3 phase motor?

Thanks for the tips. I will look into that. I also omitted that I need 550 volts to tun this baby.

ken O

Yes, it is called a phase converter. Converts single phase to three phase.

There are two kinds, electronic converters (which often are just there to help start 3 phase motors and then switch them to single phase AC), and rotary phase converters (RPC).

Rotary phase converters rely on the fact that

1) a 3 phase motor, if spun up, would continue spinning on single phase only 2) Such a motor, while spinning, generates magnetic fields that produce phase shifted voltage in the third leg.

I built a homemade RPC for just $45 in used parts, see the story, reference information etc

It's really a one evening project once you have all the parts.

You would later find that buying all necessary wires and cables, disconnects, etc to both supply power to the RPC, as well as to deliver power to 3 phase devices, would be much more costly and time consuming. But, proper wiring is a must! (and you would do the same with commercial phase converters that you buy)

I use my phase converter a lot. Having a decent RPC allows you to buy high quality, used industrial machinery for very low prices compared to single phase stuff.

For example, my 3 phase TIG welder cost me only $9.99:

i

Buy one. It is possible, but doing it with good power factor correction, and safely, is hard work, and will involve a lot of time. Even on commercial units, there are two basically different types. The type needed will depend on the actual layout of the motor. The simpler/cheaper type, does it in solid state, and is dependant on a motor that has star windings, not delta windings. The second form includes transformer coupling, or a rotary converter, and is more expensive. Units are made by companies like LG, Toshiba, Westinghouse, Hyundai etc.. Look at:

Generally the better units, also offer you the option of operating the motor at different speeds, and ramping acceleration/deceleration as well, giving more flexibility, and less droop on the incoming supply when starting. You could not even buy the parts to build such a unit, for the prices they sell for, especially on places like Ebay.

Best Wishes

It is not at all difficult, I did it basically in two evenings (I was interrupted by family and had to ask questions on newsgroup).

My 10 HP rotary phase converter cost me $45 in parts. Granted, I am pretty good at getting stuff cheaply. For a more regular person, who would buy a used 3 phase motor for about $5 per HP at a local scrap company, and caps on ebay, the cost would be about $80 or so, plus electric wiring costs -- all those cables, circuit breakers etc, that you have to buy regardless of whether your RPC is homemade or store bought.

This is a perfect home project where not many things can go wrong that are not easily corrected.

i

These days, it is simplest and best to buy a three phase variable frequency drive that is single phase powered.

A typical three horsepower 220 volt unit now only costs around $300 and is ridiculously smaller and lighter than building up your own.

We have smaller units in stock at bargain prices.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
Synergetics   3860 West First Street   Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml   email: don@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com

that makes some difference:)

What is the baby actually -- what is the device that you need to power, and what power source do you have available at your present location?

i

ig has already given you one answer. You might try a google search in rec.crafts.metalworking-- this question often comes up for motors of a few HP on "old iron" machines that people want to run in their basement (or garage for those who must do without).

There are basically three approaches--

Rotary phase converter- an idler motor, often with some added capacitors, that essentially operates powered off of one phase and generates the other two. You get most of the available torque, especially with the proper capacitors. A simple electrical circuit or a small starting motor is used to get the idler spinning. Line frequency only. This is a good approach if you don't mind lugging around some scrap iron as you can often get the 3-phase idler motor basically for free (it has to be rather larger in HP than the largest motor you wish to run). I bought a 10HP/240V one for $150 delivered, but that was for a brand new Baldor- a bit of a bargain because it was nameplated at 50Hz.

Static phase converter- uses phase shifting (passive components) to create the other phases. Gives only partial torque. Line frequency only. Not really recommended.

VFD - the incoming single phase power is rectified and filtered, and three-phase power is generated from the DC rail using three half-bridges. You get to set the frequency over a range so you can vary the speed of your motor, plus a nice digital display etc. It's a bit harder on the motor insulation than just running it from the line, but well-designed motors should be okay.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Yes, but most converters have not tended to be very good. I've never built one, but have heard a lot of problems exist.

You have 4 options

1) Investigate if its possible to get a 3 phase supply to your house.

99% of houses in the UK have single phase, but mine has 3 phase, which was installed due to the power requirments of "economy 7" electrical storage heaters. There is no extra standing charge for having a 3 phase meter. You may well find it can be installed for zero cost. Admittidly its not likely, but I would investigate.

I don't have any 3 phase consumer unit, but if you want to run 3 phase kit, you will find those are not cheap like normal domestic ones.

2) Build/buy a converter.

3) Replace the motor with single phase. This is often the most economical solution. If the motor is too big to run from single phase, then I suggest you take route 1 and get a real 3 phase supply.

Well, I have built one, and it works just fine, within the limits of its rated power.

Building a 10 HP phase converter is cheaper than buying a 5 HP single phase motor. I built the former and resold the latter, that's how Iknow.

i

Yes. Yours is a rotary converter, which is really easier to do 'safely', than a solid state unit. For most likely motors, depending on the competence of the poster, this could well be an 'option'.

Your buying skills are obviously pretty good. :-)

Best Wishes

And note that it produces an almost perfect sinewave in the third leg (perfection dependent mostly on current draw vs. idler horsepower), and not some weird waveform.

Even with not so good buying skills, a homemade RPC is an obvious winner.

i

call the electricty supply company and say "I'd like to convert to 3 phase elecricity" have your cheque book handy.

It'd probably be easier to replace the motor with a single phase motor.

Bye. Jasen

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http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLD,GGLD:2004-42,GGLD:en&q=3%2Dphase+converter

Why is it harder on the motor insulation?

--
 Thanks,
    - Win

I am not a big expert, but I think that square wave produces move vibration in windings due to its sudden rise, and hence can damage insulation in the long run.

I think that nothing beats a true sinewave for which the motors were designed...

A rotary phase converter is superior from all performance aspects: it can run many machines at once, with the electricity that they were designed for.

i

Inductance in the wiring to the motor allows spikes and ringing at the motor itself:

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I'm puzzled, because in an H-bridge, or half-bridge, the motor isn't released for uncontrolled ringing, because one device or the other is on, or a clamp diode is on, limiting any flyback voltage. The waveforms in the paper look like a simple single FET with no clamping, which isn't what you get with a VFD controller drive.

--
 Thanks,
    - Win

The problem with VFD is that single phase high power to dc conversion is much more expensive than three phase high power to dc conversion.

Filter capacitors have to be much larger with lower ESR. And input power waveform spikes are obscene unless PFC treated.

Also, you will need three times the current on a single phase line. Probably meaning a major capacity upgrade.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
Synergetics   3860 West First Street   Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml   email: don@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com

Because the waveforms typically suck.

See

for a better solution.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
Synergetics   3860 West First Street   Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml   email: don@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com