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380 3 phase from 240 single phase

3K views 14 replies 11 participants last post by  just the cowboy 
#1 ·
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
 
#3 ·
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.
 
#6 ·
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?
 
#10 ·
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.
 
#8 ·
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.
 
#13 ·
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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