From: nospam@null.void   
      
   On Fri, 12 Jul 2013 11:29:04 -0700, Salmon Egg wrote:   
      
   > In article ,   
   >  moroney@world.std.spaamtrap.com (Michael Moroney) wrote:   
   >   
   >> stryped1@yahoo.com writes:   
   >>   
   >> >I found a Hunter DSP 9000 wheel balancer I would like to have for my   
   >> >home shop. The problem is it is 230 volt three phase. I only have   
   >> >single phase available to me.   
   >>   
   >> >Can anyone tell me if a static converter would work for this   
   >> >application or what is the cheapest esiest way to make something like   
   >> >this work?   
   >>   
   >> >I appreciate it!   
   >>   
   >> The cheapest way I know of is to get a surplus 3 phase motor larger   
   >> than the one in the balancer and some trivial components (like a motor   
   >> starter capacitor).  The surplus motor is powered by the single phase   
   >> 240V feed and acts as a generator, generating three phase. You just   
   >> connect the A B C phases of the load to the A B C phases of the motor.   
   >>   
   >> I don't remember any further details, but Google is your friend.   
   >   
   > Although I am a bit rusty on the subject, I believe this will not work   
   > with induction motors. An induction generator requires a source of (what   
   > I think is leading) reactive power that it normally gets from the grid   
   > it is connected to.   
      
   Rotary converters based on standard induction motors should include   
   capacitors between the single phase line connected motor terminals and   
   the derived phase motor terminals, also sometimes a power factor   
   correction cap across the single phase line.  One design I have seen   
   posted on the rec.crafts.metalworking newsgroup used a 5 HP motor with 60   
   uF and 50 uF capacitors to the derived phase, with an additional ~300 uF   
   motor start capacitor temporarily connected across the 60 uF run cap for   
   starting. and a 50 uF power factor cap across the line.  Current and   
   voltage balance will never be perfect with a rotary converter based on an   
   induction motor with capacitors, but it is good enough to power 3-phase   
   motors in a home shop where the motors are not generally run continuously   
   at full power.   
      
   There are a number of variations on the rotary converter in use including   
   use of fixed capacitors large enough to start the load without a starting   
   capacitor, and the rope-start converter where a rope wrapped around the   
   motor shaft is used instead of the starting capacitor.  The rope-start   
   version will even run and power a smaller load with poorly balanced power   
   without any capacitors at all; the single phase line provides enough   
   reactive power to keep a lightly loaded 3 phase induction motor running   
   once it has been started.   
      
   Better rotary converters use a special multi-tapped single phase   
   transformer with a non-standard induction motor winding to produce very   
   well balanced 3-phase power using no capacitors.  This design was once   
   widely used in electric locomotives, and is described in detail in   
   "Principles of Alternating-Current Machinery" by Lawrence and Richard,   
   4th ed 1953 (the classic book on the subject).  I don't know if these are   
   still made but I have seen them show up at auctions occasionally.   
      
   The static converter is a box of capacitors only, using your motor(s) for   
   the other half of the converter, suitable for powering motor loads only   
   and typically even more imbalanced that a homemade rotary converter - but   
   also cheaper to build yourself and often well suited for the home shop.   
      
   The VFD is also designed for driving motor loads only, and some care must   
   be exercised when using them with standard (not inverter rated) motors,   
   however if mounted very close to a 240 volt motor (short wire from   
   inverter to motor) or if the optional output filter is purchased with the   
   VFD (or better yet use the output filter and a very short cable for   
   minimum chance of EMI problems, possibly also use the optional VFD input   
   filter if sharing a power feed with sensitive loads), and the motor is   
   never run at reduced speeds except during ramp up to 60 Hz on start and   
   ramp down on stop, and good wiring practices are followed to keep VFD   
   noise out of the control system, then the VFD will provide the motor with   
   well balanced 3 phase power and operation as good as with a utility 3-   
   phase feed can be expected.   
      
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