XPost: sci.electronics.design, sci.electronics.misc, sci.electronics.repair   
   From: jamie_ka1lpa@charter.net   
      
   In article <0001HW.D11E991C05E771E8B01029BF@news.eternal-september.org>,   
   pconners98@gUSmail.com says...   
   >   
   > 180 vdc, 1 hp, pm motor.   
   >   
   > with dmm what should be the first tests? motor is in a difficult location to   
   > examine visually so i'd like to start with electrical evaluation.   
   >   
   > it measures 1.2 ohms between the 2 armature leads.   
   >   
   > thanks.   
      
   those kind of motors tend to have mechanical issues..   
      
   Bearings is common which causes a tight turning shaft   
   and may cause the armature to move around on the brushes.   
      
    Also, a bearing could be completely blown out and the motor   
   will still make attempts to turn if the brushes are still making   
   contact.   
      
    Another issue is the PM's some times fall off, lose their bond to   
   the outer shell and come in contact with the rotor.   
      
    Then you get the occasion of weak magnets due from too many hours of   
   running hot, which causes more Arm current and lack of torque but with   
   higher RPM abilities.   
      
    Now and then, the armature windings may short to each other but not to   
   ground. Most of the time megger meters will not reveal this defect but   
   usually signs of over heated wire is a good bet.   
      
   Also, if you manually spin the motor it can act as a generator..   
      
   Disconnect the leads to the motor and see if it turns freely, if so then   
   you most likely do not have mechanical issue.. Now connect the ARM leads   
   together from the motor and see if you get heavy drag (Dynamic Braking)   
   due to energy being generated and short via the A1 and A2 leads. If you   
   do get a got drag on it, chances are it's of.   
      
    When checking the brushes via the DMM, you need to turn the motor very   
   slowly so that you can account for all the armature bars, you may have a   
   set of scorched  brushes.   
      
   Jamie   
      
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