Digital phase converter build?

[robertl]

Hi all
I am looking at three phase conversion options for my workshop I have looked at rotary converters
and I have also looked at static and digital conversion options what I'm wondering is does anyone have a digital converter from the only manufacturer that makes them. Drives Direct is the name.
If so how well does it work and what is your experience with it?
I'm looking at getting 3 phase from the grid (extremely expensive) and also looking at getting a rotary converter with digital phase balance. from the USA.
The only other option I can come up with is to design and build a digital phase converter on my own, i have a lot of experience in electrics and electronics but cant figure out exactly how the digital phase converter works. The basis of it must be a VSD with Harmonic filter in front, and Sine Wave filter on the output side. And a bank of capacitors on the output to take the start current. But apart from that im not sure what else. And those bits alone in no way could justify the cost they charge. Seeing one would help or any ideas any of you may have.

 

[brianmoooore]

Son in law manufactures 5 axis CNC machines, and buys in single to three phase digital convertors from China all the time. Not particularly expensive, as far as I know.
Another way you could manage is to set up a three phase motor running on single phase with a capacitor (Steinmetz circuit), then once this is running, powering nothing, you can take power from its three terminals to feed another motor of equal or less power. If you have these two motors running, you can then run a third with a power equal to the sum of the first two, and so on.

 

[robertl]

Son in law manufactures 5 axis CNC machines, and buys in single to three phase digital convertors from China all the time. Not particularly expensive, as far as I know.
Another way you could manage is to set up a three phase motor running on single phase with a capacitor (Steinmetz circuit), then once this is running, powering nothing, you can take power from its three terminals to feed another motor of equal or less power. If you have these two motors running, you can then run a third with a power equal to the sum of the first two, and so on.

Ive looked at the inverter options as you mention, also the 2nd option you mention is basically a simple rotary converter, but wouldnt be great for cnc stuff, digital seems the only real option.

 

[brianmoooore]

A true rotary convertor is a single phase motor directly driving a three phase generator. I had a customer with a 6kW sewage pump that had been supplied for single phase use with a control box containing a Steinmetz circuit. This proved unsatisfactory because of the reduced power and starting torque of the pump, so I eventually fitted a genuine rotary convertor which restored reliability.
The arrangement I described above is a bit of a hybrid between Steinmetz and a rotary convertor.
Steinmetz circuits can be effective. I have a hydraulic four post car lift in my garage with a 2kW 3 phase motor, which I've had happily working on single phase for about 15 years or so. The lift has mechanical latches every few inches of lift, so the motor actually starts under zero load until the pump develops pressure.
The CNC machines run 2kW motors, IIRC, and the convertors are appreciably less than £100 a pop, I think.

 

[Lucien Nunes]

A true rotary convertor is a single phase motor directly driving a three phase generator

Strictly speaking we should call that a motor-generator. A rotary converter is only one machine, with multiple windings if required, but a motor-generator is two.

design and build a digital phase converter on my own

That is hard work. My background is power electronics and I wouldn't bother attempting it for a one-off. Sure, you can buy an all-in-one bootstrap driver IC and six IGBTs and a few dozen other components, drive it from a micro and presto, get a 6-pulse output. But will it cross-fire and self-destruct when you switch the load off? Will it commutate reliably at low PF? I could go on for hours with what-ifs, but the designers of the commercial product did all of that already and to a large extent that is what you are paying for, not the parts.

 

[brianmoooore]

, but the designers of the commercial product did all of that already and to a large extent that is what you are paying for, not the parts.

Leave it to the Chinese. It's what they're good at.