Capacitors

Capacitors are electronic devices used to store electrical charge and prevent voltage spike. The negative plate provides a form of reservoir into which electron can flow and this stores any excess of voltage. It is measured in Farad.

The capacitor will discharge almost instantly, but to charge up need a bit time. However majority of it charge capacity will be charged up very quickly. As capacitor is getting more charged up it becomes hard because the capacity is nearly filled up with charges, this is why it take even longer to charge this remaining portion.

Time needed for a capacitor to get fully charge can be calculate with the formula below

T = 5RC

T is the time takes to fully charge a capacitor

5 is a constant

R is the resistance that connect in series with a capacitor to control the charging rate

C is the capacitance of the capacitor

In this lab we want to fully charge a 16V 330uF capacitor in 180secs

Above formula is used to calculate the resistor needed to control the charge up time

R = T / (5C)

T = 180s

C= 0.0033F

R=180/5(0.0033) = 10kohm

I connect this capacitor in series with 10kohm resistor in series with a supply voltage of 13.31V. I discharged the capacitor by connecting its leads with a jumper wire then removed the jumper wire to let it charge up and recorded the following voltages with 10 seconds interval for 180 seconds:

10s     7V	20 s     12V	30s  13.25V	40s   13.2 V	50s   13.2 V	60 s  13.29 V
70s  13.30V	80s  13.30 V	90s  13.30 V	100s 13.30 V	110s 13.30 V	120 s 13.30 V
130s 13.30V	140s 13.30 V	150s 13.30V	160s 13.30V	170s 13.30 V	180 s 13.31 V

This shows this charging characteristic of a capacitor, it charges up very quickly in the begin and getting slower and slower to towards the end.

Resistors

Resistors

With resistors we learned how to read the color code of four band and five band resistors.

For example

A four bands resistor with brown, black, brown and brown it means

Brown      Black         Brown      Brown

1                0                10              1% tolerance

The resistance of this resistor is

10 X 10 Ohm +/- 1%  = 100 Ohm +/- 1%

A five bands resistor with brown, black, brown, brown and brown it means

Brown      Black         Brown      Brown      Brown

1                0                1                10              1% tolerance

101 X 10 Ohm +/- 1%  = 1010 Ohm +/- 1% = 1.01 kOhm +/- 1%

In series cct total resistance is

R_total = R₁ + R₂ +…+R_n

In parallel cct total resistance is

1/R_total = 1/R₁ + 1/R₂ + …+ 1/R_n

When connect resistors in series they add up to give a greater total resistance. In parallel cct the total resistance of the cct is decreasing as more resistors are connected in parallel.

Diodes

Diodes

Diodes are semi conductors, which are designed only allow current flow in one direction only normally. There are many types of diodes. In this topic we will only talk about simple diodes such as rectifier diodes.

They will conduct only in one direction only when the knee voltage is exceeded. Otherwise it won’t really conduct electricity. This knee voltage is normally quite low. This is why when we connect an ohm meter to a diode in its forward bias direction, the reading is over limit. The ohm meter could only output 0.24v, this is below the diode’s knee voltage. This diodes later tested with diodes test mode shows a knee voltage of 0.67. The output voltage of an ohm meter is measure by connecting to a voltmeter.

Anyway, once the knee voltage is reached in the forward bias direction diode will conducts with almost no resistance. Diode will not normally conducts in the reverse biased direction until its breakdown voltage is reach. Then obvious the diode is destroyed. Zener diode is an exception though.

In this lab we first connected a diode of 1.66V knee voltage in series with a 1kohm resistor. The supply voltage is 13.3V. We did the following measurements:

The V_drop of resistor                             13.14V

The V_drop of the diode                         0.66V

Amp flow through the diode             0.01A

The available supplied V                    13.82V

In this cct due diode’s low resistance in its forward bias, only very little V is used over the diode to push current through.

We then replaced the 1kohm resistor with a 10kohm resistor and got the following results:

The V_drop of resistor                             13.3V

The V_drop of the diode                         0.50V

Amp flow through the diode             0.001A

The voltage drop across the diode dropped below its knee voltage there is almost no current is flowing anymore. Perhaps this was an good example because 10kohm is already too high resistance for this cct.

Finally we replaced this diode with a LED and replaced the 10kohm resistor with a 1kohm resistor. The following is our test result:

The V_drop of resistor                             11.6V

The V_drop of the LED                                      2.1V

Amp flow through the diode             0.01A

The available supplied V                    13.82V

Compare with the very first cct. The LED required more Vdrop this is because it has a much high knee voltage before it will conduct in the forward b

Altenator

Alternator test

As in starter test this test is divided into two part

On car

Off car

Part one On car testing

Step 1

As usual did visual inspection to make sure battery is ok, connections and wiring are good, alternator is mounted in place firmly and there is no sign of damages. Also special care should taken to make sure that alternator belt is in good condition – no damages, cracks or contamination etc.

Everything is good condition apart from battery mounting as usual. Unitec seems couldn’t afford it.

Step 2

Removed surface charge and did an OCV test on the battery to make sure battery’s state of charge is at least 12.4V as in starter testing. If battery is not charged up to this level, there is not much point to continue our testing on the alternator because result will be misleading.

Battery OCV or the base voltage is 13.1V – 100% charged.

Step 3

Battery is ok, now let do a no load test to see if altenator is working. When engine started the battery voltage should increase at least 0.5V compare to the OCV or base voltage of the battery, therefore should give a reading of at least 13.6V.

Turn on the engine and put a voltmeter across battery terminals. The voltmeter gives a reading of 14.6V. This is well above minimum.

This test also shows us another important fact is that alternator’s voltage regulator is functioning properly. This 14.6V we just measured is also the alternator regulator voltage. Specification is between 13.5 and 14.5V, a little higher but I think it is ok. This test shows that alternator’s regulator is actually controlling output voltage. If the voltage goes too high such as above 15V or so low – the voltage regulator is probably faulty.

Step 4

Output amperage of the alternator should also be check. This is done with a clamp on amp meter, clamp around the positive cable directly connected to the battery terminal. This car showed a good reading of 5.5V where specification is 10 to 18A max. If the output amp is higher than specified then further test is needed to find out why. Amount of current flowing out the alternator is an indication of load. If there is no load then there shouldn’t have too much current.

Step 5

We see that this alternator is producing a good regulated voltage. Now we need to see that it could also provide enough current to the consumers under heavy load. This is called a load test. I attached a load tester to the battery terminals. While engine is running I use the load tester to applied 50A to the battery terminals. This alternator immediately responded to this load and increased it output amp from 5.5V to 68.8A while output voltage remaind at 14.2V.

Now we can say that this alternator is healthy. It is providing good regulated voltage and right amount current to the charging system.

Step 5

We know that the alternator is healthy, but we still need to make sure what coming out this alternator is going to get to the battery. Therefore we have to do 2 voltage drop tests to make sure it is connected to the battery properly from positive and negative side.

Voltage drop between altenator body and battery negative terminal is the negative path which give a reading of 0.06V. While specification is 0.2V.

Voltage drop between the alternator B terminal and positive terminal of the battery is the positive path gives a reading of 0.02. While specification is 0.2V.

The results show clearly that this alternator is properly connected to the battery through good path with low resistance.

Part two Off Car test

As with starter this test is only neccerray if we are certain problem is within the altenator.

Step 1

Dissemble alternator as instructed

Step 2

Make a visual inspection that nothing is obviously damaged and there is no strange smell.

Step 3

Check that there is no short between rotor winding and shaft by connecting ohm meter between slip ring and rotor shaft. Our result shows infinity. This shows that winding are not shorted to rotor shaft.

Step 4

Check there is no open circuit within the rotor winding. Connect ohm meter between slip rings. Meter reading is 2.8 ohm. Specification is 2-6ohm. The connectivity of the rotor winding is good.

Step 5

Check stator winding. Make sure there is no open cct in these three windings. Connect each terminal to the common terminal with ohm meter. Returned reading are all 0ohm. This shows that there is no open cct within stator windings.

Step 6

Check winding are not shorted to ground. Connect the ohm meter between the common terminal and the earth. Return reading is infinity. This shows that no winding is short to ground.

Step 7

Once we make sure windings are good. We can now test the rectifier. Rectifier are made of 6 diodes to convert ac to dc. Three positive and three negative. Use the diode test mode on the multimeter test positive diodes first. Make sure they conduct in one direction only. If any diode conduct in both direction or does not conduct at all, that diode or diodes are faulty needs to be replaced.

Use the meter to test from both directions. All positive diodes only conduct in one direction give a reading of 0.5V and the other direction with infinity. Do same thing with negative diode. Negative diodes give same result.

Well sound like our rectifier is in good condition.

Step 8

Rotor, stator and rectifier are all in good condition. Now lets test voltage regulator with a voltage regulator tester. Followed instruction and found the right setting for my regulator which is M3 126000 – 1190. This regulator use Field setting A, 12V and set point spec is 14.6v.

After we connect the regulator and switched on the tester the following result returned:

Short cct light is off  - there is no short cct in this regulator

Warning light is on – cct to warning light on the dash board is working

Field Light is flashing – Current flow into the rotor is controlled accordingly by regulate

Set Point Voltage is 14.6V – correct voltage as determined

All this information is just saying one thing this regulator is good.

Step 9

Before we reassemble the alternator. We need to measure the brush length to make sure it contacts the slip ring properly. Therefore correct amount of current flow into the rotor. Our measured length is 5mm which is still longer than specified 4mm. brushes are still serviceable.

In conclusion this alternater we are testing is in good condition.

Any way we took these alternators up stair and put them on test benches. We see how they actually changing their output current according to amount of load while maintained their output voltage quite stable all thanks to Ian.

Starter testing

Battery testing

Battery testing is one of the most important tests. Before the condition of battery is determined, starter and alternator tests can’t be performed correctly.

I used the following general testing procedure is listed below to test a Lucas 127MF battery with CCA rating of 410A:

1.         Visual inspection

2.         Check electrolytes level

3.         Check the state of charge of this battery by OCV or hydrometer testing

4.         Load test to determine whether this battery could hold at least 9.6V when large load is applied for about 15s.

Testing Result

Step 1	Visual inspection
Result	No corrosions, Oxidation, Physical damage of any form, Deformation is found. Terminals and plugs are clean and tight. Only thing need to mention is that this battery needs to be mounted.
Explanation	There is no sign of leaking, poor connection etc that will lead to poor battery performance. We need to fix any of these problems before further testing. If it can be fixed then battery is still serviceable otherwise needs to be replaced.
Pass/Fail	Passed

Step 2	Check Electrolytes level in each battery cell
Result	They are all at good level. Plates are all fully immerged s.
Explanation	If plates are not fully immerged, battery could not hold enough electricity. If electrolyte is level is low we need to refill the electrolyte before we do any further testing.
Pass/Fail	Passed

I removed the surface charge of this battery by disabled the ignition system and cranked engine about 15s. (Surface charge will give us a higher false reading than battery is actually holding). Then switch off the engine and carry out the following tests

Step 3	Open circuit voltage test (OCV)
Result	12.6 V (100% charged)
Explanation	This test show that this battery is fully charged, its state of charge is 100%. It is in good condition. Now we know this battery could hold 12.6V, we could now move on the load test. If state of charge of the battery is below 50% or 12.4V. Below 12.4V may indicate the battery is faulty or simply not fully charged. Need to be recharged and perform further testing.
Pass/Fail	Passed

Step 4	Hydrometer testing (advantage over OCV is we could determine the condition of each cell)
Result	Reading 1300 1300 1300 1300 1300 1300 Colour clear clear clear clear clear clear
Explanation	In realty, we can choose to use OCV or hydrometer testing. OCV seem to be more popular. Both of these test gives indication to battery’s state of charge. 1300 indicates that is battery is fully charge. The color of electrolyte may indicate a problem if it is not clear. There is no difference between cells. The maximum difference is allowed between cells is from 25 to 50. There is nothing wrong with this battery so far.
Pass/Fail	Passed

Step 5	Load test (205A load applied for 15s)
Result	This battery held stable 12.4V
Explanation	This battery is well above 9.6V mark. There is no problem with this battery. If it is below 9.4V is an indication of faulty battery.
Pass/Fail	Passed

In conclusion this battery is in a good condition and passed all tests.

l  Physically nothing wrong with it,

l  Electrolyte level is good in each cell

l  Able to hold a full charged voltage.

l  Capable to hold at least 12.4V under heavy load.

Battery testing

Battery testing

Battery testing is one of the most important tests. Before the condition of battery is determined, starter and alternator tests can’t be performed correctly.

I used the following general testing procedure is listed below to test a Lucas 127MF battery with CCA rating of 410A:

1.         Visual inspection

2.         Check electrolytes level

3.         Check the state of charge of this battery by OCV or hydrometer testing

4.         Load test to determine whether this battery could hold at least 9.6V when large load is applied for about 15s.

Testing Result

Step 1	Visual inspection
Result	No corrosions, Oxidation, Physical damage of any form, Deformation is found. Terminals and plugs are clean and tight. Only thing need to mention is that this battery needs to be mounted.
Explanation	There is no sign of leaking, poor connection etc that will lead to poor battery performance. We need to fix any of these problems before further testing. If it can be fixed then battery is still serviceable otherwise needs to be replaced.
Pass/Fail	Passed

Step 2	Check Electrolytes level in each battery cell
Result	They are all at good level. Plates are all fully immerged s.
Explanation	If plates are not fully immerged, battery could not hold enough electricity. If electrolyte is level is low we need to refill the electrolyte before we do any further testing.
Pass/Fail	Passed

I removed the surface charge of this battery by disabled the ignition system and cranked engine about 15s. (Surface charge will give us a higher false reading than battery is actually holding). Then switch off the engine and carry out the following tests

Step 3	Open circuit voltage test (OCV)
Result	12.6 V (100% charged)
Explanation	This test show that this battery is fully charged, its state of charge is 100%. It is in good condition. Now we know this battery could hold 12.6V, we could now move on the load test. If state of charge of the battery is below 50% or 12.4V. Below 12.4V may indicate the battery is faulty or simply not fully charged. Need to be recharged and perform further testing.
Pass/Fail	Passed

Step 4	Hydrometer testing (advantage over OCV is we could determine the condition of each cell)
Result	Reading 1300 1300 1300 1300 1300 1300 Colour clear clear clear clear clear clear
Explanation	In realty, we can choose to use OCV or hydrometer testing. OCV seem to be more popular. Both of these test gives indication to battery’s state of charge. 1300 indicates that is battery is fully charge. The color of electrolyte may indicate a problem if it is not clear. There is no difference between cells. The maximum difference is allowed between cells is from 25 to 50. There is nothing wrong with this battery so far.
Pass/Fail	Passed

Step 5	Load test (205A load applied for 15s)
Result	This battery held stable 12.4V
Explanation	This battery is well above 9.6V mark. There is no problem with this battery. If it is below 9.4V is an indication of faulty battery.
Pass/Fail	Passed

In conclusion this battery is in a good condition and passed all tests.

l  Physically nothing wrong with it,

l  Electrolyte level is good in each cell

l  Able to hold a full charged voltage.

l  Capable to hold at least 12.4V under heavy load.