The faq, http://www.repairfaq.org has some words about the testing of DC
motors, though I'm not sure where.
I think Sam did write something about checking CD player motors, and I'm
sure he gave tips on figuring out whether it was good or bad.
those kind of motors tend to have mechanical issues..
Bearings is common which causes a tight turning shaft
and may cause the armature to move around on the brushes.
Also, a bearing could be completely blown out and the motor
will still make attempts to turn if the brushes are still making
Another issue is the PM's some times fall off, lose their bond to
the outer shell and come in contact with the rotor.
Then you get the occasion of weak magnets due from too many hours of
running hot, which causes more Arm current and lack of torque but with
higher RPM abilities.
Now and then, the armature windings may short to each other but not to
ground. Most of the time megger meters will not reveal this defect but
usually signs of over heated wire is a good bet.
Also, if you manually spin the motor it can act as a generator..
Disconnect the leads to the motor and see if it turns freely, if so then
you most likely do not have mechanical issue.. Now connect the ARM leads
together from the motor and see if you get heavy drag (Dynamic Braking)
due to energy being generated and short via the A1 and A2 leads. If you
do get a got drag on it, chances are it's of.
When checking the brushes via the DMM, you need to turn the motor very
slowly so that you can account for all the armature bars, you may have a
set of scorched brushes.
Motor out of the equipment. Turning armature slowly, the resistance reading
between the armature leads varies from a low of 2.3 to high of 10; most are
around 6-7 ohms. Resistance of each lead to motor frame is minimum 150K up to
over 1 meg.
What's normal for such a motor?
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