How to troubleshoot dc motor

How to troubleshoot dc motor?

How to troubleshoot dc motor? Common Faults And Treatment In DC Motor Operation

1, DC motor can not start after the power is applied

DC motor start necessary enough starting torque (to be greater than the starting static resistance torque), and to provide starting torque necessary two basic conditions, one is to have sufficient electromagnetic field, the second is to have sufficient armature current. For its failure to start should also be the core of the detection, analysis, testing.

Failure causes
(1) armature circuit break, no armature current, so no starting torque, can not start. Fault points are mostly in the armature circuit control switch, protection appliances, and armature coil and commutation pole, compensation pole joints.
(2) excitation circuit break; excitation resistance is too large; excitation line grounding; excitation winding repair after the air gap increases. These magnetic field faults will cause lack of magnetism, weakened magnetic field, so no starting torque or starting torque is too small to start.

(3) The starting load torque is too large, and the electromagnetic torque at starting is less than the static resistance torque.
(4) Short circuit between turns of armature winding, insufficient starting torque.
(5) Brush is seriously misaligned.
(6) Poorly ground brushes and excessive pressure.
(7) Motor load.

Handling method
(1) For armature disconnection and excitation circuit disconnection, find the disconnection point along the two circuits respectively, replace the faulty switch and repair the disconnection point.
(2) Find the short circuit point and repair or replace it partially.
(3) For armature starting resistance, excitation starting resistance readjustment (armature resistance adjusted to large, excitation resistance adjusted to small)
(4) Adjust brush position to geometric center line, fine grinding brush, test and adjust brush pressure to correct value. (5) For desoldering points should be re-welded.
(6) If the load is too heavy, the load should be reduced to start.

2, The armature smoke

Mainly by the armature current current is too large, armature winding insulation heating damage

Failure causes
(1) long period of overload operation.
(2) commutator or armature short circuit.
(3) generator load short-center.
(4) Motor end voltage is too low.
(5) Motor direct starting or reverse running frequently.
(6) The stator and rotor cores rub each other.

Handling method
(1) restore the normal load.
(2) Use millivolt meter to detect whether there is short circuit, whether there are metal chips falling into commutator or armature winding.
(3) check whether the load line is short-circuited.
(4) restore the normal value of voltage.
(5) Avoid frequent and repeated operation.
(6) check whether the electrical gap is uniform, whether the bearing is worn.

3, The DC motor temperature is too high

The increase in temperature is the result of increased losses, mainly electromagnetic losses and mechanical losses.

Failure causes
(1) the power supply voltage is too high or too low.
(2) Excitation current is too large or too small.
(3) short circuit between turns of the armature winding.
(4) excitation winding inter-turn short circuit.
(5) air gap eccentricity.
(6) short circuit in the iron core.
(7) stator and rotor cores rubbing against each other.
(8) poor ventilation channel; poor heat dissipation.

Handling method
(1) adjust the power supply voltage to the standard value.
(2) find the cause of excitation current too or too small, the corresponding treatment.
(3) find the short circuit point, local repair, or replace the winding.
(4) adjust the air gap.
(5) repair or replace the core.
(6) correct the shaft and replace the bearings.
(7) dredge the air duct, improve the working environment.

4, The brush under the spark is too large

There are mainly electromagnetic reasons, mechanical, electrochemical, maintenance and other reasons can not be ignored.

Failure causes
(1) the brush is not on the center line.
(2) brush and commutator for poor contact.
(3) Loose brush grip or incorrect device.
(4) brush and brush grip with too tight.
(5) the brush pressure size is improper or uneven.
(6) commutator surface is not polished, not round or dirt.

(7) Mica protruding between commutation plates.
(8) Excessive brush wear.
(9) saturation of commutation pole or violent fluctuation of load during overload.
(10) short circuit of commutation pole winding.
(11) Overheating of armature, desoldering of joint piece of armature winding and commutator.
(12) reversal of the commutator winding during overhaul.
(13) Uneven brush holder position, resulting in uneven current distribution between brushes; uncorrected rotor balance.

Handling method
(1) adjust the position of the brush holder.
(2) Grind the brush contact surface and run under light load for half an hour.
(3) Tighten or correct the brush grip position.
(4) Adjust the brush grip spring pressure or change the brush grip.
(5) Clean or grind commutator surfaces.
(6) Commutator grooving, chamfering, regrinding.
(7) Replace the brush according to the original brand of the manufacturer.

(8) restore the normal load.
(9) tighten the foot bolt to prevent vibration.
(10) Check the commutation pole winding and repair the damaged insulation layer.
(11) check the commutation piece desoldering, repair.
(12) Check the polarity of the main pole and commutation pole with compass, and correct the wiring.
(13) adjust the position of the brush holder, equal evenly.
(14) re-calibrate the rotor dynamic balance.

5,Housing leakage

The surface insulation level is lowered, the short circuit in the armature and excitation line exists.

Failure causes
(1) harsh operating environment, the motor is damp, insulation resistance reduced.
(2) power lead connector touching the shell.
(3) out of the plate, winding insulation damage.
(4) grounding device a good.

Handling method
(1) measure the insulation of the winding to the ground, such as below 0.5 M, should be dried.
(2) re-wrap the joint, repair the insulation.
(3) detect the grounding electric yin is in line with the provisions of the standard grounding.


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