205A - Charging System & Control Circuit Fundamentals

Question 1

What are the two main purposes of the charging system?

Answer 1

• Recharge the battery
• Power the electrical components on the unit

205A pg. 3

Question 2

What are four main characteristics of an alternator?

Answer 2

• Lightweight
• Can be operated at high speeds
• Can supply high current at low engine speeds
• Can operate in either direction providing the correct cooling fan is used

205A pg. 3

Question 3

What is the open circuit voltage (OCV) of a fully charged 12V battery?

Answer 3

12.6V

205A pg. 4

Question 4

What is the OCV of a fully charged 24V system?

Answer 4

25.2V

205A pg. 4

Question 5

How does an alternator regulator control the alternator output power?

Answer 5

By adjusting the rotor coil field strength.

205A pg. 5

Question 6

What is the maximum charging voltage of a 24V system?

Answer 6

29.6V

205A pg. 6

Question 7

What is the maximum charging voltage of a 12V system?

Answer 7

14.8V

205A pg. 6

Question 8

What are the two major circuits in a charging system?

Answer 8

• Field circuit (energizing the rotor coil)
• Output circuit (the high current output)

205A pg. 7

Question 9

An alternator induces a voltage by rotating ______ inside a ______.

Answer 9

Rotating a magnetic field (rotor) inside a fixed conductor (stator).

205A pg. 7

Question 10

At what rotor magnetic field angle is the greatest voltage induced into an alternator stator?

Answer 10

At right angles

205A pg. 7

Question 11

In an alternator, the constant change of voltage as the rotor and field rotate, creates what type of wave?

Answer 11

Sine wave

205A pg. 8

Question 12

For AC current to be usable in a DC system, it must be ______.

Answer 12

Rectified

205A pg. 8

Question 13

What is a rectifier bridge composed of?

Answer 13

• Six diodes: 3 positive bias, 3 negative bias
• Heat sink

Question 14

How is the electrical connection maintained to the rotor as it rotates?

Answer 14

Brushes that ride on slip rings

205A pg. 9

Question 15

What do alternators use to prevent heat from melting insulating material?

Answer 15

• Heat sinks
• Cooling fan

205A pg. 9

Question 16

What direction does air normally flow through an alternator?

Answer 16

From the rear to front

205A pg. 10

Question 17

What component is primarily responsible for limiting the maximum current output of an alternator?

Answer 17

Stator design. Due to inductive reactance.

205A pg. 11

Question 18

Why do alternators use a soft iron rotor core?

Answer 18

High permeability which provides a strong localized magnetic field

205A pg. 12

Question 19

Alternator rotors use a coil of insulated wire positioned between two pole pieces which localize the magnetic field. What range of pole combinations do heavy equipment alternators use?

Answer 19

From 8-16

205A pg. 13

Question 20

Is AC or DC current used to energize an alternator field?

Answer 20

DC
Typically 2-10 amps

205A pg. 14

Question 21

An alternator stator is made up of ______ conductors (windings) that are wound onto a cylindrical, insulated, _______iron core.

Answer 21

Made up of three windings.
Wound onto a laminated core.

205A pg. 15

Question 22

Why are stator cores laminated?

Answer 22

Reduce eddy currents which produce unwanted heat.

205A pg. 15

Question 23

What element of an alternator design results in the production of three-phase current?

Answer 23

Three windings in the stator

205A pg. 16

Question 24

What are the two types of stator winding configurations?

Answer 24

• Wye (Y)
• Delta

205A pg. 17

Question 25

How are the delta type stator windings in an alternator configured?

Answer 25

Three windings connected end to end.

205A pg. 18

Question 26

How are the wye type stator windings in an alternator configured?

Answer 26

One end of each winding connected at the stator junction

205A pg. 17

Question 27

What is it called, when all the available AC current in an alternator has been rectified?

Answer 27

Full wave rectification

205A pg. 21

Question 28

What material are alternator housings made of?

Answer 28

Aluminum

205A pg. 22

Question 29

How is an alternator stator mounted?

Answer 29

Firmly mounted between the front housing and rear housing/slip ring end housing.

205A pg. 22

Question 30

What is the role of a capacitor across an alternators positive diode output and ground?

Answer 30

• Potect alternator electronic components from transient voltage spikes
• Reduces radio frequency interference.

205A pg. 24

Question 31

How many ac rectifying diodes does an alternator with three stator windings have?

Answer 31

Six

205A pg. 25

Question 32

Alternators that are required to produce high voltage at low alternator speeds will use what type of stator winding configuration?

Answer 32

Wye type

205A pg. 26

Question 33

Alternators that require high current outputs use what type of stator configuration?

Answer 33

Delta type

205A pg. 28

Question 34

Each of the rotor north-south pole pairs produces ____ complete voltage sine wave per rotor revolution, across each of the three-stator windings.

Answer 34

One

205A pg. 28

Question 35

Once the alternator has started to produce current, rotor field current can be drawn from ______.

Answer 35

The alternator’s rectified current output - Diode trio

205A pg. 30

Question 36

What is a diode trio used for in an alternator?

Answer 36

Used in some alternators to rectify the ac current output to then power the rotor windings.

205A pg. 30

Question 37

How does inductive reactance limit the maximum output of an alternator stator?

Answer 37

The collapsing and building magnetic fields result in a self-induced voltage that opposes normal current flow, limiting the maximum output.

205A pg. 31

Question 38

What material are alternator brushes made of?

Answer 38

Carbon brushes in contact with copper slip rings.

205A pg. 32

Question 39

How does a voltage regulator control the alternator maximum output voltage produced?

Answer 39

By turning the field circuit on and off at appropriate intervals.

205A pg. 34

Question 40

Alternators are designed with two different types of field circuits in relation to the voltage regulator. What are they?

Answer 40

• A circuit
• B circuit

205A pg. 34

Question 41

How does an alternator field A circuit differ from a B circuit?

Answer 41

A circuit: Voltage regulator processes the current flow after the rotor windings. Regulator is positioned on the ground side of the windings.

B circuit: Voltage regulator processes the current flow before the rotor windings. The windings are on the ground side.

205A pg. 34

Question 42

Air enters an alternator from the ____ and is expelled out the _______.

Answer 42

Enters from the rear. Expelled out the drive end housing (front).

205A pg. 36

Question 43

What terminals do some alternators have that can be used to operate a tachometer, hour meter, or relay?

Answer 43

R or STA terminals
Provides a pulsing 14V DC signal which registers as 7V DC on a multimeter.

205A pg. 40

Question 44

In addition to operating a tachometer, hour meter, or relay, what else can the R or STA terminal be used for on an alternator?

Answer 44

To energize the rotor’s field coil if the residual magnetism in the pole pieces has weakened.

205A pg. 41

Question 45

How does a charging system indicator light operate?

Answer 45

Connected in parallel with a resister so field current will still flow if the bulb has an electric open.

Wired in series with the field circuit to one side. Battery voltage is supplied to the other side. When these two voltages are equal, there will be no voltage drop and the bulb will not illuminate. When the field circuit is not working properly and is not energized, there will be a voltage drop across the bulb and it will illuminate.

205A pg. 45