Project - Analysis of a practical automotive wiring circuit

Question 1: Identify each of the major elements in the above automotive wiring diagram.

Answer: Following are the major elements in the automotive wiring harness diagram.

1. Battery
2. Starter
3. Ignition coil
4. Distributor
5. Breaker
6. Current and voltage regulator
7. Generator
8. Switch
9. Fuse
10. Horn
11. Lamp

Question 2: Explain the purpose and working of any three elements briefly.

Answer:

1. Battery:

A battery is a device that converts chemical energy into electricity. An automotive battery is wet cells type battery which contains Cathode, Anode and electrolyte material. The type of battery in gasoline and diesel internal combustion engines is SLI batteries which serving the purpose of starting, lighting, and ignition on vehicles.

Function on battery in automotive vehicle as below

1. The primary functions of battery in automotive engines are to power the starter motor so as to run the engine.
2. All electrical components in a vehicle rely on the battery.
3. In modern cars where most parts like the injector system, spark plug, sensors are also powered by the battery

The major components of batteries used in automotive engine engines as below

Container – Is a part made of the steel can, used to enclose the substances of the cell to form a cathode, which is a part of the electrochemical reaction.

Cathode – positive or oxidised electrode, gain electron from the external circuit. It is the electrode reduced by the electrochemical reaction.

Separators –fibrous fabric that separates the electrodes.

Anode – Negative or reducing electrode, release electrons to the external circuit

Electrolyte – is the medium for movement of ion within the cell. It carries the ionic current inside the battery.

Collector – is a brass pin in the middle of the cell that conducts electricity to the outside circuit.

In Automotive vehicle, Lead acid type battery is used. Batteries have six cells, containing two plates at each. One of the plates is made of lead and the other with lead dioxide. Each cell can produce about 2-volts of energy. The plates are submerged in Sulphur acid that allows the two plates to react. This acid will trigger a reaction on the lead dioxide plate causing it to create ions and lead sulphate.

The irons created by the lead dioxide plate react to the other plate to produce lead sulphate and hydrogen. This result in a chemical reaction that produces electrons, the electrons move around the plates and generate electricity. The electricity flows out through the terminals to start the car and power other electrical components of the car.

2. Current & Voltage Regulator:

A voltage regulator is an electronic device that regulates the voltage in an electrical circuit. It is used to maintain a constant voltage level in a circuit, regardless of changes in load or supply conditions.

There are two basic types of voltage regulators: linear and switching. Linear regulators work by maintaining a constant output voltage, regardless of changes in input voltage or load current.

Switching regulators work by converting the input voltage into a high-frequency AC signal, which is then converted back into the desired output voltage.

Voltage regulators are an essential component in many electronic devices and systems. Without a voltage regulator, the voltage in a circuit would fluctuate based on changes in load or supply conditions, which could cause damage to electronic components.

Car voltage regulators are responsible for maintaining a constant voltage level in the electrical system, regardless of changes in load or supply conditions.

The regulator consists of two main components: a rectifier and a regulator. The rectifier converts the AC into DC, and the regulator controls the amount of current that flows through the rectifier.

3. Generator:

Automobile generator - a unit that converts mechanical energy into electrical energy and performs the following functions:

1. provides a constant and continuous battery charge when the engine is running;
2. provides power to all systems during engine start, when the starter consumes a large amount of electricity.

The generator is installed in the engine compartment. Due to the brackets, it is attached to the engine block, driven by a drive belt from the crankshaft pulley. An electric generator is connected in an electrical circuit in parallel with the storage battery.

The battery is charged only when the generated electricity exceeds the battery voltage. The power of the generated current depends on the revolutions of the crankshaft, respectively, the voltage increases with the revolutions of the pulley with a geometric progression. To prevent overcharging, the generator is equipped with a voltage regulator that adjusts the amount of output voltage, providing 13.5-14.7V.

Need to Generator on automotive vehicle.

1. Recharge the battery;
2. Provide sufficient energy for each unit of the machine's electrical system;
3. In emergency mode or at maximum load, perform both functions - and feed the battery, and provide energy to the vehicle's electrical system.

The generator consists of:

1. body (front and back cover);
2. stator;
3. rotor;
4. diode bridge;
5. pulley;
6. brush assembly;
7. voltage regulator.

The generator works as follows: when the key is turned in the ignition lock, the mains is turned on. The voltage from the battery goes to the regulator, which in turn transfers it to the copper slip rings, the final consumer is the rotor excitation winding.

From the moment the engine crankshaft rotates, the rotor shaft begins to rotate through the belt drive, an electromagnetic field is created. The rotor generates an alternating current, when a certain speed is reached, the excitation winding is powered from the generator itself and not from the battery.

The alternating current then flows to the diode bridge. The voltage regulator monitors the operating mode of the rotor, if necessary, changes the voltage of the field winding. Thus, provided that the parts are in good condition, a stable current is supplied to the battery, providing the on-board network with the required voltage.

The battery indicator is displayed on the dashboard of more modern cars, which also indicates the status of the generator (it lights up when the belt breaks or reloads).

Question 3: If the total load is 10A from battery, what should be the fuse rating?

Answer: Fuse rating calculation:

A fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It’s a single function device, and historically single-use. Calculating the rating of very basic protection equipment fuse, we use the thump rule just select a fuse rated 150% - 200% of normal operating current of the specific circuit.

Here, Total load from battery i.e Current (I) = 10A,

So, fuse rating= 1.5 X total load from battery

Fuse rating = 1.5 X 10 A

Fuse Rating = 15 A

Question 4: If 500W is the load, what is the voltage and capacity of battery you recommend?

Answer:

Here, load (P) = 500 W,

Battery voltage (V) = 12V … (Given)

First, we find require current (I) from given data,

We know that, Power (P) = Voltage (V) X Current (I),

Hence, Current (I) = Power (P) / Voltage (V)

Current (I) = 500 (W) / 12 (V)

So, Current (I) = 41.6 Ampere

We know that Battery capacity is nothing but the amount of energy a battery can deliver in an single discharge. If is expressed in Ampere.Hours (Ah).

Now from given data, we calculated current (I) value as 41.6 Amperes.

So, Battery capacity = Current (I) X time (hours)

Battery capacity = 41.6 (Amperes) X 1 (Hours)

Hence, Battery Capacity = 41.6 Ah

Here, we consider as nearest battery capacity value as 45 Ah.

So, for 500W load, we recommend battery capacity as 45Ah for 12V voltage.

Question 5: Identify any two elements which are connected parallel to each other. Why they are connected in parallel?

Answer: From given automobile wiring diagram, Horn and Sealed Beam Headlights are connected in parallel.

This are connected in parallel because they need to function at a constant supply of voltage. This voltage can be supplied to each of the this only when they are connected in parallel. In a parallel circuit, there is no variation in the potential difference on each of the electrical devices connected. In other words, the potential difference across all of them remains the same.

Therefore, horn and sealed beam headlights are connected in parallel so that each of them receives an identical potential difference. Also, a parallel combination facilitates the operator to switch ON only those circuits that are needed by the operator. If one circuit fails in a parallel combination, it doesn’t affect other circuit.

Question 6: Identify any two elements which are connected in series. Why they are connected in series?

Answer: From given automobile wiring diagram, Fuse and Stop Light Switch are connected in parallel.

A series circuit is a closed circuit where the current follows one path. In a series circuit, the devices along the circuit loop are connected in a continuous row, so that if one device fails or is disconnected, the entire circuit is interrupted. Thus, all devices along the circuit stop working at the same time.

In this given circuit it is connected in series because in case of any overload current than rated current or short circuit in circuit, before that current going to the Stop light switch it will first flow through fuse. It ensures safety of circuit from short circuit.