Tractorsport Flowbench Forum Archive

Posted: **Sat Jul 11, 2009 1:51 am**

Anyone know anything about building a single phase to three phase power transformer. I think they were called center tap transformers.

I remember studing about them in the electrical apprenticeship program back in 1975.

In my mind I see the illustration from the text book. I just don't remember how to make the tap for the third phase.

Ray

Posted: **Sat Jul 11, 2009 7:56 am**

I have a rotary phase converter I built in my shop for my 3 phase power.

Lots of schematics and detailed instructions on the net for building your own.

Maybe have $100 into mine using a 5hp 3 phase motor. I do not have a starting nor sensing circuit or dropout relay in mine. You can find all sorts of variations. I'm planning on upgrading mine or building another sometime if I find the time as mine is usually running everyday and I can't be without what I have. The cooling fan on my motor broke the other week and I was in a panic trying to find one, had to machine a replacement from another motor as my fan/motor was obsolete.

Posted: **Sat Jul 11, 2009 1:12 pm**

Here are a couple of web sites that may help:

Posted: **Sat Jul 11, 2009 9:50 pm**

Thanks for the Links. Looks like some good info on each one.

Ray

Posted: **Mon Jul 13, 2009 8:36 am**

These days I'd use an Inverter (variable frequency drive)rather than a phase converter. Much smoother!

I'm running a Transwave converter for my Harrison L5 and Bridgeport clone at the moment. It makes the clutch on the Harrison rattle like a Ducati, which is very anoying. When the machines move into their new workshop, they'll go onto inverters.

Posted: **Tue Jul 14, 2009 1:38 am**

This is the maachine I need the 3 phase power for. I'm not sure if it's a 10 or 15 hp motor. No markings or label on motor

Posted: **Tue Jul 14, 2009 6:01 pm**

[color=#000000]Ray, go here They do very nice rotary phase converters. I use a 10hp CNC grade system in my shop and it runs all my machines flawlessly along with creating no issues with the VFD'd i use.

To go from US. single phase 230 to three phase 230 properly is done in two separate operations. One is to use a static conversion to create three separate 230VAc sources 120 degrees out of phase from each other. This static converter must be powerful enough to start the Idler motor. Let use my example my lathe is a gear head 5hp to run this on a rotary converter they recommend 7.5 hp converter system to accommodate the start up load, thus I just chose 10HP. The static converter starts the rotary and the rotary idler motor actually regenerates (induced voltage) the third leg (manufactured phase). A very elegant way of what would take a large single phase motor coupled to a three phase generator.

Why a phase converter over VFD for phase conversion. Yes I am in love with VFD

Posted: **Tue Jul 14, 2009 6:15 pm**

Posted: **Wed Jul 15, 2009 4:18 am**

Ray, it depends on what part of the world you live in.

If you are located in America, then the truly strange and completely unique power distribution system that America has, makes a rotary phase converter both a practical, and a very effective solution.

But if you live in a civilized country (not America) then Motriniman and Jsa are both correct. You will need something a lot more sophisticated than a rotary converter to do the job.

The problem with the internet, is many of us are from entirely different parts of the world with vastly different power distribution systems. What works in California probably will not work in Russia, Europe, Australia, or Central Africa. So be VERY cautious about advice on the internet about mains power systems.

Basically a rotary phase converter is only a solution for people living in America.
The rest of us have a much more difficult problem trying to do this.

Posted: **Wed Jul 15, 2009 4:59 am**

Ok, the power supply in the US is centre tapped 220. If you ignore the tap and just use the two hot wires you have 220 volt single phase, effectively the same as the UK.

Phase CONVERTERS (not inverters) are very simple devices and it's quite easy to make them.

A three phase supply has three sinewaves offset from each other by 120 degrees. A converter uses capacitors to create a phase 'lead' and therefore an artificial second phase. The most a capacitor can shift the phase angle is 90 degrees. In a single phase motor, there is in fact a second winding with a 90 degree shift. This is either just for intermittent use (capacitor start) or continuous (capacitor run), or indeed a hybrid of the two. Even on a 3 phase motor, that 90 degree shift is enough to start the motor. Once the motor is running, it is also a generator and creates it's own third phase as well as dragging the second artificial phase to a 120 degree shift.

The capacitors need to be chosen to match the motor and this is often not a problem, but if you're running a lot of different size motors from the same converter you can get rough running or even overheating. This is where a rotary converter comes in. It is just a static converter with an idle or slave motor added on. Its job is just to generate the third phase and it carries no mechanical load.

If your motors need 415volts then the first stage would be to step the voltage up with a transformer.

I've built converters from the information on this site;

Even if your motor only says 415 volt, you can still re-wire it for 240 by finding and splitting the internal 'star' point.

Posted: **Wed Jul 15, 2009 5:14 am**

Sorry Paul, but I have to disagree on two points.

220 with an available centre taping (three wires) as available only in America, is NOT the same as just having only two wires available with 220 (or 240) volts between them.

And a conventional 415 volt three phase motor normally has no central star point. It usually has only three 415 volt windings connected in delta, and only three wires coming out of the motor.

Posted: **Wed Jul 15, 2009 4:50 pm**

[color=#000000]Ray,

By doing a lookup on your positing IP address I can see you live around Jackson Mississippi.... I think that is in the United states. But since i live just south of the Mason Dixon you probably still think I

Posted: **Wed Jul 15, 2009 7:22 pm**

To clarify my earlier post, I'm talking inverter, as a broard term that covers more than just VFD's.

Tony,

Readilly available 3 phase motors up to about 7.5kw have changed in recent years. They are typically 230V delta 400V star these days with 6 wires to the terminal block. This has come about with the worldwide 230v/400v harmonization and manufacturers realising one part can serve in multiple locations.

Ray,

For a single machine I can't imagine a replacement motor would be more expensive than a rotary phase converter. But then the static and idler rotary converters just look dodgy to me, probably due to indoctronation at a youug age ???

Posted: **Wed Jul 15, 2009 8:27 pm**

To All,

Thanks for the valuable information you have given me. Thank you for reminding me we're all from different parts of the Globe. I understand we all have differences in power systems due to locations.

I am located in Pascagoula, Mississippi. On the map of the United States I am located on the left hand side of the Alabama/Mississippi state line where it ends at the Gulf of Mexico. I know I didn't need to add all this information, but I did for anyone courious.

The question was ask if I was doing diesel heads. No sir, I found it and an Index Model 55 Verticle Milling Machine for a price I couldn't refuse.

I contacted Peterson Machinery and was able to optain a copy of the original manual at no charge. The manual covers all models of the surfacer. That's where I got the information on the different HP ratings of the motor. They've even contacted me on occasions to offer help or ask if I needed supplies.

The motor label plate with horsepower rating, etc.. is not on the motor. I think it is a model 1057 because the length of travel for the surfacing wheel is 67 inches.

I'm going to read the power requirement section of the manual again to refresh my memory. There were several things brought up that I'm not able to answer.

Thanks again for all the good information,
Ray

Tractorsport Flowbench Forum Archive

Three phase power - Single phase to three phase transformer