3 Phase Convertors

[HAWK]

TIME TO BUILD:

I have found several schematics for constructing 3 phase convertors. I need the rotary type phase convertor. I lucked up and found a used and rebuilt 20HP 9 wire Y configuration yesterday. Is this the most popular and best motor to use as opposed to a 12 wire DELTA configuration?

I have done some sizing calculations and a 20 HP motor will do the trick. Who knows about the Y and DELTA configurations and has any experience in building these units?

Any help is appreciated.

[Steved]

It is about time you asked a question!!!

What exactly do you need to know about y and delta connections?

I have not worked with them but I can dust off some of my old text books and give you the theory if that is required.

Let me know and I will search, scan and post (or email)

[HAWK]

Steved,

I ask every now and again. I do want to know the theory in the long run and would love to have any book titles you can supply and /or a few excerpts if possible. The first question I have is will the 9 wire Y config make a better 3 P convertor than the Delta config? I am getting a rocket deal on this motor if I want it, but I have to commit to it on Monday morning: 20HP, 9 wire Y, complete rebuild by trustworthy motor shop with 25 years experience, price at $200 out the door. If I can get a quick answer on this deal, then I want the theory.

[HAWK]

Steved,

I want to buld this convertor to power my ALT 304 on 3 phase to up the 350 amp duty cycle as well as take some strain off the input rectifiers and filter capacitors. The amp draw is near 30 amps at rated duty cycle and I want a little overkill: Not so much as to create a wide capacitance leg voltage variation, but a little extra if I need it. I am also looking into VP TIG and plasma arc equipment. I don't have the specs yet, but I bet 3 phase is necessary.

[Steved]

HAWK:

I understand that this is a great deal but I will not be able to research this weekend as I am not close to my house.

Sorry about that. Let me know if you get an extension on the purchase date and I will do my best to find that information.

Regards,

Steve

[klsm54]

I am not a lot of help on this subject HAWK, but here is a fairly detailed link....3 Phase Convertor.....Possibly more help...Delta vs, Wye Power

[Steved]

Hi Hawk:

Did the best I could with a phone call.

I believe that you are attempting to make 3-phase from single phase with the motor?

I talked with a fellow power sparky and he does not see any problems with either the Y or Delta connection as long as the phase and voltage connections are correct.

He did mention that he has not actually done one of these and without a detailed look at it that was about as far as he was willing to go.

Ideally this would be done with SCRs and some microprocessing for the switching but you are looking for a less expensive version, hence the motor.

Sorry that I could not be of further assistance. Let me know if you still require some excerpts from some power engineering textbooks.

Regards,

Steve

[hankj]

Hawk,

Hope this isn't too late. Go for the "wye" connected motor. For a converter idle motor, it doesn't make any difference as far as genertating the third phase, but there is an additional benefit in that there is a useable voltage available between any phase conductor and the "wye" cneter point. In transformers, that "wye" center point is grounded and represents transformer neutral.

Here's a link to a schematic, if you need one: https://www.homemetalshopclub.org/pr...nv/phconv.html

Be well.

hank

[HAWK]

Steved ; klsm54 ; hankj,


Thank you all for the valuable input. I think the motor is a good deal and being of the Y configuration should serve the purpose well.

[HAWK]

Steved,

Do you have a schematic for a switching MP and SCR based phase convertor? From what I understand the rotary phase convertor should more than adequately supply the 3 phase power I need to run my shop equipment. Am I wrong?

[Steved]

Hi Hawk:

I will search and see what I can find out.

In the end the SCR switching power supply will be more efficient but will be more difficult to build since there will be a PCB to lay out as well as the microcontroller code to write.

I will do a quick search tomorrow to see what I can find.

Regards,

Steve

[Steved]

Forgot to answer the question.

I would guess that this system should work well for your shop assuming that it is small.

This is a big guess since I really do not know how many things you are running at once but by the sounds of it you should be good.

[HAWK]

Steved,

There will be 40 amp draw on 3 phase max at one time. One machine may be at idle while another starts and is running, but will only be running one machine at a time supplied from this 240VAC main.

[HAWK]

Originally posted by Steved
Hi Hawk:

I will search and see what I can find out.

In the end the SCR switching power supply will be more efficient but will be more difficult to build since there will be a PCB to lay out as well as the microcontroller code to write.

I will do a quick search tomorrow to see what I can find.

Regards,

Steve

Thanks.

[Steved]

Hawk:

I have searched the net and have found out some things.

In general the motor method will provide decent (+/- 10%) of line voltage on each phase and depending on your application this may be the way to go.

Agreed that the SCR and microprocessor controlling would be better and would provide better voltage per phase but this method is quite electrically advanced and requires in depth knowledge of rectification and high power flyback circuits.

In general the single phase AC would need to be rectified, turned into a decent DC voltage, and through switching and inductors, turned into a clean 3 phase system. I have a good idea what I am doing and this would take a LONG time to do it properly.

I have found a web site that shows a really nice setup with lots of pictures and step by step instructions that could help you out. You would have to source out components capable of handling your higher power requirements.

http://www.metalwebnews.com/howto/phase-converter/phase-converter.html

I would advise that you stay away from the switching method as it would take up lots of time/money and would take away from your welding.

Finally, to be legal (I have to), I am not endorsing the web page that I have submitted and these instructions are at your own risk. I have not reviewed the schematics in detail and I have not made a professional assesment of them.

Now that is all out of the way, I am interested to see how things turn out.

Let me know if you have any further questions.

Regards,

Steve