205C - Cranking Systems Fundamentals and Motor Drive

Question 1

At what approximate speed does a starter rotate the engine at?

Answer 1

About 250 rpm

205c pg. 2

Question 2

What is the approximate gear ratio between the flywheel and starter pinion gear?

Answer 2

20:1

205c pg. 2

Question 3

What is the maximum time that an engine starter should be cranked for?

Answer 3

30 seconds, 2 minutes cool-down

205c pg. 6

Question 4

What do some manufacturers do to ensure voltage drops between the batteries and starter are kept to a minimum?

Answer 4

Use two positive cables in parallel and two negative cables in parallel.

205c pg. 4

Question 5

What determines the required engine starter circuit cable gauge size?

Answer 5

• The distance between batteries and starter
• Current required for cranking

205c pg. 4

Question 6

Starting with the operator pressing the start button, what is the order of events in the starter control circuit?

Answer 6

Engagement:
- Operator presses start button
- Starter relay pull-in & hold-in windings are energized (In parallel)
- Starter solenoid meshes drive pinion with flywheel & closes solenoid switch contacts BAT & M

Engaged:
- Battery current flows from BAT to M terminals to turn starter motor
- Pull-in windings de-energize
- Hold-in windings remain energized

Release:
- When engine starts, operator releasing start button stopping current flow to S terminal
- Battery current flows from M to S terminal through pull-in windings, then through hold-in windings to G terminal
- Opposing polarity of solenoid windings in series cancels magnetic field, releasing the plunger
- Return spring in the solenoid pulls contacts disk off BAT & M terminals and acts on shift lever to disengage pinion gear from flywheel
- Brake washer slows armature rotation to a stop.

205c pg. 8

Question 7

What is the main rotating component in a starter?

Answer 7

The armature assembly

205c pg. 10

Question 8

What are the two main electrical components mounted to the armature shaft?

Answer 8

• Armature windings
• Commutator

205c pg. 10

Question 9

What are alternator armature windings made of?

Answer 9

Heavy flat copper strips that have low resistance.

205c pg. 10

Question 10

How is the starter armature designed to help reduce eddy currents?

Answer 10

Laminated core

205c pg. 10

Question 11

Do alternators have even or odd combinations of brushes?

Answer 11

Even, that match the number of field windings and pole shoes.

205c pg. 11

Question 12

If a cranking motor has six field windings and six pole shoes, how many brushes will it have?

Answer 12

Six.
Even number of brushes. Same number of brushes as field windings and pole shoes.

205c pg. 11

Question 13

What material are most starter motor brushes made of?

Answer 13

Mixture of copper and carbon.
- Copper is good conductor
- Carbon provides dry lubrication

205c pg. 11

Question 14

Starter motors contain two magnetic fields. Where are they? Do they repel or attract each other?

Answer 14

Field windings:
- Stationary, concentrated by the pole shoes

Armature Windings:
- Armature rotates in the starter

Magnetic lines of force are parallel to each other and repel.

205c pg. 12

Question 15

What form of energy is a byproduct of starters converting electrical energy into rotational mechanical energy?

Answer 15

Heat energy

205c pg. 13

Question 16

In a starter motor, are the armature windings and field windings connected in series or parallel?

Answer 16

Series

205c pg. 14

Question 17

What will limit the top speed of an unloaded, bench operated (free running) cranking motor?

Answer 17

CEMF - Counter electromotive force

205c pg. 15

Question 18

When a series connected cranking motor is rotating slowly, the CEMF value is ______ (high/low) and the current draw is ______ (high/low).

Answer 18

At slow rotation speeds:
- CEMF is low
- Current draw is at its highest

205c pg. 16

Question 19

In a series connected cranking motor, current draw will ______ (increase/decrease) as the speed of the armature increases?

Answer 19

Current draw will decrease as armature speed increases

205c pg. 16

Question 20

Does a starter motor with series or parallel wound field coils generate more torque?

Answer 20

More torque from a parallel wound field coil

205c pg. 17

Question 21

Which type of starter motor field winding configuration has all of the current flowing through each coil?

Answer 21

Series wound

205c pg. 16

Question 22

Which type of starter motor field winding configuration has current flowing equally between all field coils?

Answer 22

Parallel wound

205c pg. 17

Question 23

Which type of starter motor field winding configuration has the current split between two pairs of field coils?

Answer 23

Series-Parallel wound

205c pg. 18

Question 24

What are compound wound (shunt) starter motor field winding configurations designed to prevent?

Answer 24

Prevents destructive overspeed conditions.

205c pg. 18

Question 25

How does a compound wound starter motor field winding configuration prevent overspeed conditions?

Answer 25

A shunt winding is wired in parallel to the regular series wound field coils and is grounded to the motor frame. This shunt produces a constant high magnetic field that creates a speed limiting CEMF. 205c pg. 19

Question 26

What two components provide the starter motor’s stationary magnetic field?

Answer 26

- Pole shoes - Field windings 205c pg. 21

Question 27

How are starter motor pole shoes properly oriented?

Answer 27

With the longer, leading edge, positioned in the direction of armature rotation. 205c pg. 21

Question 28

How are starter motor field windings securely held in place inside the starter?

Answer 28

Held in place by the pole shoes 205c pg. 22

Question 29

Are starter motor field coils and armature windings connected in parallel or series with each other?

Answer 29

Series 205c pg. 22

Question 30

What materials are used as electrical insulating material in the cranking motor?

Answer 30

- Varnish coatings - Bakelite - Mica

Question 31

In a four pole cranking motor with four brushes, what do the brushes connect to?

Answer 31

- Two brushes are grounded and wear on the commutator - Two insulated brushes connect to the field coils and wear on the commutator 205c pg. 23

Question 32

What material and type of bearing is used to hold the rotating armature shaft?

Answer 32

Sintered brass bushings 205c pg. 24

Question 33

How many bushings do heavy duty cranking motors have?

Answer 33

Three - 1 in brush holder housing - 2 in drive end housing/nose housing 205c pg. 24

Question 34

What is the purpose of the brake washer in a cranking motor?

Answer 34

Located between the movable drive mechanism and a stationary member of the cranking motor. Purpose is to slow down and stop the armature assembly after the engine has started and the drive mechanism is disengaged. 205c pg. 25

Question 35

What is a cranking motor overrunning clutch used for?

Answer 35

Prevents the engine from spinning the armature immediately after it’s been started. Uses rollers. 205c pg. 27

Question 36

What is the role of a sprag clutch in a cranking motor?

Answer 36

Prevents the cranking motor armature from being driven by engine flywheel after the engine starts, resulting in overspeed damage. Uses banana shaped locking elements instead of rollers used in the overrunning clutch. 205c pg. 28

Question 37

What are cranking motor pinion drive teeth manufactured with to reduce the likelihood of a tooth on tooth abutment during drive engagement?

Answer 37

A chamfered edge 205c pg. 28

Question 38

What is the role of the meshing spring in a cranking motor?

Answer 38

If the pinion gear teeth butt into the flywheel teeth and do not mesh, the spring will compress and accommodate the shift lever’s full travel so that the solenoid switch will close and begin turning the armature. Once the armature begins to turn, the mesh spring and pinion gear chamfer allow the gear to mesh with the flywheel. This prevents damage by operating with partial tooth engagement. 205c pg. 28

Question 39

In a cranking motor armature, where are opens most likely to occur?

Answer 39

At the armature winding connection to the commutator riser bar. Due to excessive heat, the soldered connection may separate and create an open. 205C pg. 22