Page 215 - Electrician - TT (Volume 1)
P. 215
ELECTRICIAN - CITS
Chart 1
Troubleshooting chart for DC motors
Symptoms Cause Remedies
Motor will not start a) Open circuit in starter. a) Check for open starting
resistor,
b) Low or no terminal voltage. b) Check the incoming voltage
with name-plate rating and
correct the supply voltage.
c) Bearing frozen. c) Recondition the shaft and
replace the bearing.
d) Overload. d) Reduce the load.
e) Excessive friction. e) Check the bearing lubrication to
make sure that the oil is sufficient
quantity and of good quality.
Disconnect motor from driven
machine and turn motor by hand
to see if trouble is in motor.
Strip and reassemble motor; then
check part by part for proper
location and fit. Straighten
or replace bent Shaft.
Motor stops after running a) Motor is not getting power. a) Check voltage in the motor
short time terminals: also fuses and
overload relay. Rectify the defect.
b) Motor is started with weak or no b) If adjustable-speed motor, check
field.the rheostat for correct
If correct, check the condition of
rheostat. Check the field coils for
open winding. Check the wiring
for loose or broken condition
c) Motor torque insufficient to drive c) Check the line voltage with name
load. plate rating. Use larger
motor or one with suitable
characteristic to match the load.
Motor runs too slow a) Line voltage too low. a) Rectify the supply voltage or
under load. under load check and remove any
excess resistance in supply line,
connections or controller.
b) Brushes ahead of neutral plane. b) Set brushes on neutral plane.
c) Overload. c) Check to see that load does not
exceed allowable load on motor.
Motor runs too fast a) Weak field. a) Check for resistance in shunt-
under load. under load field circuits.
Check for grounds.
b) Line voltage too high. b) Correct high voltage condition.
c) Brushes are out of neutral plane. c) Set brushes on neutral plane.
202
CITS : Power - Electrician & Wireman - Lesson 30-37
