with dmm what should be the first tests? motor is in a difficult location to examine visually so i'd like to start with electrical evaluation.
it measures 1.2 ohms between the 2 armature leads.
thanks.
Do you have another reference motor to test against?
Check the inductance Check dielectric breakdown to earth Apply short voltage pulse, and check the ringing voltage with a scope (never done this, but perhaps you can get it to move just a quarter rotation and when you let go again the relaxation of the axis will produce a EMF voltage back, that you can monitor)
Apply DC voltage, take cover..
Cheers
Klaus
Paul Conners prodded the keyboard with:
If it isn't turning, then check that it has actually got voltage applied to it. You have to consider both the motor and controller !
--
Best Regards:
Baron.
Can you spin the shaft and see how much voltage it generates?
Ohm it to ground, too.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Perhaps if we knew in what way the motor was acting up we could better suggest a course of diagnostics. Like does it make any noise, does it turn slowly or not at all, is it popping the breaker, etc.
The faq,
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.
Michael
Not likely that his info is pertinent for 180 volt motors of that size, when his info is for miniature DC motors.
The motor types likely differ as well.
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 contact.
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.
Jamie
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?
Thanks.
Open it up and see if it has discolored windings. Does it smell burned? It would seem to me that the resistance readings indicate compromised winding insulation.
ng
re
p to
I have no expertise so can't answer on what is normal. But I am pretty sur e the resistance ought to be uniform. So sounds like the armature needs to be turned or at least have the surface cleaned. The 2.3 ohm reading might indicate a short in the armature.
But DC motors will work at voltages much lower than the name plate voltage. I would probably just connect a 12 volt supply to it and see if it turns sl owly.
Dan
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