Headlight circuit 01/03/2012

Headlight diagram

Components

• battery
• wire
• fuse
• relays x2
• headlight bulbs x2
• switch

Function

The battery supplies the power

Wires carry it through the fuse the relays to terminal 30

The relays function as a remote switch, the main current flows from the battery to the user or headlight bulb. The terminal number is generally 87 or 87a.

It is activated by low current coil that acts as a magnet  to close the switch. Terminal numbers are 85 + 86 terminal 85 goes to a earth or ground source. Terminal 86 supplies power through a switch to complete the circuit

Measuring the volts, amps and ohms in a car 29/02/20012

checking Amps (current draw)

1. disconnect the negative battery terminal
2. change the setting on the multimeter to amps
3. plug the wires in to the right ports on  the multimeter (images/labels indicate which port to use)
4. connect the the multimeter in series from the battery to the terminal cable
5. the reading will be displayed on the screen (Make sure that all the appliances are switched off)
6. disconnect the multimeter and replace the terminal cable

checking Volts (charging rate)

1. make sure the wires are in the right ports on the multimeter and that it is on the right setting
2. connect the multimeter to the battery in parallel
3. the reading will be shown on the screen
4. start the car and check the reading again, it should be more than the original voltage if not then the alternator is not charging
5. remove the multimeter

Checking ohms (checking to see if components work)

1. make sure there is no power on the component 
2. set the multimeter to the ohm setting 
3. connect the wires to the components terminals 
4. the ohms should appear on the screen

check that the multimeter is set to the right range when using all of the settings

Electrical systems 28/02/2012

Electrical Systems

·         Ohms law: ohms law states that the potential difference (volts) is equal to the resistance (ohm) multiplied by the current (amps).

·         Therefore :

            V = I x R

            
                R = V / I

            
                I = V / R

Series and parallel

If batteries are connected in series the volts add up but the amps stay the same

If batteries are connected in parallel the volts stay the same but the amps add up

When resisters are connected in series the ohms add up and in parallel the ohms are worked out using the formula  Rt = (R1 x R2) / (R1 + R2) 

If components are connected in series the volts is the sum of the drop over the resistance the current stays the same throughout the circuit. If the components are connected in parallel the voltage is the same for all the components but the current drops.

Measuring ohms, amps and volts using a multimeter

1.      Check that the cables are in the right ports (indicated by labels)

2.      Set the multimeter to the right setting

3.      For the potential difference (volts) connect the cables in parallel to the component that needs to measured

4.      For the current (amps) connect the cables in series  to the circuit

5.      When using the ohm setting to measure the resistance make sure that all the power is disconnected from the component to be measured, if not the multimeter may get damaged.

Health and safety

·         Always follow the warning signs and wear the right protective equipment

·         Look out for hazards while working and either solve the problem or tell someone who can

·         Beware of poisonous fumes that are given off while working on a car

·         Do not expose your skin to car oil for long periods of time, wear gloves or a barrier cream

·         Beware of hot engine/car parts

·         Do not work under car that is only jacked up, use axel stands

·         Be careful when working with fuel lines that are under pressure

·         Wear safety glasses  when working under cars