Universal motor arcing 1

[kachman]

I'm trying to investigate an issue where arcing in newly constructed universal motors is a problem. I'm breaking down the causes of this defect to the different components (Armature, brushes, fields) and causes(poor comm finish, brush grade etc) and would appreciate any ideas on the most common reasons why a motor would emit excessive sparks at any point.

 

[SteveKW]

The most common I run into are...
Poor brush pressure against the commutator.
High spots on the commutator.
A shorted commutator.

 

[RadarRay]

Having the brush holder not zeroed is a good reason. Perhaps not that common, but most electical maintenance personnel are unaware that a Shunt wound DC motor has a zero point. If for some reason they get into the motor to do maintenance and move the holder, they are in trouble.
Also, although I have never experienced it personally, when running DC motors over base speed the current limit should be reduced. I believe this is common, or was common, in the machine tool industry. I have seen drives which have parameters to allow this, although the machine tool industry is not my area of expertise.

 

[jbartos]

Suggestion: The second posting probably implies by "high spots on the commutator" some isolation mica between commutator lamellae may be somewhat lose or higher causing the brush to be lifted and consequently creating arcing.
Also, the previous posting addresses the reaction of the armature to be properly accounted for by the correct adjustment of brush braces.
Finally, some arcing sparking will always be present; especially, it will be noticeable when the motor is fully loaded.

 

[ognen]

There are a few reasons for that:
- are stator windings correctly calculated?(important)
- is comutation axis in line with brush holders ? (very important)
- are armature windings with correct angle ?
first of all if motor is new, then why dont you use some LITOLIT or other manifacturer stones for comutator, and brushes take the radius of comutator.This may be a little trick that constructors of these machines are used to do (as myself).Usually pressure of brushes is good if they are not used.Other reason is shorted comutator( there is not any arc but comutator flames over all comutator). If this is true then try to clean comutator holes with metal brush.
Last reason for arc is brush holders angle,hardness of conection between brush holders and stator laminates e.t.c.If you are not constructor, sorry I can't help you with this problem.

 

[TeraVolt]

Hi kachman,
Du you think about universal motors like motors in electrical tools (drillers, grinders etc.)?
The most of this motors have more or less arcing in normal operation, because they have no interpole windings. Reason for that: Cheaper in construction.