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| | | | Joined: Jun 2008 Posts: 1,388 Shop Shark | | Shop Shark Joined: Jun 2008 Posts: 1,388 | So, I rebuilt my starter over the weekend, and I was wondering what the brushes were made of. I had always figured that they would be made of carbon, or graphite or such, but they really look coppery, and feel metallic. I'm sure they aren't copper, are they some kind of compressed mixture?
Thanks all.
| | | | | Joined: Jul 2001 Posts: 3,887 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Jul 2001 Posts: 3,887 | usually sintered copper-graphite [compressed carbon/copper powder] I believe - used to be lead as well, might still be Bill | | | | | Joined: Jun 2008 Posts: 1,388 Shop Shark | | Shop Shark Joined: Jun 2008 Posts: 1,388 | Thanks Bill, that makes sense. | | | | | Joined: Jul 2007 Posts: 461 Shop Shark | | Shop Shark Joined: Jul 2007 Posts: 461 | Sintered bronze, I believe, which has a lead component. But that may have changed with all the concern over lead.
The commutator doesn't get undercut on starter armatures as it would with carbon brushes. Carbon brushes are used in generators, alternators and small motors.
Harvester | | | | | Joined: May 2008 Posts: 40 Apprentice | | Apprentice Joined: May 2008 Posts: 40 | Sintered copper and carbon/graphite, 24v starter brushes have a higher carbon content and are much blacker, copper was added to make them wear longer, I have not heard of any that contain lead except very old brushes maybe but it would be a very low % as when the lead gets hot would cause brush fracture and flaking. | | | | | Joined: Jul 2001 Posts: 3,887 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Jul 2001 Posts: 3,887 | Harvester - I think you'll find sintered bronze is used primarily for bearings/bushings, due to it's porosity, which holds oil well - would get plugged up easily on a starter motor or generator
Bill | | | | | Joined: Aug 2009 Posts: 295 Shop Shark | | Shop Shark Joined: Aug 2009 Posts: 295 | All commutator bars on all DC motors and generators are insulated using mica. The mica is ALWAYS undercut to avoid brushes bouncing. The copper specks in your brushes are to give longer brush life but at the expense of commutator life. If you can get carbon only I think you would be better off. Brushes cheap commutator expensive comparitively.
Dan Bentler | | | | | Joined: May 2008 Posts: 40 Apprentice | | Apprentice Joined: May 2008 Posts: 40 | leitmotif just brought up another subject, nearly all new starter armatures do not have under cut mica. They are intended to operate this way and It may have something to do with the copper added to the brushes maybe is to wear down the mica as its used. generator armatures should be under cut due to there higher speed and constant operation. Take the end off a new starter, right or wrong many are not undercut at all.
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