Mark, My first reply from May 8th:
"Hi Mark, My first thought is damage or a discontinuity to the commutator surface. This can be checked with a dial indicator. If found, lathe turning may be needed. Also check for high mica. The other things to check are all electrical connects and spring pressures. Make sure all brushes slide smoothly in the respective holders. Jeff M." You are marking invalid assumptions. Noticeable rapid and uneven brush wear rate is an indication of a problem which you are not addressing. Jeff M ________________________________ From: Mark Hanson <[email protected]> To: "[email protected]" <[email protected]> Sent: Tuesday, May 14, 2013 4:27 PM Subject: [EVDL] Uneven brush wear Hi Jeff etc, Maybe my milli-ohm meter that measured .2 milli-ohms was off but all 4 rear brushes are wearing down fast and the front one's no wear at all - so that's the only explanation I can come up with is non-symetrical brush bars. The ADC motor brush rigging are symetrical . I guess it's no biggee, I can change brushes fairly quickly now, just let the rears wear down in 3k, then the fronts will start conducting for another 3k miles. I'm just used to taking motors for granted, never bothered with brush replacement till about 100k miles in the past. The brushes that seat first start shunting away the current from the others and then it's a positive feedback loop, the shorter they get the more current they pull. best Regards, mark Hi Mark, I think you're barking up the wrong tree.? My calculations for added resistance of the extra buss bar length to the inside brush connection at 20 degrees C is 0.01 milliOhms.? That only carries one fourth of the armature current so represents 1.25 millivolt drop at a 500A load on the motor.? The typical voltage drop per brush at that current would be on the order of several volts.? So the voltage divider method would indicate a possible current imbalance of a tenth of a percent due to the extra copper bus bar length.? Another thing to consider is the fact that the rear brushes sit on the comm further away from the armature so the current flowing through them has a longer path through the commutator segments to reach the armature circuit.? This kind of counteracts the shorter path from the A terminals to the rear brush. In both cases you're talking about a short distance though a relatively large cross section of low resistivity conductor which results in negligible voltage drop compare to the rest of the circuit. You mention 100K miles on your Prestolite and it had a similar brush connector bus bars (coming from the opposite way).? Did those show uneven wear?? I think your current problem is not associated with that small distance difference in the brush connectors. Jeff M -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20130514/6325964a/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20130514/f680edc3/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
