We have two DC motors that wear the brushes out about every 3 weeks. What would cause this? The commutator "looks OK". Thanks for any suggestions.
Some more details would be helpful. Specs on the motors. How long have they been in service and what is the application.
If the brushes are all wearing evenly then I would look into changing to a different brush that will carry a higher current density in your application. Are all of your brushes wearing evenly?
If the commutator is OK then as Steventyj suggests look at the brush and ensure it is the correct type for current density, hardness etc. Also check the spring tension if wear is uneven chances are that is the culprit.
Your brush supplier should be able to answer about 90% of your questions and resolve this for you.
THE TYPE OF BRUSH IS MOST IMPORTANT. YOU CAN CHECK THE SPECIFICATIONS GIVEN BY MOTOR MANUFACTURER AND ACCORDINGLY YOU CAN SELECT THE CORRECT TYPE OF BRUSHES AS SUGGESTED VIDE EARLIER POSTS.
Buhsman:
Looks like everyone is leading you in the right direction, but I wanted to take a single shot in the dark. Are you using any type of sealant on the comm covers or anywhere exposed to the brushes? Silicone and other sealants can significantly decrease brush life. You may already know this, but no one else has offered the suggestion. I've seen stranger things.
Good luck!
Buhsman, try an advanced keyword search using the all words option at this site for "brush wear" [without quotes.] It returns about six applicable threads on the matter. The point is, in the last two years there have been probably 30 posts on the subject that will save some waiting {and typing.}
Suggestion: Also, the angular adjustment of brush braces needs to be checked. An improper angle could cause excessive sparking and the premature brush wear-out.
The commutator surface may look reasonably good; however, the mica between lamellae is supposed to be somewhat removed, so that there is a small groove, to avoid the brush bouncing on the commutator due to protruding mica.
You don't give any details about the motors, other than the fact they are DC.
You don't mention how long have these motors been having brushe changes at 3 week intevals.Have the motors just started doing this after a recent repair ,or is it an old probblem ?.If it did run well at one time,than any change to brushe types or repairs may have caused that.
We just started a large Dragline where we had changed 4 Generator stators.We performed PVNs on the 4 Gens and all appeared OK.After running for awhile, one of the Gens started sparking considerably.Not orange sparks, but a white kind of spark.We will have to redo the PVNs.
If we don't the brushes will wear pretty fast.
Do you have any sparking?Is ambient humidity and Temp normal?
Is there selective brush wear?.I mean one brush down to the pigtail and the others like new?
A lot of variables in here.
I would look for any recent changes to the motors or brush
types.
