DC MOTOR

What is your question?

Firstly, are you talking about permanent magnet motors or field wound?

Field wound.

Remember, a good DC motor will hardly spark, even under varying loads as extra poles have been added, in series with the commutator, to correct the position of the magnetic lines of force so that the commutation happens only at the optimum position for NO sparking.

Sadly many cheap DC motors (and permanent magnet) do not have this correction and as spark free commutation will only then occur at one point of the load graph, any other point will bring sparking to a greater or lesser degree.....

Any DC motor, driven as a generator, will never produce a good output as the brushes will not be in the optimum position for a Generator, eg. voltage pickup as of course it was designed as a motor!

Though with an old fashioned motor where the brush position can be varied to a degree, it may be possible, while observing the sparking at the brushes, to find an optimum position where sparking is minimized or eliminated.

I must add, that I have never actually done this, it is more of a theoretical possibility, than a practical one!!!

The following is a quick illustration of some of the possible internal construction of DC field motors:-

this is from the following web site, goto

http://www.tpub.com/content/doe/h1011v2/css/h1011v2_112.htm

for more details if you wish.....

Permanent magnet motors are a further similar ball game!!!

from figure 1 i assume that you are asking about brush 2 of the DC machine making approx. 20 % contact with the commutator segments.

then it is possible that there will be significant arcing if the air gap is small and the DC input voltage high.

the latter might not be true if the armature is wave connected.

there is a significant difference between lap and wave connected armatures.

need more help let me know more

best of luck

You did not even show the direction of rotation, nor did you ask a question......

Have we supplied you with enough info? If not, then we need more info from YOU!!

Actually got 8 Dc Motors connected in 4 perallel line series of 2 motors.got over currect on one line. Please advice how to proceed to rectify the problem.

You are not giving us full information every time, why? Answer as a start the following questions please, then we might be able to go further.....might!!

Is the problem on a commutator or a field line?

Is the drawing correct, you have also series field coils with the commutator?

Why are you using separate supplies?

What are the voltages of the supplies?

Have you measured a good line amps?

What is normal?

What is the bad line amps?

Actually these 8 motors drive the ship to shore crane on the gantry rails to move left/right. These motor are identical in characteristic, 230V/86A armature, 120V/1.5A field. The VSD supply 460V to armature, 240V/12A (fix V & I) to field.

Got overcurrent on one armature line.

Task done:All 8 motors have been inspected: carbob brush, commutator cleaning, field resistance check-OK, field current per line check-All 4 line-OK, all 8 motors are in neutral position.

Please advice how to rectify overcurrent problem.

I have looked at the diagram and there would appear to be a major failure in the diagram you made which was:-

I feel that the diagram should be drawn as here:-

Please check and let us know which diagram is fully correct. If neither, please give us a fully corrected schematic asap.