Describe the terms Conduction, convection, and radiation, and where would you find them on an car engine?
Conduction: Heat transfered to a solid. Transfered from the piston to the cylinder bore.
Convection: Heat transfered through a liquid medium. From the cylinder block to the coolant and into the radiator.
Radiation: Heat trasnfered from a liquid or solid to a gas. Heat that is taken away from the radiator by air going passed it.
What is the purpose of a thermostat?
It restricts the amount of coolant that flows into the engine until it is up to operating temperature.
Why do engines have coolant in them?
It prevents bubbles from forming in the water. If bubbles form they can act as an abraisive to the water jackets. It also prevents the water from boiling and creating high pressure due to the steam build up. It also prevents the coolant from freezing in sub zero conditions.
When should an oil filter be replaced (miles)?
Every year or around 6,000 - 10,000 Km
What projects the oil pressure and where is it situated?
The oil pump which is located on the cylinder block next to or on, and is run by, the crankshaft.
Thursday, 26 May 2011
Tuesday, 19 April 2011
Relays
A relay is a component that uses a electromagnetic switch to create contact between wires. There are 2 relays we used. A two switching circuit and a one switching circuit.
These are the terminals and what they do.
86 - positive side of control circuit
85 - negative side of control circuit
30 - battery supply for switched circuit
87 - open circuit when relay is off
87a - Closed when circuit is off
A low amp current goes through 86, through windings around an iron core creating an electro magnet and out terminal 85 to ground.
This electro magnet pulls a pin/switch down onto the contacts 30 and 87 completing the circuit and turning on any components wired to the 87 side side of the relay.
In the off position the relay recieves voltage but doesnt consume any between 86-85 there is no resistance because the relay is not on. there is no voltage in terminal 87 because the contacts are open and cannot recieve any voltage.
When the switch is on the relay is consuming voltage and none is left when it gets to terminal 85. There is now full available voltage at 87 because the switch is closed.
These are the terminals and what they do.
86 - positive side of control circuit
85 - negative side of control circuit
30 - battery supply for switched circuit
87 - open circuit when relay is off
87a - Closed when circuit is off
A low amp current goes through 86, through windings around an iron core creating an electro magnet and out terminal 85 to ground.
This electro magnet pulls a pin/switch down onto the contacts 30 and 87 completing the circuit and turning on any components wired to the 87 side side of the relay.
In the off position the relay recieves voltage but doesnt consume any between 86-85 there is no resistance because the relay is not on. there is no voltage in terminal 87 because the contacts are open and cannot recieve any voltage.
When the switch is on the relay is consuming voltage and none is left when it gets to terminal 85. There is now full available voltage at 87 because the switch is closed.
Logic probe/diodes
We made a logic probe which uses Light emiting diodes to indicate whether it is the positive side or negative side.
Diodes work only by letting electricity flow one way through the circuit. This is what makes the logic probe work.
When the positive and negative leads are hooked up to the power supply, I touched the probe to the positive side and the green LED went out. This indicates to me that this is the positive side. The opposite happened when I touched it to the negative side, the red LED went out, indcating to me this is the negative side.
The reason Why this happens is because electricity can only flow one way through a diode. When the positive terminal is touched this creates a short circuit and only allows the current to flow through the red LED and not the green one. When the negative side is touched there is another short circuit and this time it goes straight to ground before it can go through the red LED.
Also when each LED goes out the other one gets brighter. This is because they are wired in series and are sharing the voltage. When one isn't being supplied voltage the total available voltage is supplied to the one that is lit and it glows brighter.
Diodes work only by letting electricity flow one way through the circuit. This is what makes the logic probe work.
When the positive and negative leads are hooked up to the power supply, I touched the probe to the positive side and the green LED went out. This indicates to me that this is the positive side. The opposite happened when I touched it to the negative side, the red LED went out, indcating to me this is the negative side.
The reason Why this happens is because electricity can only flow one way through a diode. When the positive terminal is touched this creates a short circuit and only allows the current to flow through the red LED and not the green one. When the negative side is touched there is another short circuit and this time it goes straight to ground before it can go through the red LED.
Also when each LED goes out the other one gets brighter. This is because they are wired in series and are sharing the voltage. When one isn't being supplied voltage the total available voltage is supplied to the one that is lit and it glows brighter.
Starter motor
The first test we carried out on the starter motor was a visual test to check for any burning, overheating, poling and physical damage. There was none of this except for very minor scratching.
Testing if there is a short circuit between the commutator segments and the armature core. I placed the multimeter set to Ohms on the two. The reading was infinite telling me there is no short circuit and that is what it was supposed to be.
Checking continuity between the comutator segments. Place one probe one of the segments and with the other move it around the others checking if there is a break on any of them. There was continuity in all of the segments.
Measuring the commutator I should have gotten in the range of 26.8 and 31mm. I got 31mm. The mica undercut should have been between 0.7 and 1mm. I got a measurement of 1mm.
Testing for runout on the armature shaft I placed the armature between two 'V' blocks. I rotated the armature 360 degrees while reading the dial test indicator (it is set up on the armature core). The runout should be no more than 0.2mm. I got a maximum reading of 0.1mm.
We also tested continuity and grounding in the field coils.
The brushes should be no less than 5mm. All of the brushes were greater than the specified length.
Testing if there is a short circuit between the commutator segments and the armature core. I placed the multimeter set to Ohms on the two. The reading was infinite telling me there is no short circuit and that is what it was supposed to be.
Checking continuity between the comutator segments. Place one probe one of the segments and with the other move it around the others checking if there is a break on any of them. There was continuity in all of the segments.
Measuring the commutator I should have gotten in the range of 26.8 and 31mm. I got 31mm. The mica undercut should have been between 0.7 and 1mm. I got a measurement of 1mm.
Testing for runout on the armature shaft I placed the armature between two 'V' blocks. I rotated the armature 360 degrees while reading the dial test indicator (it is set up on the armature core). The runout should be no more than 0.2mm. I got a maximum reading of 0.1mm.
We also tested continuity and grounding in the field coils.
The brushes should be no less than 5mm. All of the brushes were greater than the specified length.
Alternators
Alternators are what powers the cars eletronics and charges the battery when the car is running. It is run straight from the crankshaft by a belt.
The first test we did was a visual check for any damage on the outer case. Then we removed the rear cover to expose the components. we then removed the brushes, the regulator and the rectifier.
I carried out a test to make sure the rotor shaft and the slip rings have no circuit between them. I placed the multimeter set to Ohms, one lead on the rotor shaft and one lead on the slip rings. The meter should read infinity meaning that there is no circuit between the two. There was no circuit.
Testing the rotor winding internal resistance I touched one lead to one slip ring and the other lead to the other slip ring. The reading should be within 2 and 6 Ohms. I got a reading of 2.8. This was a suitable reading which means it has passed.
Testing the stator winding resistance I connected the black lead to the common point and then touched each of the other terminals one after the other. the readings should be within 0.0 and 0.2 ohms. I got a reading of 0.0 Ohms. Then to test the stator winding to ground I attached the red lead to the common terminal and the black to the body of the altinator. There should be no connection so the reading should be infinite. This is what I got so there is no connection between the stator windings and the altinator body (ground).
Testing the rectifier diodes. Setting the multimeter on diode test mode I placed the common lead on the B terminal and touched the positive lead to each of the P terminals (where the diodes conect to the stator windings). I recorded my readings. The readings were all within the specs of 0.5-0.7 except one. The one that failed I got a reading of infinity, this was because it was the common point and has no connection to the B terminal.
If I put the cables on the opposite terminals I got an infinite reading for all of the diodes. This is beacause diodes only let electricity flow one way in a circuit.
Testing the Negative diodes is almost the same only touching the negative lead to the E terminal (body of the rectifier) and the postive to each of the P terminals. I should have got an infinite reading for each of the diodes which I did. Testing with the leads swapped over, I got readings which were in the specs of 0.5-0.6.
Measuring the brushes they should all be above the minimum length of 4.0mm. My brushes were both at 6.0mm.
The first test we did was a visual check for any damage on the outer case. Then we removed the rear cover to expose the components. we then removed the brushes, the regulator and the rectifier.
I carried out a test to make sure the rotor shaft and the slip rings have no circuit between them. I placed the multimeter set to Ohms, one lead on the rotor shaft and one lead on the slip rings. The meter should read infinity meaning that there is no circuit between the two. There was no circuit.
Testing the rotor winding internal resistance I touched one lead to one slip ring and the other lead to the other slip ring. The reading should be within 2 and 6 Ohms. I got a reading of 2.8. This was a suitable reading which means it has passed.
Testing the stator winding resistance I connected the black lead to the common point and then touched each of the other terminals one after the other. the readings should be within 0.0 and 0.2 ohms. I got a reading of 0.0 Ohms. Then to test the stator winding to ground I attached the red lead to the common terminal and the black to the body of the altinator. There should be no connection so the reading should be infinite. This is what I got so there is no connection between the stator windings and the altinator body (ground).
Testing the rectifier diodes. Setting the multimeter on diode test mode I placed the common lead on the B terminal and touched the positive lead to each of the P terminals (where the diodes conect to the stator windings). I recorded my readings. The readings were all within the specs of 0.5-0.7 except one. The one that failed I got a reading of infinity, this was because it was the common point and has no connection to the B terminal.
If I put the cables on the opposite terminals I got an infinite reading for all of the diodes. This is beacause diodes only let electricity flow one way in a circuit.
Testing the Negative diodes is almost the same only touching the negative lead to the E terminal (body of the rectifier) and the postive to each of the P terminals. I should have got an infinite reading for each of the diodes which I did. Testing with the leads swapped over, I got readings which were in the specs of 0.5-0.6.
Measuring the brushes they should all be above the minimum length of 4.0mm. My brushes were both at 6.0mm.
Batteries
When we first got the batteries there were 2 terminals (one positive and one negative) and several screw caps. These screw caps let you get to the electrolite inside.
The first test we did was a visual inspection of the battery for corrosion and deformation/warping of the battery. We also should make sure there is no leakage of electrolite and the battery clamp bolts are tight. If there was some corrosion on the terminals we would need to clean it with some water and baking soda.
Another visual check was of the electolite levels. If they were just covering the plates inside then they were at a satisfactory level.
Checking the OCV (open circuiut voltage) we put the voltmeter accross the terminals on the battery.
Anything under 12.4V you would have to charge the battery before continuing with testing. My battery was 12.8V so I could continue with testing.
Next test is the specific gravity test. This is the difference between the highest hydrometer reading and the lowest. My specific gravity variatin was 0.1 which is in the good range (0-0.5)
Next was the high rate discharge test. The CCA (Cold Cranking Amps) of my battery was 410A. This means I have to apply a load of 205A (half the CCA). The voltage of the battery must hold above 9.5V while the load is applied for 15 sec.
The voltage held while the load was applied was 10V which is a pass.
The parasitic draw test is when you attach a multimeter set to amps in series with the battery circuit. The ammount allowed is 0.3mA. My result was 0.25mA which is ok.
Sadly we did not get to do any work with a digital battery tester.
The first test we did was a visual inspection of the battery for corrosion and deformation/warping of the battery. We also should make sure there is no leakage of electrolite and the battery clamp bolts are tight. If there was some corrosion on the terminals we would need to clean it with some water and baking soda.
Another visual check was of the electolite levels. If they were just covering the plates inside then they were at a satisfactory level.
Checking the OCV (open circuiut voltage) we put the voltmeter accross the terminals on the battery.
Anything under 12.4V you would have to charge the battery before continuing with testing. My battery was 12.8V so I could continue with testing.
Next test is the specific gravity test. This is the difference between the highest hydrometer reading and the lowest. My specific gravity variatin was 0.1 which is in the good range (0-0.5)
Next was the high rate discharge test. The CCA (Cold Cranking Amps) of my battery was 410A. This means I have to apply a load of 205A (half the CCA). The voltage of the battery must hold above 9.5V while the load is applied for 15 sec.
The voltage held while the load was applied was 10V which is a pass.
The parasitic draw test is when you attach a multimeter set to amps in series with the battery circuit. The ammount allowed is 0.3mA. My result was 0.25mA which is ok.
Sadly we did not get to do any work with a digital battery tester.
Compound circuits
I didnt quite understand the workings of the compound circuit but here is what I found out.
There is two bulbs wired up in parallel and 1 in series.
When I wired it up at first the bulbs in the parallel circuit were hardly lit and the series bulb glowed bright.
I think this was because the series bulb was wired after the parallel circuit and because the resistance of the parallel was less than that of the series it used all of the voltage to power it leaving very little for the parallel bulbs resulting in them not lighting up.
There is two bulbs wired up in parallel and 1 in series.
When I wired it up at first the bulbs in the parallel circuit were hardly lit and the series bulb glowed bright.
I think this was because the series bulb was wired after the parallel circuit and because the resistance of the parallel was less than that of the series it used all of the voltage to power it leaving very little for the parallel bulbs resulting in them not lighting up.
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