Project - Analysis of a practical automotive wiring circuit

The shown schematic diagram is of Automitive Wiring Diagram and the major elements are mentioned below:

- Battery

- Generator

- Starter

- Ignition System (Ignition Swith, Ignition Coil, Braker)

- Ammeter

- Fuse

- Current and Voltage Ragulator

- Switches (Light Switch, Ignition Switch, Horn Button, Foot Selector Switch)

- Accessories (Horn, Scaled Beam)

- Lights (Parking Lamp, PlaTC Light, DDMC light, Tail light)

- Earthing (Chassis Ground)

• Battery

Battery is an energy storage system. Basically, battery stores energy in form of chemical energy and converts it to the electric energy when circuit is completed. In foreign contries, there is one concept V2G (Vehicle to Grid) and G2V (Grid to Vehicle). In this, power coming from Grid has been strored in Vehicle's heavy duty battery. This concept solves two issues:

1> If electric connection is cut anyhow, energy stored in the battery can be used for various purposes.

2> If energy has been stored at when the electricity charges are cheaper, then that stored can be send back or sell back when the rate of electricity is higher. In some countries, electricity rates differ at different daytime. This can be very useful to get power or get profit. 

Battery cell consists of an Anode, a Cathode and an Electrolyte. As per the type of cell/battery, chemistry can differ.  When terminals are connected across an electric load, an electric current flows through it. Anode and Cathode are said to be electrodes in general terms.

In case of discharging, Anode is a Reducing Electrode as it releases electrode from it to the External Circuit. On other side, Cathode is a oxidizing electrode as it absorb the electrons from the external circuit and has. To complete the whole loop, absorbed electrons by cathode, flows through the electrolyte. Electrolyte facilitates the transfer of ions between the Anode and Cathode. 

Basically, Mordern batteries are made up of number of cells connected in series and parallel connection as per the optput required.  By connecting cells in series and parrallel, we can make batteries of diferent different capacity. To increase overall voltage of battery, cells should be in series and for overall current capacity, cells should be in parallel.

There are two types of cells: Primary, which can't be charged again and Secondary, which can be charged again till finite number of  recharge cycle. Depending upon function to be served, battery type can be chosen. 

• Ammeter

Ammete is an instrument to measure the current flowing through the circuit, whether it is AC or DC. Ammeter is used to monitor, measure and investigate the value of current flowing in the system continously. By this, we can be assured that the system or device is working ideally or not in terms of electric current.

To understand the working of an Ammeter, the behaviour of cuurent in parallel and series connection has to be understood first. Current to be indicated accurately, the resisance of an Ammeter,as a device, should be ZERO ohm ideally. But this case is not possible anyhow. So engineers trys to keep it as minimum as possible.

An ammeter needs to be connected in series and by having less value of resistance, it doesn't change the current from the circuit. The reason behind being in series in circuit is to get same valued current that device draws from the power input (AC or DC) and to indicate that value through coil deflection.

When the Galvanometer is connected to the Shunt Resistance having quite low value, this system behaves like an Ammeter. 

Types of Ammeter:

- Permanent Magnet Moving Coil (PMMC) (For DC only)

- Moving Iron (For AC & DC both)

- Electrodynamometer (For AC & DC both)

- Hot wire & Thermocouple (For AC & DC both)

- Rectifier type Ammeter (For AC & DC both)

- Digital Ammeter (For AC & DC both)

• Fuse

With each and every flow of the current, there is always losses associated depending upon the nature and working of devices. One of the major and always occuring loss is Copper Loss (Resistive Loss). This loss results in heating of the conductor. 

Fuse is made up of the thin wire of the alloy of tin and lead, which is having less melting temperature. According to the difference in diameter of the wire, it can have the different capacity of current passing through it. Beyond that level of the current, that thin wire reaches to its melting point due to the copper loss.

Basically, the purpose of the fuse is to protect the circuit and devices from the higher valued current which mostly happens in the case of the Short Circuit or over curent.

When short circuit happens in the live circuit, the value of current increases suddenly at higher value and it can cuase damage to the device connected in the circuit. But if fuse is connected in series to the whole circuit, it can allow the cuurent valued upto some extend as per it rating. If current goes beyond that level anywhere in the circuit, wire melts and the connection is broken. Thus, fuse can protect the whole system.

There are two types of fuse basically.

- Replacable (can't be reused again anyhow)

- Rewirable (can be reused again after rewiring of the wire)

Fuse rating can be decided from the total allowable current from the circuit. 

As total load is 10A from the battery, the nearest possible standardized fuse at higher side. So the fuse rating must be of (>10 A), but the nearest valued.

Other aspect need to be considered is the C-rating also. 

Here, we are considering max current drawn from the battery is 10 A irrespective of the battery's C-rating.

The standard for Ampere rating of fuses having std fuses of 15, 20, 25, 30, 35, 40, 45, 50, 60, ........., 6000 Amp as per the circuit requirement. Addition std are of 1, 3, 6, 10 and 601 Amp.

In the given case, total load is 10A, so 10A fuse can't be used and after that 15A fuse comes in std rating. 

So I would suggest the fuse with the 15 Amp current rating for the given case.  

If the total load is of 500 W, many battery can be made to fulfill the energy requiremnt by choosing different combination of Voltage and Current capacity.

In this case, battery with higher valued voltage should be considered to get minimum Copper Loss.

One more consideration can be the time duration of the 500W load. Accordingly, battery voltage and current capacity can be recommandend. Considering the load for an unit hr or one hr.

Let us consider, the Li-ion cell having, 3.7 V and 2.6 Ah capacity, I would like to consider having battiery with the 48 V

              Cells in Series should be 13. As 3.7V*13=48.1 V

                   Now, P=V*I

                           I = 500/48.1

                             = 10.395 Ah

             Cells in Parallel should be 4. As 10.395 Ah/ 2.6 Ah = 3.99

                           I = 4*2.6 = 10.4 Ah

                    and P=V*I=48.1*10.4=500.24 Wh

So, I would recommand the battery with 500.24 Wh (48.1 V and 10.4 Ah). 

And if we goes with the given Voltage of the Battery

Here, using the hint given in the question itself and considering the Battery Voltage = 12 V and considering the load for an unit hr or one hr.

We know, Power (Wh) = Voltage (V) * Current Capacity (Ah)

               500 Wh = 12 V * Current Capacity (Ah)

               Current capacity (Ah) = 500 / 12

               Current Capacity = 41.67 Ah

So, I would recommand the battery with 500 Wh (12 V and 41.67 Ah).

Elements are said to be in parallel, if the path of the current flowing through is more than one. In parallel circuit, both terminals/nodes of both elements are common. Voltage across the elements connected in parallel is same.

Parallel connection are made in cases, where other elements need to be in oprating condition in case of failure of other elements in circuit. So current can pass through the prioritized elements can be operated. 

After observing given Electric Circuit Diagram, such systems are Ignition system, Accessories system and Current & Voltage regulator. They are connected in Parallel after the Ammeter. Many other subsystems are also connected in parallel after the fuse and foot selector switch. 

In any automotive circuit, Ignition System and accessories system are always set to be in Parallel, because to start the vehicle is the first priority of any vehicle, than accessories system, like, tails lights, head lamps. In case of failure of in any accessories, the failure of Ignition system can't be tolarated and thus they are always connected in Parallel.

Elements are said to be series, if there is only one path for the current to pass. In series circuit, only one terminal/node of both elemements is common and that too having opposite polarity. Current across the elements connected in series is same.

Series connection are made in cases, where two elements need to be operated simultaneously and in case of failure in any of the element, other should be disconnected for the safety purpose or functionality purpose. 

After observing given Electric Circuit Diagram, such systems are Fuse and Accessories system. They are connected in series just after the Ammeter. Between Ammeter and Accessories sytem, Fuse connected in series. In case of failure or shorting in any accessory, input from the Ammeter is disconnected and thus safety of that perticular element is ensured. 

In any circuit, Fuse and accessories system are always connected in series, beacause in case of failure of one element, other element is also disconnected automatically. On other side, we can ensure that both elements are getting the same valued current by connecting them in series.