DC Motor Problem

Have you checked for ball bearing condition on the motor shaft? It sounds to me like the shaft is pulling when the field comes on and then the armature cage rubs on the magnets.

It could also be that the magnets are loose due to glue failure.

The armature has been damaged, there are shortcuts in the windings. You have to have it rewinded.

Has the armature been removed and dropped? I like the answer about the bearing problem since the armature binds when the field is energized. That sounds like a reasonable solution

Dc motors with an external field don't have magnets. The armature voltage must have one IR (current * resistance) drop 20 volts DC for most motors before the armature will turn. Armature voltage at the terminals are dependent on speed of the rotor. The field fixed or variable creates the flux to produce the torque that is a result of load placed on the armature. So the terminal voltage of the armature is speed and the current through the armature leads are a result of the amount of load on the motor ( the Spindle). It is normal to have a fixed field voltage and the current is set for full field if you want the motor speed to go above base speed you actually weaken the field. This works within range of load as field weaking also produces less field flux and provides less torque in the motor.

You could have bearing in the motor or spindle giving problems you could have a grounded field either to case of motor or to armature. An SCR not firing can also reduce torque and allow motor to run under no load but would overload with a load applied.

There is a possibility of residual magnetism in the motor so applying the field you may notice some sticking while trying to turn by hand.

Au contraire. The field winding creates a magnetic field that repells/attracts the field generated in the armature windings. Do not believe that this is not a magnet, although an electromagnet.

Mr. Hooie

i like your comments,

today itest same motor with external field 220vac to full dridge i.e about 180vdc as a field. and start applying armeture field from 0vdc to 24 vdc current consumption for this is about 0 to 20 amps. ( before it runs 3000 RPM @ 24 vdc)

no any wiending are tuching to ground

field is consuming 1.5 to 2 Amps current.

Motor tameplate shows 1.4 A field current and armetur current 23.5 amps max

i dont feel any bearing jam condition

may armeture short

please add some comments

thanks.

jarunmagnet