rotary phase converter VS VFD

A

alinwa

oft dis'd member
My son just bought an old Charmilles D10 sinker EDM, a 3KW machine

He's in a residential area with no 3-Phase running to his shops. 120A service panels.

Guys on some forums are saying it "requires a rotary phase converter" while I'm suggesting a cheap VFD

Does anyone here know of situations where a VFD WILL NOT WORK to replace an old school phase converter?
 
al,
i ran a rotary and it worked fine
i have read that it really depends on load.
i never ran my lathe anywhere near full load, so it
THINK i could have done a vfd.
i am planning on a vfd when i reinstall my lathe.
 
alinwa said:
My son just bought an old Charmilles D10 sinker EDM, a 3KW machine

He's in a residential area with no 3-Phase running to his shops. 120A service panels.

Guys on some forums are saying it "requires a rotary phase converter" while I'm suggesting a cheap VFD

Does anyone here know of situations where a VFD WILL NOT WORK to replace an old school phase converter?
Click to expand...


At this point the VFDs have dropped in price enough to be less expensive than a RPC and a lot more efficient.
Even if you never use the Variable function it produces a 'cleaner' 3-phase voltage set than all but the largest rotaries
running a far smaller load.

What voltage is the sinker motor set up for?
You will need to use the numbers off the motor itslef to set up whatever solution you end up with.

Make sure the setup is large enough even if you never approach the actual motor rating in use.
The motor will start better (faster) and run smoother with a converter that is larger than the minimum required.

Article 430 covers motors.
430.122 covers the VFD feed requirements.

NEC sections 215.2(A)(1), 220.40, 220.50, 220.12(C), 430.24, and 409.20 may be useful.

Good luck.
Especially if you get things inspected.
Many residential code officials have very limited experience and training in industrial type equipment connection.

I have met more than a few that had no real knowledge of how Article 430 and motor feeds and breakers are sized and selected.

The normal rather strict pairing of breaker size and conductor size are NOT the same as for 'general use' branch circuits.
Plenty of them barely understand the correct installation of Hermetic Compressor feed (think residential central A/C).

Induction motors and their controller equipment are designed to prevent overloading of feeders and overheating of the motor.
The breakers are solely for short circuit protection of the feeder to the motor controller.
 
Last edited:
Vfd

Al, to answer your question, there is no problem using a VFD
that is correctly chosen to convert single phase 220 vac 60 hz to three phase 60 hz 220-440 vac.
I’m a little surprised to see that the house only has 120 Amp service.
If possible, talk to a sales person about help choosing the right converter for your application,
otherwise you will have to do a little math to make that choice.

Bob
 
Bob1949 said:
Al, to answer your question, there is no problem using a VFD
that is correctly chosen to convert single phase 220 vac 60 hz to three phase 60 hz 220-440 vac.
I’m a little surprised to see that the house only has 120 Amp service.
If possible, talk to a sales person about help choosing the right converter for your application,
otherwise you will have to do a little math to make that choice.

Bob
Click to expand...

Home and two outbuildings, the outbuildings are served by smaller panels
 
alinwa said:
Home and two outbuildings, the outbuildings are served by smaller panels
Click to expand...

Unless he's planning on moving to a different building, the first thing I'd do is bite the bullet and put in a 200A 220V feed to his outbuilding. As long as the main panel is not overloaded, just install another 200A breaker and feed the outbuilding from the main. All depending on the size of the main panel he has now. Saves on having 2 services, which can be a real can of worms.

In today's world and unless you have an anal inspector living next door, what's written on the drive is close enough. No need for any needless calculations.

Usually no one rigs up a EDM in an empty building. They breed and before you know it you have to move to bigger buildings.
 
alinwa said:
My son just bought an old Charmilles D10 sinker EDM, a 3KW machine

He's in a residential area with no 3-Phase running to his shops. 120A service panels.

Guys on some forums are saying it "requires a rotary phase converter" while I'm suggesting a cheap VFD

Does anyone here know of situations where a VFD WILL NOT WORK to replace an old school phase converter?
Click to expand...

About the only thing you cannot do is disconnect the load from the drive, which is in direct violation of the codes.
 
TRA said:
Unless he's planning on moving to a different building, the first thing I'd do is bite the bullet and put in a 200A 220V feed to his outbuilding. As long as the main panel is not overloaded, just install another 200A breaker and feed the outbuilding from the main. All depending on the size of the main panel he has now. Saves on having 2 services, which can be a real can of worms.

In today's world and unless you have an anal inspector living next door, what's written on the drive is close enough. No need for any needless calculations.

Usually no one rigs up a EDM in an empty building. They breed and before you know it you have to move to bigger buildings.
Click to expand...

Somehow I've been unclear..... the home is served by 200A and each outbuilding has a 120A 220V panel

The machine only draws 3A as I understand. I don't imagine draw being the issue
 
alinwa said:
My son just bought an old Charmilles D10 sinker EDM, a 3KW machine

He's in a residential area with no 3-Phase running to his shops. 120A service panels.

Guys on some forums are saying it "requires a rotary phase converter" while I'm suggesting a cheap VFD

Does anyone here know of situations where a VFD WILL NOT WORK to replace an old school phase converter?
Click to expand...

Al, the EDM does not know what produced the 3 ph power. Just make sure that the variable freqency drive (VFD) is set to the frequency that the EDM requires. Being old the EDM may not respond well to something else. Also, make sure that the VFD is capable of supplying the 3kw min and better to double that to 6 or 10... more the better.
 
A VFD should be cheap and work just fine. Just get one designed for single phase input. Some are 3 phase in a variable frequency out. A rotary phase converter can be built with a 3 phase motor and a few run capacitors. It is cheap, quick, and easy if you have an old 3 phase motor laying around.

Michael
 
TRA said:
As long as the main panel is not overloaded, just install another 200A breaker and feed the outbuilding from the main.
Click to expand...


There are many panels that are not rated to have a breaker larger than 100 amps installed on the buss.
Make sure you check the specs on the panel you are feeding from.

The breaker-to-buss contact points are often not all that large or 'heavy' enough.
 
mturner said:
A VFD should be cheap and work just fine. Just get one designed for single phase input. Some are 3 phase in a variable frequency out. A rotary phase converter can be built with a 3 phase motor and a few run capacitors. It is cheap, quick, and easy if you have an old 3 phase motor laying around.

Michael
Click to expand...

And then you need a way to START the 3-phase 'idler' motor.
It has to spin up to at least close to operating speed to be 'captured' by the feed.
The idler motor also has to be at least as large as the motor you are trying to supply.
Larger produces a voltage closer to being balanced on the generated phase.
 
brickeyee said:
And then you need a way to START the 3-phase 'idler' motor.
It has to spin up to at least close to operating speed to be 'captured' by the feed.
The idler motor also has to be at least as large as the motor you are trying to supply.
Larger produces a voltage closer to being balanced on the generated phase.
Click to expand...

I used my homemade rotary phase converters for many years. Just threw a lever an they fired right up. Never had a special way to get them up to speed, other than capacitors.

Michael
 
mturner said:
I used my homemade rotary phase converters for many years. Just threw a lever an they fired right up. Never had a special way to get them up to speed, other than capacitors.

Michael
Click to expand...

I've seen rotary's that were started with a pull rope. As long as you can spool it up enough to start, ya don't need any Capacitors. They just clutter things up. NOW, if you are real ambitious you can use capacitors and use them to start the rotary. But that's a lot of jacking around that is not necessary. I built mine with a 3ph knife switch, a 20hp 3ph motor. OH ya, use at least a 1750 rpm motor, and hook it shaft to shaft to a ~2hp 1ph to spool it up. The are just plain simple to build. Farmers have been using them for many decades. Use your ambition and integrate a 3ph panel into the system and when you need another machine to hook it up, just pop in another 3 pole breaker and wire an you are good to go.
 
TRA said:
I've seen rotary's that were started with a pull rope. As long as you can spool it up enough to start, ya don't need any Capacitors. They just clutter things up. NOW, if you are real ambitious you can use capacitors and use them to start the rotary. But that's a lot of jacking around that is not necessary. I built mine with a 3ph knife switch, a 20hp 3ph motor. OH ya, use at least a 1750 rpm motor, and hook it shaft to shaft to a ~2hp 1ph to spool it up. The are just plain simple to build. Farmers have been using them for many decades. Use your ambition and integrate a 3ph panel into the system and when you need another machine to hook it up, just pop in another 3 pole breaker and wire an you are good to go.
Click to expand...

I have put together dozens of these over the years.

The 'final' version I made the greatest number of used a small rubber wheel on the 1-phase with a simple lever to push it against a pulley on the 3-phase to spin it up before applying power to teh 3-phase.

You could then apply the output of the 'open' leg of the idler 3-phase together with the two 240 V legs to make a 0 degree and +/- 180 degree 'phases.'
That was 'close enough' to allow aa 3-phase to start up all by itself.

There have been multiple examples of this in Fine Woodworking Magazine over the years.

Some of the older monster size (think wheels over 30 inches) handsaws had 'integrated' 3-phase motors driving them.

I had an Oliver (36 inch) that was like this.
Before the technology existed to easily control 240 V AC to even make a VFD.

It was easier to run a large idler to create a 0 degree phase between the two 180 degree legs of single split phase.

Some early versions tried to use capacitors to drag the split phase legs over a few degrees but that takes a lot of largish high voltage non-polarized capacitors.
It turned out to not be required but it does produce a slight penalty in the 3-phase motors about power.

Not enough to matter in anything except real production operation with 'full' cuts being made.
 
Pete Wass said:
the new Griggly machines come three phase WITH a VFD, some of them, at least.

Pete
Click to expand...

The hardest part of designing with them is making sure they have adequate heat sink contact and the heat sink is
large enough with adequate air flow.

I had massive 3-phase AC electronic loads when working on this stuff.

They had there own 6 foot tall 19 inch rack with forced cooled air (we actually used a Unico high pressure A/C unit)
for that single rack of equipment.

And they still shut off on temperature occasionally with a 4-ton compressor on the roof.
Usually in the summer during the day.
We had to switch to testing well after dark, and even put additional fans on the roof for the compressor.
 
I'm going to go out on a limb here and risk exposing my ignorance.

A VFD is designed to power a motor. There are many 3 phase applications that don't involve a motor, where a VFD will not work.

You can use the VFD to drive the motors on the sinker, but you cannot use it to supply power to the control system. VFD's use a bunch of "tricks" to do their magic. Motors don't mind the tricks, but many other systems will have a problem with it. In other words, a VFD should not be used as a general 3 phase power supply. It's possible that if you left the VFD locked at 60hz, it might work, but it's still converting AC to DC and then using something similar to pulse width modulation to create the 3 phase supply. Most VFD's are "smart" these days, and it will probably figure out that it's not connected to a motor and might just throw alarms.

If you need a 3 phase power supply for the entire machine, a rotary phase converter is the way to go.
 
Last edited:
Great explanation

James Lederer said:
I'm going to go out on a limb here and risk exposing my ignorance.

A VFD is designed to power a motor. There are many 3 phase applications that don't involve a motor, where a VFD will not work.

You can use the VFD to drive the motors on the sinker, but you cannot use it to supply power to the control system. VFD's use a bunch of "tricks" to do their magic. Motors don't mind the tricks, but many other systems will have a problem with it. In other words, a VFD should not be used as a general 3 phase power supply. It's possible that if you left the VFD locked at 60hz, it might work, but it's still converting AC to DC and then using something similar to pulse width modulation to create the 3 phase supply. Most VFD's are "smart" these days, and it will probably figure out that it's not connected to a motor and might just throw alarms.

If you need a 3 phase power supply for the entire machine, a rotary phase converter is the way to go.
Click to expand...

Electronics and electrics have always been a black hole to me.

Thanks,

Pete
 
Whether using a Rotary or a VFD, the motor is the only load per drive. With new machines with VFD spindles the spindle is the only load on the drive. Controls used on most machinery are single phase. You should never connect the control power to the wild leg of a rotary or a FVD. If you are running a simple machine like a drill press, or a machine with no controls other that an on-off switch, either type makes little difference. When you graduate up to machinery with controls, things get complicated. We build machines that can have everything corm 480 3ph down to 5 vac all in the same panel. Each voltage is dealt with a different supply.
 
You must log in or register to reply here.
Back
Top