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Tool Talk Discussion Forum

3 phase versus single phase

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Howard H.

10-12-2007 09:34:32




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I'm looking at buying a woodshop full of equipment - but two of the pieces are 3 phase.

Is a motor swap the only way to convert a 3 phase device back to single? Or can the motors be rewired?

We've used rotophases on irrigation sprinklers to create the 3rd leg, but that wouldn't be practical here.


Thanks,
Howard




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Pycoed

10-13-2007 10:42:28




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 Re: 3 phase versus single phase in reply to Jerry (KS), 10-12-2007 09:34:32  

Joe(TX) said: (quoted from post at 03:03:29 10/13/07) I am curious as to why you feel the rotophase would not be practical.

An advantage to the the VFD is the motor speed control which is what they are made for. Not all VFD's will take a single phase input.

I built a phase converter myself. I have also used the rope start method.


Have a look on Ebay for VFD's. I have only single phase in my workshop & used to use capacitors to run a mill with a 3 ph motor. Worked OK, but was a bit down on power, then I got a VFD (around 50 UK pounds ) - WHAT a DIFFERENCE The speed control alone is worth it. I was so impressed I got another three & changed the motors on two lathes from single to three phase just to use VFD's on them ( you can pick up 1 to 3 HP three phase motors here for next to nothing). I even put one on a drill press, now I have a super slow speed reversing tapping machine - press was �20, VFD was �15.

USE a VFD!!

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n9lhm

10-13-2007 05:22:02




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 Re: 3 phase versus single phase in reply to Howard H., 10-12-2007 09:34:32  
My whole metal machine shop in my basement runs on three-phase. There"s no comparison, motors start/stop/reverse instantly, and they are SO much more efficient. I can run my power-factor-corrected rotophase and ONE 3/4 horse three phase motor and pull less current off the main line than ONE 3/4 horse single-phase motor.
And why are you guys pony-starting these rotaries? Another set of caps and a starting relay and they start themselves when you turn them on. My 5 horse rotary is up to speed in seconds, and it isn"t any more work or expense to add a few caps and a relay than to build up a pony starter (extra motor, belts, pulleys, etc.)
Write me if you have any more questions.
Brian

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Joe(TX)

10-12-2007 18:03:29




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 Re: 3 phase versus single phase in reply to Howard H., 10-12-2007 09:34:32  
I am curious as to why you feel the rotophase would not be practical.
An advantage to the the VFD is the motor speed control which is what they are made for. Not all VFD's will take a single phase input.
I built a phase converter myself. I have also used the rope start method.



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VaTom

10-13-2007 04:24:38




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 Re: 3 phase versus single phase in reply to Joe(TX), 10-12-2007 18:03:29  
Joe(TX), if you tire of that rope you can put a chain gear on your motor shaft. Can easily kick it fast enough to start the dummy motor. Just make sure you kick it the same direction each time (the motor doesn't care, but you will).

That's my setup, which I prefer to adding the 120v motor. Had that once. I've got the capacitor wiring diagram for a 3hp unit if anybody's interested. Too small for me, but I made one for a guy down the road who simply flips a switch.

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Howard H.

10-12-2007 20:20:38




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 Re: 3 phase versus single phase in reply to Joe(TX), 10-12-2007 18:03:29  

Hi Joe -

Thanks for all the advice, fellows...

The rotophases we use have been about 200 pounds and take a full minute or so to wind up and wind down when you fire them up.

Plus, on one set of sprinklers, for some reason, we had a terrible time keeping the rotophase cool enough. The electrician we had helping us was as experienced as anyone in the area and he couldn't figure out why they kept heating and eventually failing.

We chalked it up to intermittent voltage drops since we were near the end of the line with an 80,000 head feedlot nearby, but we didn't know for sure if that was the problem.

Anyway, I just thought it might be overkill for a woodworking shop...


Howard

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JMS/.MN

10-12-2007 12:18:37




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 Re: 3 phase versus single phase in reply to Howard H., 10-12-2007 09:34:32  
You can make a phase converter using a 3 phase motor and a small single phase to spin it. 3 phase motor generates the third phase that you need, after the single phase gets it spinning. Made mine from excess parts- runs a milling machine, hacksaw, and eight foot turning lathe. Go to www.homemetalshop.com for details on how to build one, or order plans from Lindsay Books. I mounted mine on wheels, put 4 conductor cords on each machine- wheel it to whichever one I need to use.

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JMS/.MN

10-12-2007 12:22:54




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 Re: 3 phase versus single phase in reply to JMS/.MN, 10-12-2007 12:18:37  
What Mike M, below is talking about- he started the 3 phase motor spinning by using a rope- mine has a half horse single phase on a hinge, belted to the 3 phase to get it spinning. Once started, the single phase gets shut off. Everything was built from my scrap pile.



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Bob

10-12-2007 10:12:12




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 Practical Machinist in reply to Howard H., 10-12-2007 09:34:32  
Practical Machinist has a WHOLE MESSAGE BOARD of how to convert or power three-phase machinery using staic converters, rotary converters, or "VFD'S.



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John T

10-12-2007 10:07:08




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 Re: 3 phase versus single phase in reply to Howard H., 10-12-2007 09:34:32  
For only a couple (if smaller) motors Id just swap motors but if I had a bunch of motorized equipment especially larger HP then Id use a roto phase to run it all on 3 phase (more efficient motors)

John T



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Mike M

10-12-2007 09:43:09




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 Re: 3 phase versus single phase in reply to Howard H., 10-12-2007 09:34:32  
I have a 3 phase mill and a lathe I run with a small box type phase converter.Price isn't too bad on the smaller hp units. Got it from Wholesale Tool and it does a good job. I used to use an old 3 phase motor and get it going with a rope start it worked but was a pain in the rear but CHEAP.



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CWL

10-12-2007 09:39:51




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 Re: 3 phase versus single phase in reply to Howard H., 10-12-2007 09:34:32  
Motor swap.



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