On 26 May, Johnny Billquist wrote:

> Huh? How do you rewire a three phase motor for single phase???
Connect two of the motor phases to the single phase and neutral and the
third motor phase via a capacitor to the single phase or neutral. The
size of the capacitor depends on the power of the motor. Note: You
allway loose some of the power of the motor. 

Of course you can also use an electronc frequency transformer. This is
somthing like an "online UPS with three phase output and without battery". 

> Single phase motors are quite different in design.
Not that many. In a three phase motor you have three coils splitted in
an upper und lower half. This results in a total of six coils in an
angle of 60 degrees. 
In a single phase motor you have one coil splitted in two halfs in an
angle of 180 degrees, and a "helper coil". 
In a three phase motor you have (from the three phases and the three /
six coils) a rotating magnetic field. The strengthnes of the field is
constant, the direction just spins around. 
In a single phase motor you have a alterning field. It does (normaly)
not spin around. The strengthnes of the field follows (including sign)
the sine wave of the feeding current. With this, the motor can not
start. The field has no direction. Here comes the "helper coil" into
the game. It is placed in 90 degrees to the main coil and expands the
alterning magnetic field to an eliptic rotating field. Thus the motor
starts.

This is for asynchronus machines. Perhaps you call a "universal" motor
a single phase motor. Then you are right. A "universal" motor is a
complete other design using a "Kollektor" (how is it called in
English?). 
-- 



tschuess,
          Jochen

Homepage: http://www.unixag-kl.fh-kl.de/~jkunz