XPost: rec.crafts.metalworking   
   From: depucca@att.net   
      
   In article    
   "Lloyd E. Sponenburgh"  wrote:   
   >   
   > Ignoramus26083  fired this volley in   
   > news:If6dnStz8dp0vRXPnZ2dnUVZ_sCdnZ2d@giganews.com:   
   >   
   > > But can this motor somehow excite itself to generate electricity?   
   >   
   > Short answer, "No."  Not unless it was a permanent-magnet motor or had a   
   > wound armature fed through slip rings or a commutator.  There has to be   
   > something to excite the fields initially.  Common AC motors use reverse-   
   > EMF in the armature to repel the fields, but the armature gets its   
   > excitation from the field windings.   
   >   
   > So-called "universal" motors can act as generators, so long as they   
   > either retain some residual magnetism in their fields, or have a DC   
   > supply to provide excitation until they can supply their own through a   
   > rectifier.   
   >   
   > Lloyd   
      
   Better answer, depends on the motor design.   
      
   Technically any motor can act as a generator, but efficiency   
   will likely not be optimal.   
      
   Locomotives use their traction motors as generators to energize   
   dynamic braking systems for example.  If the motors and   
   resistors were 100% efficient, they could stop a train without   
   using brakes, but that isn't the case.  They do generate quite a   
   bit of energy though, which is dissipated as heat.   
      
   As you say above, something must excite the fields.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)