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[SOLVED] How to test field windings & armature windings of the DC motors ?

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munzir

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How to test field windings & armature windings of the DC motors ?

DMM shows very low resistance almost short (about 0.05 ohms) ... what to do ?


thanks
 

What is declared power of that motor? What type of motor ?

0,05R is very low resistance, high current will go.
 
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    munzir

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You could be reading the correct value depending on what sort of motor you are testing. A starter motor for a big car will take 200A at 10V while it is cranking the engine over. R = 10/200 = .05 ohm. What do you hope to find while testing it? A visual inspection will show if the commutator is burnt or the field coils have been over heated.
Frank
 
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    munzir

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How to test field windings & armature windings of the DC motors ?

DMM shows very low resistance almost short (about 0.05 ohms) ... what to do ?


thanks
 

How to test field windings & armature windings of the DC motors ?

DMM shows very low resistance almost short (about 0.05 ohms) ... what to do ?


thanks


I dont think that is smart to put that baby on some power supply :???: Or you can try on some batteries.
 

Few tips when you check the brushed dc-motor,

-disconnect all wires from motor

-turn motor slowly with hand and check is the rotor turning without jamming or stucking
....if so >> mechanical fail ... check bearings ...is field magnet loose...other loose parts.

Try to move the motor shaft axial and radial directions to find out is there right clearence in bearings.

-if motor has field winding(s) , look voltage and current values for field in name plate.
-calculate resistance and check by measuring

Usually brushed DC-motor has two, four or six brush holders.
-take away brushes so that only one pair is left in place in opposite sides ( difference 180 degrees )
-connect ohm-meter to armature wires and turn slowly rotor so that you can read ohm value for
every commutator plate pair. No higher resistance values are allowed.

Check every brush , no arc-marks , no grooves , equal lenght , not too short , copper conductor to brush is undamaged ,
if spring attached to brush , check that spring is undamaged and it makes enought pressure against commutator plates

Check brush-holders , brush must move freely in holder , check that brush size is suitable with holder.

If separate springs fo brushes are used , check pressure of the springs and test freely movement of springs

Check that all wires and contacts are in good condition

check the commutator plates surface condition
-no deep grooves
-no burned arc-marking
>> if arc-marks clearly occurs in one or two places , there could be armature coil failure
>> if arc-marks are random or all around , there is fail with brushes . ( low brush pressure , too short brush )

Test with low voltage adjustable power supply ( current limited or over current protected )

For motor with fixed magnet fied , connect supply and adjust voltage so that motor start slowly run. ( adjust current limit )
-check that motor run smoothly
-brake motor with hand , still should run smooth
-stop motor with hand and slowly let turn 360 degrees , no loss of torque allowed in any angle.
>> if point of torque-loss found , mark the position and check reason. ( fail in armature winding , commutator , brushes , brush-holders )

If motor has field winding connect mains isolated supply and adjust current 25...50% of name plate rating.
Do above tests

It is a great help in troubleshooting , if you know exact how the fault appeared and how the motor behaved in failed situation.

Good to remember, DC-motor commonly has tachometer included
and failed tacho can cause fault conditions ,
which could affect like fault on the motor.
So allways check the tachometer too.

There was some,
friends can tell additional tips...........
 
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