First of all, we had to identify the direction of flow through the diode. This is done by 1: Visual inspection of the diode itself shows that one end is painted which shows that it is the cathode end and 2: By measuring the resistance on each side it shows that when it is one way round it will read infinity as there is no flow through, and the other will have a high reading which means it is the anode end.
We had to then measure the resistance of the diode in both directions using the 2K ohms position on the meter:
Anode to Cathode: Infinity
Cathode to Anode: Infinity
It was said that both of these readings were going to read infinity as there should be no resistance within the diode. The voltage supplied was 0.05v which means theoretically there is not enough voltage to push through the bindery layer of the diode and get an accurate reading.
We then had to measure the diode in both directions:
Anode to Cathode: 0.683v
Cathode to Anode: Infinity
Explain what the Diode Test Position readings means when you test the diode in both directions and describe whether the diode was good or bad:
The diode is in good condition as it shows the amount of voltage allowed through in one direction. The other however has no reading, which is as it should be.
After building a circuit with a 1K ohm diode and a resistor, using a 12 volt supply.
Voltage drop across resistor: 13.22v
Voltage drop across the diode: 0.57v
Measure amp flow through the diode: 0.01A
Avaliable voltage at voltage supply: 13.8v
Voltage drop (sum) across the resistor and diode: 13.79v
Apply the rules of Electricity to these readings above and describe how these readings demonstrate the rules of electricity in action:
As voltage is quite high and so is the resistance, there appears to be verylow to minimal amps in the circuit. The resistor, being large allows very little voltage through, so the remainder of voltage in the circuit is below 1v. The diode had a voltage drop of 0.57v which is the remainder of voltage in the circuit. No voltage left as it grounds.
After changing the resistor in the circuit to a 4000 ohm resistor:
Voltage drop across resistor: 13.28v
Voltage drop across diode: 0.5v
Amp flow through D: 0.01A
Describe how this change of resistance lead to changes in your volt and amp readings. Discuss how this demonstrates how the rules of electricity work.
The readings did not change much, if at all,
After testing an LED (Light Emitting Diode):
Anode to Cathode: 1.834v
Cathode to Anode: Infinity
Compare the voltage drop of a normal diode and an LED. What does this tell you?
1.88v of LED, 0.5v for normal resistor. LED needs more voltage to energise it.
We then had to build a circuit with an LED in the diode position with a 1K ohm resistor and a 12v power supply.
Voltage drop across the resistor: 11.77v
Voltage drop across the diode: 1.88v
Amp flow through LED: 0.01A
Avaliable voltage at voltage supply: 13.5v
Voltage drop (sum) of resistor + diode: 13.65v
Apply the rules of electricity to these readings and compare how these readings are different than the readings for the diode above. In other words, how does the difference between a diode and an LED result in different readings for each part? Explain:
The voltage drop of the resistor decreases as more voltage is needed for the LED. The amp reading is still very low though.
Sunday, 15 May 2011
Tuesday, 10 May 2011
Identifying, Testing and Combining Resistors
10th May 2011
We were given 6 resistors and a colour code identification sheet to allow calculation of each specific resistor. The basic principle of the coloured bands is that the last band is the tolerance percentage of the resistor, the 2nd to last the multiplier and the other bands will be the numbers taken down to represent the value of the resistor.
There are 4-Band resistors and 5-Band resistors. This does not necessarily mean that the 5-Band resistor has a greater resistance than that of a 4-Band however. The intensity of the resistor is entirely dependent on the multiplier.
The activity that we were given meant we had to write down each colour in the order it was on each of the resistors and give the value of each based on the identification chart. We then had to figure out the low tolerance value and the high tolerance level of each. From there we were to measure the value with the multi-meter to see if the value was correct and the resistor passed. 4/6 passed and the other 2/6 were unreadable on the multi-meter as they were too high a value.
From that chart we were to choose two resistors from the list we had just made and write the values of these down. From there we had to put the resistors in a series circuit (end to end, one right after the other) and measure the combined value, the result of which was 2,070 ohms. Following that, the resistors then needed to be put in a parallel circuit (both sets of ends connected, almost a circle), the result of which was 78.3 ohms.
REPORT:
What principles of electricity have you demonstrated with this? Explain:
Showed the difference between resistors in series circuit and in parallel circuit. The total resistance in the series circuit is the sum of both the resistors added, however the total resistance in a parallel circuit is divided amongst the different pathways. The total resistance will always be lower than the lowest resistor.
Sunday, 8 May 2011
Relays
6th May 2011
Before we started to do any practical exercises on relays, we were told to read through the notes provided at the beginning of our practical workbooks and show on the 'Sample Wiring Diagram' how each relay is turned on to turn on the fuel pump in the circuit. I found this very effective as it showed the different paths of current and simultaneous switching to eventually lead to the same path.
We then did a few exercises to understand the basic principles of a relay, followed by an exercise involving wiring up a relay in a circuit with 3 bulbs in a parallel circuit (control circuit of the relay being negatively switched) and drawing a diagram of this. It took a while to figure out how this set up worked because in past circuits, we have had to wire the switch directly after the power supply, whereas in this case the switch had to be wired after the bulbs from the relay. From this circuit, we measured the avaliable voltage from the circuit when it was off and when it was on, and compare the difference.
REPORT:
When the circuit is off, each components avaliable voltage is approx. the same as no component is using any voltage from the power supply. However, when the circuit is on, some voltage is being used by the relay to energise the internal magnet, therefore they drop slightly. Terminal 85 however, has 0.14v avaliable. This is because terminal 85 is connected after the bulbs/consumers which are connected in parallel consuming the same amount of energy each. Therfore there is none to minimal voltage left.
We then had to draw a diagram showing how to wire up a relay to switch between two lights, as if switching from high beam to low beam. This was achieved by physically wiring up the board to show a better understanding of the diagram.
Before we started to do any practical exercises on relays, we were told to read through the notes provided at the beginning of our practical workbooks and show on the 'Sample Wiring Diagram' how each relay is turned on to turn on the fuel pump in the circuit. I found this very effective as it showed the different paths of current and simultaneous switching to eventually lead to the same path.
We then did a few exercises to understand the basic principles of a relay, followed by an exercise involving wiring up a relay in a circuit with 3 bulbs in a parallel circuit (control circuit of the relay being negatively switched) and drawing a diagram of this. It took a while to figure out how this set up worked because in past circuits, we have had to wire the switch directly after the power supply, whereas in this case the switch had to be wired after the bulbs from the relay. From this circuit, we measured the avaliable voltage from the circuit when it was off and when it was on, and compare the difference.
REPORT:
When the circuit is off, each components avaliable voltage is approx. the same as no component is using any voltage from the power supply. However, when the circuit is on, some voltage is being used by the relay to energise the internal magnet, therefore they drop slightly. Terminal 85 however, has 0.14v avaliable. This is because terminal 85 is connected after the bulbs/consumers which are connected in parallel consuming the same amount of energy each. Therfore there is none to minimal voltage left.
We then had to draw a diagram showing how to wire up a relay to switch between two lights, as if switching from high beam to low beam. This was achieved by physically wiring up the board to show a better understanding of the diagram.
Wednesday, 4 May 2011
Starter Motor On Car Testing
4 May 2011
These tests were completed on a starter motor on an engine set up outside of a vehicle.
Before carrying out any tests however, the ignition or fuel injection system must be deactivated (which we did by removing the fuse), the battery to be checked for serviceability (after removing surface charge, checking voltage - result 100% - 12.7v), the right range has been selected on the digital meter (20DC volts) and that the vehicle is in neutral, which in this case does not apply.
The avaliable voltage across the battery while cranking needed to be checked, which is specified 9.5v minimum. The result was 11v which is plenty.
We then had to perform a voltage drop test (while cranking) between battery positive and solenoid starter input, across solenod main input and output, and between battery negative and starter motor body. The specifications of these were all very low. The first was specified less than 0.2v, however the result was 0.4v (well over and therefore failed). The second was specified less than 0.1v, and the result was 0.17 which is not too much over but still a fail. The third was specified less than 0.2v and the result was 0.91v which again is too high and failed. The maximum allowable voltage drop across the component is 0.5v and the total turned out to be 1.48v, almost 3 times that value.
The starter motor current draw to be tested using a clamp meter. The specified current draw is 125-150 amps. The test result was 133A which is a pass.
REPORT:
The voltage drop showed increased figures than specified which means there is resistance within the circuitfrom the battery to the starter motor and within the solenoid. Amps however were within specified range. The resistance source needs to be minimised for starter motor efficiency.
Starter circuit test failed.
These tests were completed on a starter motor on an engine set up outside of a vehicle.
Before carrying out any tests however, the ignition or fuel injection system must be deactivated (which we did by removing the fuse), the battery to be checked for serviceability (after removing surface charge, checking voltage - result 100% - 12.7v), the right range has been selected on the digital meter (20DC volts) and that the vehicle is in neutral, which in this case does not apply.
The avaliable voltage across the battery while cranking needed to be checked, which is specified 9.5v minimum. The result was 11v which is plenty.
We then had to perform a voltage drop test (while cranking) between battery positive and solenoid starter input, across solenod main input and output, and between battery negative and starter motor body. The specifications of these were all very low. The first was specified less than 0.2v, however the result was 0.4v (well over and therefore failed). The second was specified less than 0.1v, and the result was 0.17 which is not too much over but still a fail. The third was specified less than 0.2v and the result was 0.91v which again is too high and failed. The maximum allowable voltage drop across the component is 0.5v and the total turned out to be 1.48v, almost 3 times that value.
The starter motor current draw to be tested using a clamp meter. The specified current draw is 125-150 amps. The test result was 133A which is a pass.
REPORT:
The voltage drop showed increased figures than specified which means there is resistance within the circuitfrom the battery to the starter motor and within the solenoid. Amps however were within specified range. The resistance source needs to be minimised for starter motor efficiency.
Starter circuit test failed.
Starter Motor Bench Testing and Repair
3 March 2011
In our group we had a Mitsubishi starter motor (Model Number M3T 49381) to pull apart and test various components to see if it was all working correctly. (All multimeter reading were measured using a 200ohms scale.)
The booklets we were given had a basic summary of all the tests we were about to perform, the possible results and why this would be so that we were actually understanding what we were doing.
To start, we did a no load test on the starter motor to make sure that the solenoid was operating. The result of this test was 11.5v and 35.2A. We then followed a strict procedure to dismantle the motor, marking sections so they could be realigned when put back together.
Armature:
First, the Visual Inspection, we checked the armature for any possible signs of overheating, burning, physical damage or poling. There were no real major visual signs of distress, only minor scratches on the plates which still means that the armature was serviceable. We then performed a ground circuit test, placing one of the meter leads on the armature core and the other lead on between each of the commutator segments. This should read infinity as there shoul be no circuit. As this passed, it shows that the armature is serviceable. We then had to test the continuity of the armature by placing one probe on the commutator and moving the other around the commutator (not breaking contact) to see how much resistance is within the circuit. The result of this was 0 ohms which is within recommended specifications and is therefore still serviceable. Then we had to measure the diameter of the commutator and the mica undercut depth. The diameter of the commutator that we were working with, was 20.05mm which is below manufacturers specifications of minimum diameter (26.8mm - 31mm). Therefore in this regard it failed and was not serviceable, however, it was explained that the specifications were perhaps not for the particular model that we were working with. Also the mica undercut was suggested to be 0.7mm - 1mm, it was said that the measurement of this was impractical and to make an estimation of depth. The armature was then to be placed "V" blocks to perform a dial test to check for run out. The armature had to be turned 360 degrees to get an acurate reading. The specifications for this were 0mm - 0.2mm. Our test came back with 0.05mm and therefore is serviceable.
We then used an alternative method of testing the armature using a 48 volt test light, to test continuity and ground. For the continuity test, it is performed the same way but on the machine, this test applies greater pressure to the windings and should be used where avaliable, the light on the test glowed, which means that the continuity of the circuit was good and still serviceable. For the ground test, it is also performed the same way, but in this instance the light will stay off to show theere is no circuit, this means it is still serviceable.
Also, to test for short circuits in the armature, it is placed on the "V" of the growler and switched on. A hacksaw blade is held loosely on top of the armature, the blade did not vibrate which means that there are no short circuits.
Field Coil and Pole shoes:
First, the visual inspection, where we checked for and visible signs of overheating, burning, physical damage or poling. Again, no major visual faults, only minor such as covering of wires tearing slightly, and coil wires becoming loose and frayed. This means that it was still serviceable.
We then checked the fied coils for continuity, but first we had to check the internal resistance of the meter itself which turned out to be 0.4 ohms. We were given 2 options on the worksheet 'If Grounded' (specifications - Test N/A) or 'Not Grounded' (specifications - 0-0.02 ohms). The results of my test turned out with just the internal resistance of the meter, so there for the test was N/A, meaning it was grounded and serviceable. To then check if the field coils were grounded we had to place a positive probe on the field wire or brush, then the common probe on the body of the starter. Again, given the same 2 options 'If Grounded' (specifications 0-0.02 ohms) and 'Not Grounded' (specifications Infinity), and being that our meter read infinity means that the component is still serviceable.
The length of the brushes had to be measured with the vernier calliper and specified to be longer than 5mm. Also, we had to check for cracks or other damage of the brushes. There was no visible damage to the brushes and results showed the 2 brushes were 5mm each which passed. The brushes also needed to be checked for short circuits between insulated brushes. This is achieved by placing one probe on the brush and the other on the metal retaining plate. The result of this test showed infinity which means that the holder is insulated and it passes to remain serviceable.
Solenoid Magnetic Switch:
We first had to identify the terminals. The battery terminal of the solenoid is obvious as it is isolated from the rest, the starter motor supply is also obvious as it lead from the solenoid into the starter, therefore leaving the remaining terminal to be the ignition/starter switch supply. We then checked that the pull in windings of the solenoid were working by connecting a 9v power supply to the ignition terminal and the starter motor supply terminal. This is only applied for 5 seconds to prevent heat damage to the windings. The maufacturers specifications of the current draw of these windings should be 8-12 amps, the pull in windings of ours however had a current draw of 23A which is too much current to be activating the windings. When they are activated however, the plunger of the solenoid should be pulled in which it did. ALso in the solenoid are hold in windings which are activated after the plunger is pulled in to hold it in place. This time, the 9v power supply is connected to the ignition terminal and the solenoid body. The plunger must be pushed in by hand and released to see if it is held in place. The current draw of this should be 5-8 amps. The result was 7A which passes.
Pinion Gear and Overrunning or One Way Clutch:
This needs to be inspected for damage and smooth movement along the shaft. The bushes must be checked for wear and also the bush clearance in the appropriate end housong. Each were in good condition and serviceable.
The starter motor then had to be reassembled, housing realligned to marks made. However, when we were putting the component back together, the frayed wiring of the field coil terminals became increasingly worse and one of the terminals snapped off completely. It was suggested that we continue to put it together without that terminal and complete a no load test to see if it would still work.
The final no load test was unable to be performed and the starter motor was unable to perform.
REPORT:
The initial no load test carried out gave results showing the starter was within manufacturers specifications. However, once taken apart it became apparent that the brush wires were frayed and therefore the brush came off completely causing the circuit to be incomplete. When final no load test was carried out after re-assembly of starter, the results were unavaliable as the windings within the solenoid were not able to generate anything. I would recommend changing/replacing brush holders.
In our group we had a Mitsubishi starter motor (Model Number M3T 49381) to pull apart and test various components to see if it was all working correctly. (All multimeter reading were measured using a 200ohms scale.)
The booklets we were given had a basic summary of all the tests we were about to perform, the possible results and why this would be so that we were actually understanding what we were doing.
To start, we did a no load test on the starter motor to make sure that the solenoid was operating. The result of this test was 11.5v and 35.2A. We then followed a strict procedure to dismantle the motor, marking sections so they could be realigned when put back together.
Armature:
First, the Visual Inspection, we checked the armature for any possible signs of overheating, burning, physical damage or poling. There were no real major visual signs of distress, only minor scratches on the plates which still means that the armature was serviceable. We then performed a ground circuit test, placing one of the meter leads on the armature core and the other lead on between each of the commutator segments. This should read infinity as there shoul be no circuit. As this passed, it shows that the armature is serviceable. We then had to test the continuity of the armature by placing one probe on the commutator and moving the other around the commutator (not breaking contact) to see how much resistance is within the circuit. The result of this was 0 ohms which is within recommended specifications and is therefore still serviceable. Then we had to measure the diameter of the commutator and the mica undercut depth. The diameter of the commutator that we were working with, was 20.05mm which is below manufacturers specifications of minimum diameter (26.8mm - 31mm). Therefore in this regard it failed and was not serviceable, however, it was explained that the specifications were perhaps not for the particular model that we were working with. Also the mica undercut was suggested to be 0.7mm - 1mm, it was said that the measurement of this was impractical and to make an estimation of depth. The armature was then to be placed "V" blocks to perform a dial test to check for run out. The armature had to be turned 360 degrees to get an acurate reading. The specifications for this were 0mm - 0.2mm. Our test came back with 0.05mm and therefore is serviceable.
We then used an alternative method of testing the armature using a 48 volt test light, to test continuity and ground. For the continuity test, it is performed the same way but on the machine, this test applies greater pressure to the windings and should be used where avaliable, the light on the test glowed, which means that the continuity of the circuit was good and still serviceable. For the ground test, it is also performed the same way, but in this instance the light will stay off to show theere is no circuit, this means it is still serviceable.
Also, to test for short circuits in the armature, it is placed on the "V" of the growler and switched on. A hacksaw blade is held loosely on top of the armature, the blade did not vibrate which means that there are no short circuits.
Field Coil and Pole shoes:
First, the visual inspection, where we checked for and visible signs of overheating, burning, physical damage or poling. Again, no major visual faults, only minor such as covering of wires tearing slightly, and coil wires becoming loose and frayed. This means that it was still serviceable.
We then checked the fied coils for continuity, but first we had to check the internal resistance of the meter itself which turned out to be 0.4 ohms. We were given 2 options on the worksheet 'If Grounded' (specifications - Test N/A) or 'Not Grounded' (specifications - 0-0.02 ohms). The results of my test turned out with just the internal resistance of the meter, so there for the test was N/A, meaning it was grounded and serviceable. To then check if the field coils were grounded we had to place a positive probe on the field wire or brush, then the common probe on the body of the starter. Again, given the same 2 options 'If Grounded' (specifications 0-0.02 ohms) and 'Not Grounded' (specifications Infinity), and being that our meter read infinity means that the component is still serviceable.
The length of the brushes had to be measured with the vernier calliper and specified to be longer than 5mm. Also, we had to check for cracks or other damage of the brushes. There was no visible damage to the brushes and results showed the 2 brushes were 5mm each which passed. The brushes also needed to be checked for short circuits between insulated brushes. This is achieved by placing one probe on the brush and the other on the metal retaining plate. The result of this test showed infinity which means that the holder is insulated and it passes to remain serviceable.
Solenoid Magnetic Switch:
We first had to identify the terminals. The battery terminal of the solenoid is obvious as it is isolated from the rest, the starter motor supply is also obvious as it lead from the solenoid into the starter, therefore leaving the remaining terminal to be the ignition/starter switch supply. We then checked that the pull in windings of the solenoid were working by connecting a 9v power supply to the ignition terminal and the starter motor supply terminal. This is only applied for 5 seconds to prevent heat damage to the windings. The maufacturers specifications of the current draw of these windings should be 8-12 amps, the pull in windings of ours however had a current draw of 23A which is too much current to be activating the windings. When they are activated however, the plunger of the solenoid should be pulled in which it did. ALso in the solenoid are hold in windings which are activated after the plunger is pulled in to hold it in place. This time, the 9v power supply is connected to the ignition terminal and the solenoid body. The plunger must be pushed in by hand and released to see if it is held in place. The current draw of this should be 5-8 amps. The result was 7A which passes.
Pinion Gear and Overrunning or One Way Clutch:
This needs to be inspected for damage and smooth movement along the shaft. The bushes must be checked for wear and also the bush clearance in the appropriate end housong. Each were in good condition and serviceable.
The starter motor then had to be reassembled, housing realligned to marks made. However, when we were putting the component back together, the frayed wiring of the field coil terminals became increasingly worse and one of the terminals snapped off completely. It was suggested that we continue to put it together without that terminal and complete a no load test to see if it would still work.
The final no load test was unable to be performed and the starter motor was unable to perform.
REPORT:
The initial no load test carried out gave results showing the starter was within manufacturers specifications. However, once taken apart it became apparent that the brush wires were frayed and therefore the brush came off completely causing the circuit to be incomplete. When final no load test was carried out after re-assembly of starter, the results were unavaliable as the windings within the solenoid were not able to generate anything. I would recommend changing/replacing brush holders.
Alternator Off Car Testing
In this exercise we had to dismantle an alternator and carry out different tests to see if the alternator was working properly and if not, what component would be the source of this failure.
Following the given list of instructions in the booklet, we took apart the alternator and began testing.
Starting on the Rotor windings, we tested it to ground. (Multimeter set to 2K on ohms scale.) To do this, we placed the black lead from the multimeter on on the centre of the rotor shaft and the red lead on the slip ring. The meter should end up with no reading. Also, the rotor winding internal resistance is tested. For this the leads are to be placed on the slip rings. The meter should read between 2-6 volts as specified. The reading achieved was 3.2 (minus the internal resistance of the multimeter) which gives a final result of 2.8 ohms. Results of these tests are within specs and pass.
Then further opening the alternator, the stator winding resistance is tested. This is achieved by placing the black lead of the meter on the common terminal (terminal with the most wires leading to it) and the red on each of the other terminals to gain readings of each. The spec for this was to be between 0 - 2 ohms. 0.2, 0.1 &0.1 were the readings of the terminals which makes them within specifications and therefore also pass. Then to make sure that the common terminal is grounded, the black lead is placed on the body of the alternator whilst the red is on the common terminal. To pass, there will be no reading on the meter. This was the case which means that there is no circuit between the stator winding and ground.
The meter then needs to be chnaged to diode test mode to test the rectifier positive diodes. Testing each of these, Black lead on a common terminal and the red on each of the rest one at a time. There were 3 terminals which gave relatively similar readings (0.580, 0.590, 0.579) and the other gave no rading at all. This is so as one of these terminals is the common ground and as such should have no circuit. Therefore all of these passed. This test is then reversed and all results should read infinity (no reading at all). All results were as required.
Testing the rectifier negative diodes is slightly different as the red lead is placed on a body terminal and the black is placed on each of the 4 other terminals one at a time. The results were the same however.
Testing the voltage regulator, we first had to find out the make of it, this was done (personally) by comparing the regulator to the diagrams in the booklet and finding a match. Carrying out a Transpo regulator test, we had to make sure the short circuit light was of (Pass), The warning light came on and stayed on (Pass), the field light should flash continuosly (Pass) and the reading (12.5v) was what it needed to be (Pass). This means that the regualtor is not short circuited and is doing its job correctly.
Then using a vernier caliper we checked the length of the brush protrusion. This is very important as if they are too short the brush springs can not apply enough pressure to maintain contact and in turn reduces output of the alternator. The length we got was 10.2mm and 10mm. This means it was well above the minimum length of 4mm.
REPORT:
Overall, the alternator passed, meaning that it operates as its supposed to and each component is working well.
Testing the rotor winding internal resistance gave a measurement of 2.8 ohms which is between recommended specifications of 2 and 6 ohms. Being that the rotor is an electromagnet if resistance is too high, this causes the magnetic field to become weaker which in turn decreases the field current of the circuit. If this happens the voltage regulator will have less field current to adapt to constant voltage at the stator output. This will also reduce the field current that will be induced into the stator windings and therefore have less output to the terminals of the coils with the same result of rectifier which will draw more energy from the battery to compensate for the fault, greatly decreasing the battery's state of charge over time.
It is very important that the rotor winding internal resistance is between specified values, if not they may need to be replaced.
Following the given list of instructions in the booklet, we took apart the alternator and began testing.
Starting on the Rotor windings, we tested it to ground. (Multimeter set to 2K on ohms scale.) To do this, we placed the black lead from the multimeter on on the centre of the rotor shaft and the red lead on the slip ring. The meter should end up with no reading. Also, the rotor winding internal resistance is tested. For this the leads are to be placed on the slip rings. The meter should read between 2-6 volts as specified. The reading achieved was 3.2 (minus the internal resistance of the multimeter) which gives a final result of 2.8 ohms. Results of these tests are within specs and pass.
Testing the rectifier negative diodes is slightly different as the red lead is placed on a body terminal and the black is placed on each of the 4 other terminals one at a time. The results were the same however.
Then using a vernier caliper we checked the length of the brush protrusion. This is very important as if they are too short the brush springs can not apply enough pressure to maintain contact and in turn reduces output of the alternator. The length we got was 10.2mm and 10mm. This means it was well above the minimum length of 4mm.
REPORT:
Overall, the alternator passed, meaning that it operates as its supposed to and each component is working well.
Testing the rotor winding internal resistance gave a measurement of 2.8 ohms which is between recommended specifications of 2 and 6 ohms. Being that the rotor is an electromagnet if resistance is too high, this causes the magnetic field to become weaker which in turn decreases the field current of the circuit. If this happens the voltage regulator will have less field current to adapt to constant voltage at the stator output. This will also reduce the field current that will be induced into the stator windings and therefore have less output to the terminals of the coils with the same result of rectifier which will draw more energy from the battery to compensate for the fault, greatly decreasing the battery's state of charge over time.
It is very important that the rotor winding internal resistance is between specified values, if not they may need to be replaced.
Tuesday, 19 April 2011
Battery Testing
We were in pairs and had been assigned a battery for each pair. We were told and shown how to test the battery and had to work our way through the practical booklet we were given.
The battery Thomas and I were assigned was a Lucas conventional type battery with a 410 CCA rating. The battery number of which was 46G.
The first thing to do when testing any battery is to carry out visual checks. This consists of, battery terminals, surface, possible swelling of the battery etc. From this check it seemed as if the battery termials were clean and tight, there was no swelling of the battery evident. However, there was minor fluid apparent on the surface of the battery around the cells which could indicate leakage. Recommended further inspection.
We then had to remove the cell covers to check the electrolyte levels of each cell. Apparently if they are at the appropriate level, you will barely be able to see the cells at first glance as they will be covered by the electrolyte, however the level must not be too high. All our electrolyte levels appeared to be okay.
We then had to perform a battery open circuit voltage test. In this test it is important that surface charge is removed as it can give false readings. This can be achieved by turning on the headlights for approx 1-2 mins. When they are turned off the meter reading will drop and then build itself back up, where it stops is the reading needed. (The meter needs to be set to 20 DC volts) The result of this was 12.7v, which meant the state of charge on our battery was 100%. The battery must be over 50% charged before any other testing could be performed which meant ours was fine as it was over 12.4v. If it is lower than 50%, it must be charger slowly so as not to over exert itself.
As our battery was sufficient to continue testing we then began to test the specific gravity of the electrolyte. When this test is performed it is important that whoever is doing this test is wearing safety glasses and gloves as the electrolyte is an acid. Each cell needs to be tested individually with a hydrometer. This creates a vacuum which pulls the electrolyte into the hydrometer and makes the float float. First the fluid needs to be checked, if it is clear or murky. Then the reading, the variations of each of these cells should be no more than 50. In this regard our battery failed as our readings were: Cell 1: 1305; Cell 2: 1295; Cell 3: 1300; Cell 4: 1300; Cell 5: 1295; Cell 6: 1250. The specific gravity variation of this battery was 55.
We then carried out a high rate discharge test, using a load tester. The positive clip to be attached to the positive terminal and the negative to the earth terminal. This gave the load tester power. We then had to dial the amp on the load tester to half of the CCA rating which in this case was 205A. As it reaches the desired voltage, we must watch the voltage meter. The load should be held at 9.5v or over. Our battery held at 10.1v which means it was capable of holding its necessary load and is working.
When the engine is off, there are often things in a vehicle that can draw power from the battery. These at any given time should not be above 0.03Mv. If it is any more than this it will cause the battery to die very quickly. This is tested by adding an ammeter to the circuit as one of the components. (Series). Negative to negative terminal, positive to negative wire now unattached. The result of this test was 0 as we were working on engines off car, therefore there was no radio memory or anything to draw from the battery.
Report:
I recommend the battery terminals be cleaned as when the connection was removed for the draw test there was minor corrosion. This to be cleaned with hot water and baking soda until gone and then sealed with grease or petroleum jelly.
If the battery needed charging it should be done with a battery charger on slow charge.
If the amp draw were too high on the battery, the problem would be easily tracked down by keeping the circuit avaliable but removing possible draws until the amp drops. This would show what is drawing too much current while the engine is off.
When testing with a digital meter, it will simply tell you if your battery is pass or fail. The meter needs to be set to SAE and the CCA rating set. To test, the test button should be pressed and the screen will show a pass or fail. Our meter told us our battery failed which means that the battery needs to be replaced. Then press test button again to get O.C.V which was said to be 12.91v. From these results i would recommend cleaning the battery terminals and retesting in case corrosion caused false results. If it fails again, dispose of the battery.
The battery Thomas and I were assigned was a Lucas conventional type battery with a 410 CCA rating. The battery number of which was 46G.
The first thing to do when testing any battery is to carry out visual checks. This consists of, battery terminals, surface, possible swelling of the battery etc. From this check it seemed as if the battery termials were clean and tight, there was no swelling of the battery evident. However, there was minor fluid apparent on the surface of the battery around the cells which could indicate leakage. Recommended further inspection.
We then had to remove the cell covers to check the electrolyte levels of each cell. Apparently if they are at the appropriate level, you will barely be able to see the cells at first glance as they will be covered by the electrolyte, however the level must not be too high. All our electrolyte levels appeared to be okay.
We then had to perform a battery open circuit voltage test. In this test it is important that surface charge is removed as it can give false readings. This can be achieved by turning on the headlights for approx 1-2 mins. When they are turned off the meter reading will drop and then build itself back up, where it stops is the reading needed. (The meter needs to be set to 20 DC volts) The result of this was 12.7v, which meant the state of charge on our battery was 100%. The battery must be over 50% charged before any other testing could be performed which meant ours was fine as it was over 12.4v. If it is lower than 50%, it must be charger slowly so as not to over exert itself.
As our battery was sufficient to continue testing we then began to test the specific gravity of the electrolyte. When this test is performed it is important that whoever is doing this test is wearing safety glasses and gloves as the electrolyte is an acid. Each cell needs to be tested individually with a hydrometer. This creates a vacuum which pulls the electrolyte into the hydrometer and makes the float float. First the fluid needs to be checked, if it is clear or murky. Then the reading, the variations of each of these cells should be no more than 50. In this regard our battery failed as our readings were: Cell 1: 1305; Cell 2: 1295; Cell 3: 1300; Cell 4: 1300; Cell 5: 1295; Cell 6: 1250. The specific gravity variation of this battery was 55.
We then carried out a high rate discharge test, using a load tester. The positive clip to be attached to the positive terminal and the negative to the earth terminal. This gave the load tester power. We then had to dial the amp on the load tester to half of the CCA rating which in this case was 205A. As it reaches the desired voltage, we must watch the voltage meter. The load should be held at 9.5v or over. Our battery held at 10.1v which means it was capable of holding its necessary load and is working.
When the engine is off, there are often things in a vehicle that can draw power from the battery. These at any given time should not be above 0.03Mv. If it is any more than this it will cause the battery to die very quickly. This is tested by adding an ammeter to the circuit as one of the components. (Series). Negative to negative terminal, positive to negative wire now unattached. The result of this test was 0 as we were working on engines off car, therefore there was no radio memory or anything to draw from the battery.
Report:
I recommend the battery terminals be cleaned as when the connection was removed for the draw test there was minor corrosion. This to be cleaned with hot water and baking soda until gone and then sealed with grease or petroleum jelly.
If the battery needed charging it should be done with a battery charger on slow charge.
If the amp draw were too high on the battery, the problem would be easily tracked down by keeping the circuit avaliable but removing possible draws until the amp drops. This would show what is drawing too much current while the engine is off.
When testing with a digital meter, it will simply tell you if your battery is pass or fail. The meter needs to be set to SAE and the CCA rating set. To test, the test button should be pressed and the screen will show a pass or fail. Our meter told us our battery failed which means that the battery needs to be replaced. Then press test button again to get O.C.V which was said to be 12.91v. From these results i would recommend cleaning the battery terminals and retesting in case corrosion caused false results. If it fails again, dispose of the battery.
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