The first week of the course was made up of safety and electrical circuits.
Safety outlined all the hazards that are associated when working on cars. for example never rely on a hydraulic jack always place axle stands under the car.it taught us to be carefull and safety alert when doing anything on ar around the vehicle.
There are 4 types of circuits, individual, series, parallel and compound. all these circuits have laws that go with them.
In a series circuit the current will be the same anywhere in the circuit. The total resistance in the circuit is the sum of each resistive unit. The voltage drop across each resistive unit when added up will equal the total available voltage to the circuit. The part that has the highest resistance will use most of the voltage no matter where it is in the circuit.
In a parallel circuit the total amperage equals the sum of all the current branches, the total resistance of the circuit will be less than the lowest resistor. The available voltage will be the same at every branch.
There are laws that are used to work out amperage, volts, and resistance. The law is called Ohms law. You can work out power using the power law as long as you have the voltage and amp readings. To measure total resistance in a parallel circuit is different, there is a special formula to use: 1/rt=1/r1+1/r2. If you have more than two branches you just keep on going with the formula. e.g 1/rt=1/r1+1/r2+1/r3 etc.
Week 2
In week two we covered batteries and starter motors.
We learnt how to properly test a battery to make sure it will give enough amperage and voltage when starting. As most starting problems are caused by the battery it is very important to have a good battery in the vehicle. The first thing we do on a battery is carry out a visual check, check for signs of damage, swelling and condition of terminals and wires. Next thing you do is check the electrolyte levels in each cell. if there is no evidence of the battery leaking and electrolyte levels are low, it can indicate a high charging rate or faulty cells. After that we carry out an OCV test, but we first needed to get rid of the surface charge on the battery so the engine was disabled and cranked over a few times. you could get rid of the surface charge another way by turning the headlights on for one minute. to do any further tests the battery must be at least 50% charged which is 12.4v. If the battery is not 50% charged it will need to be charged. The next test is to use a hydrometer in each cell and take a reading. A fully charged battery should have a reading of 1.265 to 1.235, if the battery is below spec. it will need recharging or could even be defective. the allowable specific gravity variation of a battery is 50 points. Next a load test is carried out on the battery. To work out the load to apply you need to know the cold cranking amps and divide it by 2. The voltage must hold above 9.5v when the load is applied. The last test to be done was a parasitic draw. The amperage draw should not be more than 1 amp.Before removing a battery it is important to check if the vehicle requires a booster pack. The booster pack will keep all the memory stored on the computer, this is more important on cars with automatic transmissions as shift patterns could be lost. When removing a battery all ways disconnect the negative lead first and when fitting the battery connect the negative lead last.
Starter motor. We stripped down the starter motor and tested the individual components of it. The first test done was on the armature. We tested for shorts to ground, if it was shorting to ground it would not produce a strong enough magnetic field to turn. Commutator continuity was tested. We done a visual check first of all on the armature, we were looking for signs of damage or wear. a overheated armature usually throws solder from the commutator area. The easiest way to check the armature and commutator would be by using a growler. A growler effectively does the same job as a multimeter but it is quicker to use. next we tested the field coil windings.We checked continuity and resistance in them. Field windings should not be grounded to the starter body so you should get an infinity reading. The brushes where tested to see if they are in specification. we measured the length of them. If they where to short they might not make good contact between the commutator. Then we tested brush holder assembly to see whether the insulated brushes were shorting to ground, the reading on the ohms meter should be infinity. Last component to be tested was the solenoid. in the solenoid there are two windings, the pull in winding and the hold in winding. We used a power supply dialed up to 9v maximum. The leads where connected to the S and M terminals and a specification for the current draw was given. This was not done for more than 5 seconds to prevent heat damage. Then we tested the hold in winding. We pushed down the plunger and connected the leads to the S terminal and the body of the solenoid and then released the plunger to see if the winding was working.
Week 3
In week three we started on charging systems. The first thing we did was strip down an alternator but we were careful to follow the instructions in the book. The first tests done where on the rotor. We tested the rotor if it was shorting to ground then the resistance of the slip rings on the rotor. Each end of the rotor windings are connected to one of the slip rings. Next thing to be tested was the stator windings. there are two types of stator windings, Delta and Star wound. delta wound alternators have the ends of the wires connected end to end with no neutral junction. In this type of alternator two circuit paths are formed between the diodes during each phase. They are usually used in high output alternators. Star wound stators have wires of the stator connected to a neutral junction. Star wound alternators provide good current output at low rpm. Then we tested the rectifier diodes. Diodes are used in the alternator to convert a.c into d.c. If a diode was broken you would be able to see that with out dismantling the alternator by using a voltmeter connected to the battery. The voltmeter would not stay constant and would go up and down because some of the current is a.c. Last thing to be tested on the alternator was the transpo regulator tester. We were given a wiring diagram to show us how to hook it up. There are light to look at when using the tester. Short circuit light, this should be off. Warning light, should come on and stay on. Field light, should flash continuously.
Resistors.We were taught how to identify resistors by the colours on them. There are two resistors, 4 band and 5 band. the way to work out the resistance of the resistor is: the first two or three bands may be the numbers to write down, the next band is the multiplier, the last band to the right is the tolerance value. We did tests to see the different laws of electricity at work. When the two resistors where connected in series the resistance total equaled the sum of both resistors, and when we connected them in parallel the total resistance was less then the lowest resistor.
Week 4
Capacitors. A capacitors stores an electric charge. We did a test on capacitor to see the charge rate of them. we calculated how long it would take to charge with a certain resistor in series with it. What we found was that in the first 10 seconds it draws nearly all of its capacity, but it has not reached the maximum voltage. After it has drawn in nearly all the voltage it then tries to squeeze in every last bit of voltage thats why it takes a while for it to get to its maximum voltage. The capacitor discharges its load instantaneously. Capacitors can also be used to dampen voltage spikes, like in the ignition circuit capacitors would be used.
We had practice at alignment of headlights using the V.I.R.M to get specifications. We used a headlight alignment tool which gave us the Lux reading. Using the Lux reading we can see if the headlights are the similar to one another and the alignment markings on the tool to see if the lights were aiming in the right place. The tool must be between 30 cm and 70 cm away from the front of the car.
We had to find faults in a vehicle lighting system. We were given wiring diagrams and the lecturer set faults in the system. We used a multimeter and went through each step to eliminate where a possible fault might have been.
Week 3
In week three we started on charging systems. The first thing we did was strip down an alternator but we were careful to follow the instructions in the book. The first tests done where on the rotor. We tested the rotor if it was shorting to ground then the resistance of the slip rings on the rotor. Each end of the rotor windings are connected to one of the slip rings. Next thing to be tested was the stator windings. there are two types of stator windings, Delta and Star wound. delta wound alternators have the ends of the wires connected end to end with no neutral junction. In this type of alternator two circuit paths are formed between the diodes during each phase. They are usually used in high output alternators. Star wound stators have wires of the stator connected to a neutral junction. Star wound alternators provide good current output at low rpm. Then we tested the rectifier diodes. Diodes are used in the alternator to convert a.c into d.c. If a diode was broken you would be able to see that with out dismantling the alternator by using a voltmeter connected to the battery. The voltmeter would not stay constant and would go up and down because some of the current is a.c. Last thing to be tested on the alternator was the transpo regulator tester. We were given a wiring diagram to show us how to hook it up. There are light to look at when using the tester. Short circuit light, this should be off. Warning light, should come on and stay on. Field light, should flash continuously.
Resistors.We were taught how to identify resistors by the colours on them. There are two resistors, 4 band and 5 band. the way to work out the resistance of the resistor is: the first two or three bands may be the numbers to write down, the next band is the multiplier, the last band to the right is the tolerance value. We did tests to see the different laws of electricity at work. When the two resistors where connected in series the resistance total equaled the sum of both resistors, and when we connected them in parallel the total resistance was less then the lowest resistor.
Week 4
Capacitors. A capacitors stores an electric charge. We did a test on capacitor to see the charge rate of them. we calculated how long it would take to charge with a certain resistor in series with it. What we found was that in the first 10 seconds it draws nearly all of its capacity, but it has not reached the maximum voltage. After it has drawn in nearly all the voltage it then tries to squeeze in every last bit of voltage thats why it takes a while for it to get to its maximum voltage. The capacitor discharges its load instantaneously. Capacitors can also be used to dampen voltage spikes, like in the ignition circuit capacitors would be used.
We had practice at alignment of headlights using the V.I.R.M to get specifications. We used a headlight alignment tool which gave us the Lux reading. Using the Lux reading we can see if the headlights are the similar to one another and the alignment markings on the tool to see if the lights were aiming in the right place. The tool must be between 30 cm and 70 cm away from the front of the car.
We had to find faults in a vehicle lighting system. We were given wiring diagrams and the lecturer set faults in the system. We used a multimeter and went through each step to eliminate where a possible fault might have been.
