On Sun, 3 Jun 2012 09:17:36 -0700 (PDT), klem kedidelhopper
wrote:
I have an AF300 engine and tender I just repaired with several new
parts I got from a vendor at the last local show.
Oh-oh.
http://www.hobbysurplus.com/xviews/300s1pcHSS.asp
I disassembled the rear of the motor and removed the armature.
Remove the wires from the motor contacts, attach an ohmmeter to the
motor leads, and SLOWLY rotate the armature. Rotate one commutator
segment at a time. What you're looking for is momentary short
circuit, or an imblance in the winding resistance (shorted turn). If
you get a short, then someone stuffed in the wrong size brushes. If
the measurements are very erratic, the brushes might have low spring
tension. If you get different readings on one commutator segment, you
have a shorted turn. Also, try running the motor outside the engine
to see how it runs.
I had
noted on my initial repair that the armature commutator was slightly
scored and somewhat blackened in a circular pattern where the brushes
rotate.
That's fairly normal.
In addition I re soldered the three
armature wires to the commutator segments, as the solder looked a
little sparse.
Careful that you don't unbalance the armature with too much solder on
one terminal.
I set the chassis up on test blocks and ran it at slow speed.
Initially it ran very smooth, however I could see a very slight arc
coming from one of the brushes.
Only one brush? It should be sparking equally under both brushes. Are
the brushes curved to fit the commutator shape? Is one brush
different? Are the commutator sections pitted? Are the brush faces
pitted? Are they the correct size and tupe of brushes?
I have noticed this on many motors in
the past, and since it was so minor I didn't give it much thought. My
goal was to run the engine for a period of time at slow speed in order
to "seat" the brushes.
You're idea of seating the brushes is my idea of burning away the
carbon and spraying the debris all over the inside of the engine. Find
a round file with approximately the same diameter as the commutator
and file the brushes.
After a period of time you could tell that the
motor was not running as smoothly as it did at the beginning of the
test.
I'm not surprised that it was running rough with one brush burning,
the other not burning, and oily carbon debris everywhere.
Has anyone seen this before?
Not exactly the same but similar. I do Marklin trains. This should
give you a clue as to the Marklin motor issues, which might be similar
to yours.
http://stores.ebay.com/Eckerts-Marklin-Trains-and-Parts/Marklin-Motor-Repair-Parts.html
Is there a way to "arrest" the spark at the
brushes perhaps with capacitors?
Maybe. An RC series network would help. However, the values are
calculated for a specific rotation speed and would probably not work
well on a train motor with a wide speed range. I would concentrate on
finding out why this motor is different and why it's sparking. Save
the band-aids for later.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558