STARTING SYSTEM

STARTER MOTOR BENCH TESTING AND REPAIR


Today in class we learnt about starter motors. We Learnt how a starter motor works and operates and the function of each component in a starter. My understanding of the starter motor is very important in now day cars. As withought a starter your car cant start. Starter motor works through get power from the battery, so it very important to have a battery which is charged. Basically starter motors change electrical energy to mechanical. When we turn the ignition the solenoid recieves current from the battery which makes a magnet pulling the plunger back, this engages the pinion to the fly-wheel. Once plunger gets pulled back it makes a connection so that current can flow from the battery to the starter. Current passes through the brushes to the commutator which spins and transfers current to the windings. The magnetic feild created and the poles repel which turns the armature which the spins flywheel and cranks the engine over.

In practical we went on to  some test's on the starter motor to see if was operating correctly and then we disassembled it and identified the componets and did some tests on them and then reassembled it to see if was working correctly.
The first test we did on the starter was a no load test using the bench tester. The voltage reading we got was 13.37 volts which is well over the specification of 11 volts, and a current reading of a 37.4 using the clamp meter which is between the spec of  30-50 amps. We then started to disassemble the starter and did some test's on the components of it. we also did a visual check to see any signs of over heating,burning or any physical damage. There were no signs of any of this and the starter was in good condition. We first did a ground circuit test between each of the commutator segements and the armuture shaft. We got a reading of infinity which meant it is an open circuit and its not grounding to the shaft which is good. We did a continuty test between each commutator segment. We got a reading of 0.6 ohms, this means there is a circuit with no resistance which meant it passed.
We  checked the length of the brushes to see if was making good contact with the commutator. All of them were well over the spec mark of 5mm meaning that it was making good contact. After the break we got on to testing the solenoid and testing  the pull in windings. We connected the 9 volt power supply to the S and M terminals for no more than five seconds, when we connected it the plunger was getting pulled in and was drawing 10 amps. We then moved on to testing the hold in windings. We connected the 9 volt power supply to the S terminal and the solenoid body, it held the plunger in and drew 7 Amps of current, which is within the spec of 5-8 Amps.

Logic Probe

On friday we were to make a logic probe using the practical book as a guide and help from prem and sefa., Equipment we used was :

• Brass rod
• Red and Green LED
• Black and Red wire 2 meters long
• 2 resistors 1k ohm
• Red and Black aligator clip
• Soldering iron
• 12v power supply
• 100mm plastic tube 7mm ld

We connected te red clip to positive and black to negative.Both red and green LED's lighted up. This shows us that the component is working and there is good connections. When we touched the brass probe end to the positive battery terminal the green LED goes out, this is because when you put positive to positive there is short circuit, so there is no green LED light. When we touched the probe to the earth battery terminal the red LED goes out and the green got brighter, this is because there is a short circuit in the green LED so there is 12v going to red LED so therefore it gets brighter.

Battery

 Testing a automotive car battery off car. The battery's brand made name was LUCAS,The battery number was 128HD, and the cca rating  (cold cranking amps) was  400A, it was not a maintaenece free battery was a conventional type so we could not do a visual check of batterys state of charge but we have to do a hydrometer test .

Before we started the battery test, we had to carry out some visual inspections first of the condition of the battery.We check to see if there was any corrosion on the battery surface and that there is no acid on battrery casing or by terminals.  The terminals were clean and tight, no signs of warpage or expanding of battery case or swelling caused by over charging or cracks in case.The caps were also nice and tight with no showings of possible cracks in them from where the electrolyte can leak from. The battery had passed the visual inspection.

We checked electrolute level by first removing the caps in each cell . All six cells were showing a high level of electrolyte.

We did a (ocv) test and it gave us a reading of 12.6. this meant that the battery was a 100% charged. The specified voltage was 12.4 or above. This meant we could carry on testing the battery.

We performed a specific gravity test on all the cell's. All the cells gave a reading of 13.06 which is the colour green on the hydrometer. The allowable specific gravity variation is 25-50.we got 50. This reading tells us the state of charge of the battery. So we now know that the battery was fully charged.

We continued with batterys and we went on to doing a high discharge test on the battery.To do a high discharge test needs to know the cca rateing before we can put a  load on, the load should only be put on for no more than 15seconds. To do the high discharge test the battery has to be 50% charged (12.4volts). The battery we were going to do the test on was 100% charged. The load we applied to the battery was 155A which is half of the battery cca Rating which was 310. The voltage that was held by the battery while the load was being applied was 9.5volts.

Safety

When we started 4841 Electrical and Electronic course we talked about the importance of safety in a workshop (workplace) and safety when dealing with electricity. We coverd things such as general hazards in the workshop,how to avoid hazards or danger,and what to do minimise or isolate hazards. We also talked about what to do in case of an emergency's, where the evacuation points could be, and where fist aid kit might be located  and where are the emergency exits and where the fire extinguisher are located.

We also talked about how to keep onself protected in the workplace and how to keep your fello co-workers safe.What i learnt during this lesson was that personal protection equipment must be worn whenever working in the workplace,equipment  like steel cap boots and overalls at all times and how they protect you in case of accident. We got told that  if we came with no steel cap boots or overalls to a practical class we will not be allowed in.This is just to protect us from any accidents happening,and to prevent us from getting hurt.

Some of the potential risks and hazards that we need to know when we are working in the place are do not remove  cap's such as radiator caps that contanis hot or high pressure fluid. Wait untill engine cools down. Always use axle stands when jacking car up,never rely on hydraluic jack alone. Never smoke in the workshop,if u need to smoke go out side and smoke away from the building. We also  need to take care of short-circuit's or electric shocks when working where there is electricity.

CHARGING SYSTEM

ALTERNATOR ON CAR TESTING




Today  in practical we did alternator on car testing. WE started by carrying out some visual checks first be we started any testing as this is safe and will give a good and accurate reading. We checked that there were proper connections and that nothing was loose.  After this we carried out a no load test with none of the accessories on  and engine running at about 1500 rpm. We recorded the battery's ocv which was 12.3, after that we checked the regulator voltage reading which gave us a reading of 12.3 which is below the spec range of 14.5 and 14.6. The last test on no load was the output amps test. We did this by putting a clamp meter through battery wire which goes to the alternator, we got a reading of 0.2 which well below the spec of 5 and 12. This reading can vary due to the state of charge of the battery and the current needed to run the engine. After break we came back and prem had bring the carbon pile so that we can use it to put a load on the alternator. we did the output amps check again but when it was under load we got a reading of 29.1 Amps And the charging voltage under load to be 12 Volts. These test's show us that the alternator is correctly charging the battery when there is a load put on, it is out putting the right amount of current and that the alternator is able to hold the load. If for example the alternator was out putting less amps it would mean the the battery would be getting drained and that the alternator is at fault and not working properly. The last test we did was a voltage drop test, first was from the battery to the alternator we got 0.17 which is a pass and it needed to be under .2 volts. This just tell's us that there is no extra voltage being used up some where. We also did a voltage drop test between battery negative and alternator body to check if there was any loss of volts in the grounding of circuit.






















ALTERNATOR OFF CAR TESTING




Today in practical we got to dismantle an alternator and check the different components of it. First we took the rear cover off  and the regulator and the brush holder on the alternator. The first test we diid was the rotor winding to ground test i place the black lead of the meter to the rotor shaft and the red lead on the slip rings. I got a reading of infinity this is because there is no circuit between the shaft and slip ring. If i did get a reading it would have meant that the rotor winding has been shortened to ground and should be replaced. After that we did the rotor winding internal resistance test and we got a reading of 3.1 ohms. This meant that there is a circuit between the slip rings. After that i removed the rectifier and the housing. Then we tested the stator winding to ground test and we got a reading of infinity this is because there should be no circuit between the circuit and ground. We then tested the voltage regulator, the short circuit light was off signaling no short circuit. The warning light came on and stayed on as well as the field light continuously flashing meaning we had wired it up properly. We got a set point voltage spec of 14.5 meaning the output voltage will not exceed this in controlling the strength of the magnetic field. The last check we did was checking the length of the brushes. The minimum requirement of the length of brushes was 4.0mm, we got 8mm which meant the brushes had constant contact with the slip rings so that it can supply electricity efficiently.

Circuits

Today we did Electricity Circuits individual,Series,And parallel Circuits in practical class. I created a Series circuit on the boards using a battery source,a light bulb switch and wires. I measured the available voltage using a voltmeter..What i found was that as the voltage passes through the different components the voltage starts to drop slightly..the most voltage drop occured at the terminal after the light bulb and at the negative of 12v supply.this is because the bulb is the consumer it uses the most volts..



Terms I Learnt:


Available Voltage:
Is voltage that is available for a consumer to use...We can use a multi meter to do this, by putting black lead from multi meter to ground and red lead to point where we want to measure.

Voltage Drop:
Is how much voltage has been taken by each components (consumers) in a circuit. We use a multi meter and by placing both leads on either side of component.

Series Circuit: Is a circuit with 1 conducting pathway

Parallel Circuit: Is a circuit with 2 or more conducting pathways

Compound Circuit: Circuit which within is a combination of both series and parallel circuits. 

In a series circuit, the voltage is shared between all components, the amps remain the same throughout the circuit. The total voltage is the sum of the voltage through each component.

In a parallel circuit voltage remains the same at each component.but amps are shared through each component. Thus the total current is the sum of the currents through each component.

I learnt how to calculate resistance of light bulb using ohms law by using volts,amps,and resistance...we need to of these to calculate the third part of equation..i also learnt the power law for calculating watts used at light bulbs..we went on carrying out the practical on differen sizes of light bulbs and connecting them in parallel and series which gave us different readings...Experimenting with series and parallel circuits and interpreting the readings we got gave me a clear understanding on voltage drops and current flow in different circuits..