motors to be operated with VFDs should be “inverter rated”. The old motors aren’t and generally people just use them anyway until they fry. The first vfd I purchased was I think a Mitsubishi and I could not figure out the programming so never got it working. I’m gonna try a Teco next. I have heard of people having good luck with them. If all you’re operating is a 3 phase motor(s) on the old machine a vfd will work fine. If something else I don’t know.

 

[Dusty Stevens]

My rule for myself is anything bigger than a 7.5hp needs a rotary converter putting out a true 3ph. You can always get a 3ph to 3ph vfd to run your final motor. If its under 5hp you can run it on a 1ph to 3ph vfd just fine.

 

[TRA]

AL, for things like fans, motors and other simple loads a VFD works great. We use about a truck load of them per year. For loads like older mills or lathes they "suck" and you would be better off with a rotary. A small VFD works best being used as a static power supply. Unless they are integrated into a control panel, they are a pain in the ass to operate the machine tool they are powering. By now you could probably imagine how much of a drag it would be to run a good sized gear head lathe with just a VFD. I for one would not want to have to operate some of these older machines where when it's turned on the spindle is turning. All the while trying to dodge chips and reaching up over the machine to get at some button that belongs on a cell phone.

I'm no locomotive guru, thankfully, but keep in mind you cannot power down a machine while connected to a VFD. You will have to do that at the drive, as the drive will fault and need to be reset. Some are worse than others. We prefer Yaskawa. They are like a Timex.

VFD's are a God send for some things, but a total PIA, for others.

 

[alinwa]

AL, for things like fans, motors and other simple loads a VFD works great. We use about a truck load of them per year. For loads like older mills or lathes they "suck" and you would be better off with a rotary. A small VFD works best being used as a static power supply. Unless they are integrated into a control panel, they are a pain in the ass to operate the machine tool they are powering. By now you could probably imagine how much of a drag it would be to run a good sized gear head lathe with just a VFD. I for one would not want to have to operate some of these older machines where when it's turned on the spindle is turning. All the while trying to dodge chips and reaching up over the machine to get at some button that belongs on a cell phone.

I'm no locomotive guru, thankfully, but keep in mind you cannot power down a machine while connected to a VFD. You will have to do that at the drive, as the drive will fault and need to be reset. Some are worse than others. We prefer Yaskawa. They are like a Timex.

VFD's are a God send for some things, but a total PIA, for others.

OK...... while I get the whole "winding down" thing, my Bridgeport still turns on/off using the switch and while I can't brake it to an instant stop like I useta'could it still comes down a whole lot quicker than letting the VFD wind down.

I can see where on a large machine it would be like "go for coffee while it shuts off"

 

[Someoldguy]

Ok, I'm out.

Good morning to you fellas.

 

[TRA]

OK...... while I get the whole "winding down" thing, my Bridgeport still turns on/off using the switch and while I can't brake it to an instant stop like I useta'could it still comes down a whole lot quicker than letting the VFD wind down.

I can see where on a large machine it would be like "go for coffee while it shuts off"

You can brake with a VFD, but then you will need to install a breaking resistor, and program it to do so.

It's that the drive cannot tolerate the "inrush" caused by switching motors downstream from the drive. Large lathes almost all have a foot break to switch the current and stop the head stock. There a lot you can do, especially once you learn how to program them. But as always all those extra terminals in those drives are to, force the 5v card power, activate the on board IO, start, stop, vs. They even work better that you'd believe, in an indexing application. They can stop on a dime and be repeatable well,,about as good as a lot of low resolution machines.

Anyone considering playing with all the bells and whistles would be best advised to mount the Drive on a wall or whatever. Then round up a small HMI, and you got yourself a redneck CNC.

You will do just fine, but they can and most generally will fault due to switching under power. . Some will fault and will not restart..Toasted...That's when you are glad you bought a quality drive from a reputable dealer.

 

[JFrank]

I dont crank locomotives so who knows. Im an electrical engineer for ge. Id bet the engineer gets to crank them under agreement and if they dont crank they call you under an agreement. Ive never walked up to one not running to tell you the truth. And that pic is misleading- ive got a costanza cut

And a pony tail

 

[shortgrass]

An EDM machine of any size has a pretty heavy electrical draw. How many amps does this machine your son have, need? For me, that would be the deciding factor, amps required for proper operation....

 

[hoz53]

Are there any situations where a VFD WILL NOT take the place of an old school rotary phase converter?

My son is ready to wire an old Charmilles D10 plunge EDM into a residential circuit, getting conflicting opinions from forums, few explanations nor facts.

Sorry I should not have got involved in this

 

[alinwa]

An EDM machine of any size has a pretty heavy electrical draw. How many amps does this machine your son have, need? For me, that would be the deciding factor, amps required for proper operation....

It's a 3KVA machine

 

[alinwa]

You can brake with a VFD, but then you will need to install a breaking resistor, and program it to do so.

Thank you, I considered braking resistors for my mill but decided against it..... for the EDM it seems unnecessary.

 

[butchlambert]

Thank you, I considered braking resistors for my mill but decided against it..... for the EDM it seems unnecessary.

I have braking resistors on both of my old (1956) Bridgeports. You can program instant start and stop or slow ramp up and braking. I can turn the on-off-reverse switch to instantly reverse the motor. Ain't burnt up my antique motors yet.

 

[hpshooter]

I have braking resistors on both of my old (1956) Bridgeports. You can program instant start and stop or slow ramp up and braking. I can turn the on-off-reverse switch to instantly reverse the motor. Ain't burnt up my antique motors yet.

Nor have I. 80's vintage "Hung Chow" or other generic Asian motor on a Super Max mill. Fully accept the fact the smoke could leak out of the motor at any time but I have a full can of Genuine Factory Lucas replacement smoke I keep on hand for a couple Norton motorcycles and two Brit project cars.

 

[Gun Smith]

Seems to me that if the EDM machine has multiple motors, that one VFD would not work. Most likely it has at least two motors.
Then again, that's just a WAG. Go to Practical Machinist as linked above, as I believe there is an EDM forum there, as well as
a VFD forum. Also, CNC Zone - https://www.cnczone.com/forums/index.php has EDM info.