DC motor's spark grade have relationship with power lead?
DC motor's spark grade have relationship with power lead?
(OP)
Hi,
We meet a problem on a DC motor. We adjust the brush position OK by same speed at CW&CCW direction with non_load. But only one direction is OK if judged by spark and torque between brush and commutator bar with load on(15N.m/1000rpm). In aother direction the spark is very violent, also the motor cann't output 15N.m torque(the motor should output 15N.m/1000rpm at CCW&CW). The armature current is about 170A(4 poles,4 brush carbons). But if I exchange the power lead "+" & "-" which connected to the brush lead wire, the spark is changed also. That's to say, if brush 1,3 to '+' and brush 2,4 to '_", the CCW is OK and CW is very bad(violent spark and no 15N.m), when the brush 1,3 to '_' and brush 2,4 to '+', then CCW is very bad and CW is OK. We also adjust the brush position in CCW or CW the phenomenon still appears. We are not sure why this happens. Any advice about it will be very appreciate.
Thank you.
Boyd
We meet a problem on a DC motor. We adjust the brush position OK by same speed at CW&CCW direction with non_load. But only one direction is OK if judged by spark and torque between brush and commutator bar with load on(15N.m/1000rpm). In aother direction the spark is very violent, also the motor cann't output 15N.m torque(the motor should output 15N.m/1000rpm at CCW&CW). The armature current is about 170A(4 poles,4 brush carbons). But if I exchange the power lead "+" & "-" which connected to the brush lead wire, the spark is changed also. That's to say, if brush 1,3 to '+' and brush 2,4 to '_", the CCW is OK and CW is very bad(violent spark and no 15N.m), when the brush 1,3 to '_' and brush 2,4 to '+', then CCW is very bad and CW is OK. We also adjust the brush position in CCW or CW the phenomenon still appears. We are not sure why this happens. Any advice about it will be very appreciate.
Thank you.
Boyd





RE: DC motor's spark grade have relationship with power lead?
If the motor is compound wound, it is designed to operate in one direction only. That direction is the one which makes F1 and S1 both positive when running. For reverse rotation, only the A1 and A2 leads are reversed.
Running with the series field bucking the shunt field can cause the arcing problem you mention and certainly takes away a good share of the torque output.
RE: DC motor's spark grade have relationship with power lead?
Thank you. Sorry I donn't describe the motor clearly. This motor is separate field motor. Two shunt-wound of two series-wound of field pole windings are here. And pls see the enclosed file. I just exchange the A1 and A2 lead connected to power source.
RE: DC motor's spark grade have relationship with power lead?
RE: DC motor's spark grade have relationship with power lead?
Rocking the brush arms should correct most of the sparking, but limited the allowed range you can shift the arms. Shorts on the winding relocates the motor flux fields around and is usually the culprit.
Additional question: Did you change brush grades or changed the brush tensions? Basically, higher contact resistance on one/ two brushes of a four-brush arm will load up the other brushes resulting to sparking and lesser torque too.
Just trying to cover other gray areas.
RE: DC motor's spark grade have relationship with power lead?
Thank you. In fact I have try two rotors. I'll check the armature.
Burnt2x,
Yes. I have moved the four brush about 1Min-6Max degrees in CCW or CW direction but no effect. I'll check the tension again, also the brush.
Thank you.
RE: DC motor's spark grade have relationship with power lead?
Are the brushes a good fit into the holders i.e. not tilting in reverse.
Roy
RE: DC motor's spark grade have relationship with power lead?
Bill
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"Why not the best?"
Jimmy Carter
RE: DC motor's spark grade have relationship with power lead?
You can also check the armature for shorts with the motor fully assembled. Lift all the brushes & apply shunt field excitation only. Rotate the armature slowly by hand, if there is a short the armature will have a tendency to lock in one position.
RE: DC motor's spark grade have relationship with power lead?
You also see the interpoles in generators that never reverse.
RE: DC motor's spark grade have relationship with power lead?
Thanks very much to all of you. The cause have been found out finally and no problem in motor, but a unbelievable mistake in the test dynamometer. Much time on motor but finally not it, a lesson to me!
RE: DC motor's spark grade have relationship with power lead?
Thanks for the update and closure.
RE: DC motor's spark grade have relationship with power lead?
Roy
RE: DC motor's spark grade have relationship with power lead?
1. Dynamometer registered a lower torque when the motor was actually loaded beyond its rating. Overloaded DC motor gets more amps on each of the brushes which was indicated by the 'sparking'.
2. Degree at which the corrective action of interpoles (if any) wasn't enough to relocate the flux center.