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I was asked last week by a machine shop owner to help him out with a machine he had purchased for home use. It is a cnc machine from china that requires 380 volt 3 phase. He wants to use it in his garage and has 240 single phase available. He has found some options which are pretty expensive and I told him I'd do some research. I have used vfds to power 3phase from single phase but this machine has a main drive spindle fed from a vfd as well as 3 other motors for x-y and z axis which I believe are fed from a control transformer also electronics for the computer interface. Have not been able to find any such situation on the web. Hope someone can help. My guess is he's looking at spending another chunk of money. Thanks
 

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Bilge Rat
motors and controls.........
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This will be a bit more difficult than it seems; neither a phase converter nor a VFD will increase voltage. A transformer will be involved here.

If it were me, I'd get a transformer with a 240 3ø ∆ winding, and either a 380 ∆ or a 220/380 Y winding, and connect a rotary phase converter to the 240 side.

I wouldn't use Y to Y in this case, it'd tend to magnify voltage imbalance where a ∆ tends to balance voltage.
 

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I was asked last week by a machine shop owner to help him out with a machine he had purchased for home use. It is a cnc machine from china that requires 380 volt 3 phase. He wants to use it in his garage and has 240 single phase available. He has found some options which are pretty expensive and I told him I'd do some research. I have used vfds to power 3phase from single phase but this machine has a main drive spindle fed from a vfd as well as 3 other motors for x-y and z axis which I believe are fed from a control transformer also electronics for the computer interface. Have not been able to find any such situation on the web. Hope someone can help. My guess is he's looking at spending another chunk of money. Thanks
unless you have a motor generator converter or a really expensive inverter it wont work.

Whats the kva of the machine?
 

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You cannot run a VFD from a VFD, and if the other motors have transformers in front of them, that indicates this has a somewhat complex electrical control system inside with regard to how power is used and distributed. So anything you do, short of stripping the electrical out of it and rebuilding it, is going to involve making compromises and choices, many of which will involve the life of the equipment or the cost of running it. If you want NO effect on the like of the equipment, your only option is a Motor-Generator set, a system that will take in 230V 1 phase to be converted to run an AC induction generator, one that can be adjusted to 50Hz. If you just use what you have (because the line to neutral voltage is 220V on a 380V system anyway), then your frequency is wrong. On the VFD powered unit it won't matter, but it might on everything else.

Bottom line, this is a complex issue that needs careful investigation and discussion with your customer.

His bargain Chinese machine isn't such a bargain after all is it?
 

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Bilge Rat
motors and controls.........
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A motor-generator is different than a phase converter.

A phase converter simply manufactures a basic high leg, similar to a ∆, by using the existing windings of a 3ø motor. It cannot change frequency, and the line-to-line voltages are not very well balanced.

A motor-generator consists of a basic electric motor that is coupled to a basic electric generator. By varying the speed of the generator, the frequency can be changed. Also, the generator will produce balanced voltages.

This is the best way to go, but it is very likely the most expensive as well.
 

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If it was cheap, everyone would be doing it.
 

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You cannot run a VFD from a VFD, and if the other motors have transformers in front of them, that indicates this has a somewhat complex electrical control system inside with regard to how power is used and distributed. So anything you do, short of stripping the electrical out of it and rebuilding it, is going to involve making compromises and choices, many of which will involve the life of the equipment or the cost of running it. If you want NO effect on the like of the equipment, your only option is a Motor-Generator set, a system that will take in 230V 1 phase to be converted to run an AC induction generator, one that can be adjusted to 50Hz. If you just use what you have (because the line to neutral voltage is 220V on a 380V system anyway), then your frequency is wrong. On the VFD powered unit it won't matter, but it might on everything else.

Bottom line, this is a complex issue that needs careful investigation and discussion with your customer.

His bargain Chinese machine isn't such a bargain after all is it?
Not saying your wrong, but Im curious of the reasoning behind it.
 

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This will be a bit more difficult than it seems; neither a phase converter nor a VFD will increase voltage. A transformer will be involved here.

If it were me, I'd get a transformer with a 240 3ø ∆ winding, and either a 380 ∆ or a 220/380 Y winding, and connect a rotary phase converter to the 240 side.

I wouldn't use Y to Y in this case, it'd tend to magnify voltage imbalance where a ∆ tends to balance voltage.
While expensive we have installed motor generators that change and step up the voltage. of course his will be a custom installation that that will be pricey.
 

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Not saying your wrong, but Im curious of the reasoning behind it.
The output of a VFD is not really AC, it is DC, that an INDUCTION MOTOR will think is AC. But the input of a VFD, i.e. VFD #2 in the string, is not an inductive load, it has a diode bridge rectifier. The diodes conduct on what is called their Forward Conduction Voltage as the sine wave increases, and stop conducting when the sine wave crosses that point again on the way down. However there is no real sine wave on VFD#1 output. So the diodes on VFD#2 will see an instantaneous change in voltage instead of a gradual one, they turn on immediately, and conduct only as long as the VFD#1 pulses are close enough together to not allow it to stop. But that turns out to be a fraction of the sine wave time they expect, so they turn off then turn on again, etc. etc. The diode will pulse on and off multiple times in every cycle, and each time it does, there are essentially "switching losses" in it, meaning heat. The diodes then, not accustomed to high switching losses, heat up and short, which puts full AC on the DC bus of the drive and takes out the transistors. Game over.

Takes about 10 minutes. Don't ask me how I know... :eek:
 

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Head Grunt
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I would tell him to return it for a unit that he can actually work with without spending thousands of dollars to modify his own service feed. Sounds to me he stepped over a dollar to pick up a dime, now it is going to cost him.
 
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