Resistors and Relays

Resistors:

We started off resistors by calculating values of different resistors. An example of this was a resistor with the colours red, red, orange and gold. The first red is a 2, as is the second. So we have 22. the orange means multiply by 1000, so we now have 22000Ω and the gold means a 5% tolerance. Measuring this on the multimeter, we got a reading of 21800Ω.

Next we got two resistors of 98.6Ω and 813Ω. We put these two resistors in series and got a reading of 910Ω. We then put the two in parallel and got a reading of 88Ω.

When 2 resistors are placed in series, the total resistance is the sum of the two, therefore the total resistance will be higher than the highest.

When they are in parallel, the inverses of the values are added up, then the inverse of that value is taken to get the total resistance. This value will be lower than the value of the lowest resistor.

Relays:

To start off relays, we measured the resistance through the different terminals. 86 to 85 had 75Ω of resistance due to the windings. 30 to 87a had no resistance because it is straight through a switch, and 30 ro 87 read infinity because it is an open circuit. The control circuit trminals are 86 and 85 and the switch circuit terminals are 30, 87a, and 87. We then calculated how much current would flow through the control circuit if 12v was supplied by using the formula I=V/R which equals 12/75 which equals .16A. The switch circuit that is normally open is from terminal 30 to 37a and the switch circuit that is normally open is from terminal 30 to 87.

We then set up a circuit that involved a switch, fuse, 5 pin relay, and 3 bulbs which come from the switch/consumer circuit of the relay. We performed multiple voltage available tests with the circuit on and off. We found that the voltage changed the most at terminals 85, 87a, and 87. This was due to the valtage drop in the windings and the switch changing position respectively.

-There is no change in the voltage at terminal 86 because this is the input of the control circuit of the relay.

-At terminal 85, the available voltage while the circuit was off was full supply voltage, but when the circuit was switched on, the available voltage was zero, because it was used up through the windings to create the magnetism.

-There is no change in voltage at terminal 30 because this is the main input to the switched circuit and is connected directly to the battery.

-At 87a, there is full voltage because the switch is normally closed, so there will always be full voltage here in the normally closed position. When the circuit was switched on, the voltage became zero because the switch had switched over.

-At 87, there is no voltage available because the switch is normally closed so the switch was not connected to this terminal. When the switch was switched on, the switched moved across to terminal 87 so there was full voltage.

 The final part of relays was to make a circuit to switch between 2 light bulbs. We did this by connecting one light bulb to terminal 87a, and another to 87. So when the switch was changed over, it went from one light bulb to the other.

Diodes

Diodes are important as they only allow current to flow in one direction and are used in places like rectifiers on an alternator.
The first test we did was to measure the resistance of the diode using the 2k setting on the ohm meter. The meter read infinity because the ohm meter does not put out enough voltage to break through the bindery layer of the diode. We then tested the diode using the diode test position on the multimeter. We got a reading of infinity from the cathode to anode position, and .54v from the anode to cathode position which means it it needs .54v to break through the diode.
Next we set up a small circuit using a 12v power supply, a 1kΩ resistor, and a diode. The resistor had a voltage drop of 12.71v, and the diode had a voltage drop of .66v. The diode should not have a big voltage drop because it is not a consumer. The voltage drops add to 13.37v and the available supply voltage was 13.37v. The current flow at the diode measured .013A.
In a series circuit, the voltage drops of each consumer should add to the total supply voltage.
The next test was the same, except we used a bigger resistor, a 9.89kΩ resistor.
Voltage drop across the resistor didnt change a huge amount, but was slightly bigger at 12.81v and .56v across the diode. The current flow however was alot lower at .001A
Because we have a bigger resistor, there was a higher voltage drop and less current.
In the next part of the test we used a light emmiting diode, instead of a normal diode and a 1kΩ resistor. Using the diode tester, we found the LED needs 1.95v to break through it. In doing this we found that the voltage drop of a LED is higher than that of a normal diode.
We found the voltage drop of the resistor was 9.04v and the voltage drop of the LED was 4.3v. The sum of the voltage drops is 13.34v and the available supply voltage was 13.35v. The current flow of the LED was .01A.
In the diode circuit, the diode doesn't use much voltage, therefore the resistor uses more. In the LED circuit, the LED uses mor voltage than the diode, so the resistor doesn't use as much.

Starter Motor bench testing report

Part of  4841 electrical is starting systems. In which we disassembled a starter motor, did a number of tests, and then reassembled it.
The first test we did was a no load test on the starter motor using the bench tester. Voltage read 12.8 volts and current read 38.8A which is normal. After we disassembled the starter, we did a ground circuit test between each commutator segment and the armature shaft. We got readings of infinity which means it is an open circuit, which means it is not grounding to the shaft, which is a pass. Next was a continuity test between each commutator segment. We got readings of 0 ohms on the ohm meter which means there is a circuit, but no resistance, which is a pass. We then tested the commutator diameter and undercut, these were both passes. We then checked the commutator diameter for its circle shape using the dial test indicator, this was in good order.
We then did a test for internal short circuits in the armature using the growler. The hacksaw blade did not vibrate at all so this was a pass.
We then did a visual inspection of the field coil and pole shoes. There were no signs of overheating, burning, physical damage or poling that could cause the starter motor to malfunction, so this was a pass.
We then tested the field coils for continuity. We got a reading of .02 ohms, which means there is a circuit with minimal resistance, which is a pass. Next we tested the field coils for grounding. We got a reading of infinity, which means it is a open circuit and the field coils are not grounding to earth, which is a pass.
We then checked the length of the brushes. All four were 15 to 16mm long which means they all make suitable contact with the commutator, which is a pass. We then tested the solenoid. The first part was the pull in windings. By connecting the power supply to the S and M terminals, the physical action was to pull in the plunger. It did this and drew a current of 20A. We found this to be higher than spec, but after other groups getting the same result, we concluded this to be normal for that type of solenoid. We then tested the hold in windings test. By connecting the power supply to the S terminal and body of the solenoid, it should hold the plunger in. It did this and drew 8A of current, which is in spec, which is a pass. It takes 20A to pull the plunger in and only 8A to hold it in, because it is easier to hold it in that pull it in.
The pinion clutch and bushes were all in good order so these were also passes.
We then reassembled the starter motor, before perfoming another no load test. We found it used 13.2V and 37A which is a pass.

Logic Probe

As part of the electrical course, we were to construct a logic probe. After constructing it, we were to answer a set of questions.

Q1: Why do both the red LED and the green LED go when you connect it to the battery?

A: The current flows through the green LED, through the brass rod, through the red LED and back to negative to complete the circuit.

Q2: Why does the green LED go out when the probe contacts the battery positive?

A: The green LED goes out because when the probe touches the positive, that makes the brass rod positve and the green LED shorts out. This is because the current coming from the positive alligator clip meets the (now) positive brass rod and has no where to earth.

Q3: Why does the red LED get brighter when the probe contacts the battery positive?

A: The red LED gets brighter because all of the current flows through the one LED and it gets all of the available voltage. The current flows from positive, through the probe, through the red LED and back to negative, not through the green LED.

Battery Testing

The first part of battery testing was inspecting for battery specifications. The make of our battery was a Lucas, battery number was 128HD. It has a Cold Cranking Ampere (CCA) of 400. It was a conventional battery and the electrolyte was easily accessable by removing the caps and using the tip of the hyrometer to check the level of the electrolyte.

We carried out visual checks and found that the terminals were clean and tight, there was no signs of swelling caused by overcharging.

In case of an accident, the nearest supply of water had to be identified, and was behind us about 2 meters away.

Next we had to check the electrolyte levels. To do this we dipped the hydrometer in until the tip touched the plates. We then removed it and the level can be seen on the rubber tip. The level was about 10 to 12mm above the plates. This was a bit high as the recomended level is 4 to 5mm above the plates.

The next test was to measure the open circuit voltage. With the meter range set on 20V, we got a result of 6.61v, which was due to the battery not being charged. The state of charge was recorded as under 25%.

To continue with the testing, we needed a state of charge of at least 50%, which equates to 12.4v, so our action was to put the battery on charge.

Using another battery, we got a set of hydrometer results. These results had a specific gravity variation of 100 points. The allowable specific gravity variation of a battery is between 25 and 50 points, so the result we got was a fail.

Next was to do a high rate discharge test, using a carbon pile. This was a different battery with a CCA of 310A. The load that we were to apply was 155A and the voltage that had to be held while the load was being applied is 9.5v. Our result was that the battery held a voltage of 10.6v while the loaad was being applied.

Next we used a digital battery tester to test the battery. The tester gave a reading of "PASS" which means the battery has adequate charge. The tester also said that the battery had and OCV of 13.46v. It also displayed a CCA reading of 300. The state of charge of the battery was 100%

The battery was in good condition. Although there was a surface charge on it, so putting a load on the battery for a short amount of time would have been appropriate.

Alternators - On car testing

Before we start testing the alternator, we need to carry out visual checks. This includes the connections, mountings, and tension of the drive belt. All of these were good.
The first tests that we do are no load tests, which means that there are no lights or other accessories on that will be causing the alternator to work harder.
The first test was the base battery voltage. This measured 12.42v, which is less than the 12.6v it should be.
The next test was the regulator voltage. It shoul have read between 14.5 and 14.6v. I measured 12.11v which is a fair bit less than it should be.
Finally with the no load tests was the amperage output. The carburetted output specification is between 5 and 12amps and I got a reading of .1A. I figured this was because the battery was fully charged and did not require charging from the battery. So I switched off the engine and let the fan run for a few minutes to drain the battery. I tried again and still only found that the output was .1A so I came to the conclusion that the alternator is at fault.
Next was to carry out a load test on the alternator. Since we only have have an engine, we cannot put a load on it using the accessories of a car, so we have to use a carbon pile to create a load.
since I found my alternator was not working properly, I joined the group next to me and found the output amps under load to be 29.1A and the charging voltage under load to be 12v.
The final tests were voltage drop tests. The first one was between the battery positve post and the output of the alternator. The voltage drop should be less than .2v, we measured .13v, so this is a pass. This is showing us if there is a drop in voltage from the alternator to the battery.
The second test was between the battery negative post and the body of the alternator. This should have also read less than .2v and ours read .16v which is a pass, so this is also a pass. This is showing us if there is a voltage drop through the earth part of the circuit.

Alternators - Off car testing report.

After we removed the rear cover, the regulator and the brush holder on the alternator, we were able to carry out tests for the rotor winding to ground and the rotor winding internal resistance test. In the rotor winding to ground test, we are testing to see if there is a circuit butween the rotor shaft and the slip ring. There should not be a circuit here and the meter should read infinity, when the meter is set to 2k. If there is a circuit here, it means the rotor winding is shorting to earth, and will need to be replaced.
On the rotor winding internal resistance test, we are testing to see if there is a circuit between the two slip rings. There should be a circuit between the two rings, and with the ohms meter set to 200ohms, we should get a reading between 2 and 6 ohms. In my test we got 3 ohms which is a pass. The ohms meter did not have any internal resistance I did not have to subtract it from the reading. If there is no circuit between the slip rings, they need to be replaced.
To carry out the next tests, I had to remove the rectifier, and the housing of the alternator so that we could access the stator winding terminals. We tested the internal resistance in these by connecting the negative of the meter to the common stator winding terminal. The specifications of the resistance should be between 0 and .2 ohms. I tested them all and found they had a resistance of .2 ohms each which is a pass.
The next test was the stator winding to ground test. This is where we test to see if there is a circuit between the stator winding and ground. We test this by connecting the positve of the meter to the common stator terminal and the negative of the meter to the body of the alternator. There should not be a circuit here so the meter, set on 2k, should read infinity. My test read infinity so that is a pass.
Next we tested the rectifier positive diodes. The rectifier is what turns the AC current produced by the alternator into DC current. To do this we put the negative lead onto the main terminal and then the positive lead onto each of the four p-terminals. The readings for the meter should be between .5 and .7VD My readings were between .491 and .497, so that is a fail. The next test we put the positive lead onto the main terminal and the negative lead on the p-terminals. The meter should now read infinity, and it did so that is a pass.

The next test was to test the rectifier negative diodes. To do this we set the meter to diode test mode. The negative lead gets put onto the E terminal and the positive lead onto each of the p terminals. The meter should read infinity, which it did, so that was a pass. The positive lead was then put onto the E terminal, with the negative lead onto each of the p terminals. The meter should have read between .5 and  .7VD. I got readings between .485 and .492, which are all fails.
The next test was to test the voltage regulator. The regulator controls how much current and voltage is sent away from the alternator. To test a regulator, we used a device called the Transpo Voltage Regulator Tester. After testing the regulator, I found that the set point voltage of the regulator was 12.1v, which does not meet the specification of 14.5v, so this tells us that the regulator needs to be replaced.
The bearing should also be replaced when servicing an alternator. The bearing is what allows the rotor shaft to spin. It turned smoothly and without any resistance.

The final check was to check the protrusion length of the brushes. On the brushes that I pulled of the alternater, the brushes were so worn that they popped out of the holder. I found new brushes and measured the protrusion length of these ones. The first brush measured 10.5mm and the second measured 11.5mm. The minimum length is 4mm, so these were both passes.