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phase converter

Started by slider, August 04, 2011, 12:16:56 PM

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slider

I  was thinking of making a phase converter out of a 3 phase motor.It is my understanding that you need a somewhat larger motor to create the third leg,3 to 5 more horsepower than the one you are converting to.My question is can you take a 25 horse motor and use a 25 horse motor for the pony motor ? This is going a minor edger that im not going to be using to full capacity .Sorry to ramble but I can get a deal on this 25 motor and it would be great to get this thing converted without spending an arm and a leg. thanks ,al 
al glenn

jason.weir

how big is the motor on the edger?  You can buy VFD's (variable frequency drives) pretty cheap if the HP requirement is low - cost to properly build a 25hp rotary phase converter is significant even if you have a free motor...

-J

bandmiller2

Slider,I've been running a milling machine with a phase converter for years.Google it theirs several good writeups on making a rotary converter.It helps if you have an amp probe you know that clips over the wire then you can juggle the capacitors to ger equal power to each leg. Frank C.
A man armed with common sense is packing a big piece

bandmiller2

Slider I ment to add your probibly all right to use the 25 to run the edger if your not using the motor to capacity. Read up first their are some types of motors that are better than outhers. Frank C.
A man armed with common sense is packing a big piece

Larry

Nobody can answer your question with a firm yes or no.  Way too many unknowns.  I usually figure the converter motor needs to be twice the size of the load to start properly.  Never had a problem.  If it don't work I supposed you could add a motor.

I've been balancing the phases on the last couple I built and they seem to start higher hp motors than anticipated.  Not for sure if that was luck or my injuneering skill. :D

Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

sealark37

Considering that you will be starting the edger more or less unloaded, your 25hp idler will work fine.  practicalmachinist.com has a whole section on RPC design and construction.  I am not a electrician.  I built my own out of parts I found at the dump or cheap used stuff.  You will save lots of time if you can find someone local that has put one together.  Mine works flawlessly.  The electrician who connected it to my panel stated flatly that it would not work.  After he saw it run, he declared that it was a new one on him.  He has 40+ years experience.  Good luck.  Regards, Clark

shelbycharger400

i dont know wich ones they are, but you need to know the voltage on the motor, some are not compatable to use as a rotary converter.


sparky

You will be needing a quantity of electrolytic and oil capacitors to build a phase converter. It involves a trial and error method for sizing the capacitors for proper operation. Electrolytics are needed for starting, and the oil capacitors perform in the running mode. The output voltage and current will not be perfectly balanced, but a converter will drive
your edger.

Sparky
I'tnl 2050 with Prentrice 110, Custom built 48" left-hand circular and 52" Bellsaw right-hand circular mills, Jonsered 2171, Stihl 084, and too many other chainsaws. John Deere 3020 and Oliver 1800 with FELs. 20" 4-sided planer and misc.

kelLOGg

When I built mine, I recall the guideline of the idler 3ph motor being 50% greater HP than the motor being operated (easy to achieve for a single motor operating at a time), and there is range of capacitance/HP for the running capacitors - but I can't recall that value. I remember the web sites already mentioned and they will have that info.
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slider

thanks for the advice.I will pass this on to my electrician friend and see if he wants to take a wag at it.  al
al glenn

bandmiller2

Slider,old air conditioners are a good scorce for large capacitors. Frank C.
A man armed with common sense is packing a big piece

mikeb1079

QuoteSlider,old air conditioners are a good scorce for large capacitors. Frank C.

as are streetlights.  if there's a city or county maintenance shop around they'd probably let you have some, that's how i built mine.  mine also worked flawlessly but i used a 5hp idler motor to power a 1 1/2 hp running motor.
as others have said, there are many good websites devoted to this.
good luck!
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shelbycharger400

make sure they are the ones you want.  some capacitors are oil filled, and some considered hazardous waste.

r.man

I have had numerous people over the years tell me something won't work or that I can't do something. Most of the time they are wrong so I stopped listening. The websites that I have read seem fairly straightforward about the rotary converters and I plan to build one soon for a nephew. My advice from experience would be to start the unit from a safe distance when testing and make sure the steel enclosure is closed during startup. Problems with electrical circuits sometimes result in small explosions which have minor consequences if contained. Most of the time smoke and ruined parts are the only result of a wiring mistake.
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