Deck 8: DC Motors

Question 1

A growler is used to test for shorted pole shoes.

Answer 1

False

Question 2

A technician measures approximately 0Ω of resistance between each commutator segment. This indicates a shorted to ground armature loop.

Answer 2

False

Question 3

The cable between the battery positive terminal and the starter motor is typically protected by a 500A MEGA fuse.

Answer 3

False

Question 4

Starter motors can be safely operated for two minute intervals, provided a 30 second period between crank attempts to permit the motor to cool is observed.

Question 5

A loss of residual magnetism of the pole shoes can cause the starter motor to not operate.

Question 6

Cranking circuit resistance can be accurately measured by a DMM ohmmeter, provided the meter test lead resistance is zeroed out first.

Question 7

A gear reduction starter motor is typically much larger and heavier than a comparable direct-drive starter motor.

Question 8

Referring to the figure shown below, an open circuit between the magnetic switch output terminal and the cranking motor solenoid would likely cause the magnetic switch to "click"
when the ignition switch is in the start (crank) position but the engine would not crank.

Question 9

The reason that an electric motor draws less current as motor speed increases is the result of____?

A) the negative temperature coefficient of copper
B) series-aiding voltage sources
C) counter-electromagnetic force (CEMF)
D) Kirchhoff's current law

Question 10

Technician A says that a starter motor which draws excessive current and has low cranking speed could be caused by an internal engine problem. Technician B says that excessive cranking circuit resistance can cause low cranking speeds. Who is correct?

A) A only
B) B only
C) Both A and B
D) Neither A nor B

Question 11

The ______ and ______ provide electrical contact with the armature loops.

A) Bendix, field
B) commutator segments, brushes
C) pole shoes, brushes
D) windings, shunt

Question 12

Technician A says that a charging system problem could cause low cranking speeds. Technician B says that the wrong viscosity of engine oil could cause low cranking speeds. Who is correct?

A) A only
B) B only
C) Both A and B
D) Neither A nor B

Question 13

Which component is typically not found in a heavy-duty truck starter motor?

A) Brushes
B) Armature
C) Permanent magnet
D) Field coil

Question 14

Technician A says that diesel engine that will not crank could be caused by a loose primary fuel filter permitting air to be drawn into the fuel. Technician B says that a diesel engine that will not start in extreme cold weather could be caused by low cetane fuel. Who is correct?

A) A only
B) B only
C) Both A and B
D) Neither A nor B

Question 15

Which of the following is a true statement?

A) A permanent magnet DC motor typically would not have brushes.
B) Most heavy-duty truck starter motors are series-wound motors.
C) The pole shoes in a DC motor are attached to the armature.
D) All of the above are true statements.

Question 16

Referring to the following figure, a medium-duty truck with an automatic transmission is reported to not crank. Which of these steps should be performed first to troubleshoot the cause?

A) Connect booster batteries and attempt to jump-start.
B) Check for loose electrical connections.
C) Verify the concern; attempt to crank the engine.
D) Jumper the neutral start switch since they typically fail.

Question 17

Referring to the figure shown below, technician A says that a shorted to ground circuit between the magnetic switch coil low side and the neutral start switch should cause the circuit protection device which protects the ignition switch circuit (not shown) to open and prevent the engine from cranking. Technician B says that a magnetic switch with stuck (welded) contacts will cause the cranking motor to operate with the ignition switch in the OFF position. Who is correct?

A) A only
B) B only
C) Both A and B
D) Neither A nor B

Question 18

A passenger side power window motor operates in one direction but not the other direction. Which is the most likely cause of this complaint?

A) Defective master (operators door) power window switch
B) Defective passenger power window switch
C) Worn brushes
D) Both A and B

Question 19

The ____ gear is driven by the starter motor armature shaft; the ___ gear drives the engine crankshaft when the starter motor is operating.

A) Bendix, flywheel
B) pinion, ring
C) commutator, flex plate
D) over running clutch, sprag

Question 20

Two magnetic fields that interact with each other combine to form a single magnetic field. If the arrows on the magnetic lines of force of both magnetic fields are pointing in the same direction, the resulting magnetic field is ____. If the arrows on the magnetic lines of force are pointing in opposite directions, the resulting magnetic field is ____.

A) strengthened, weakened
B) canceled out, intensified
C) unchanged, unchanged
D) forward biased, reverse biased