Capacitor

  This type of device is used to store electrical charges and prevent voltage spikes. The insulated plates area provide a form of storage into which electricity can flow and this prevent any surge of voltage. The unit for this is Farad (F) capacitance. The key thing that makes the capacitor unique is that the storing of charges takes time, hence it can be uses to dampen voltage spikes, or for event timing.
I. RC time Delay or "charging time":
   1.Theory:
   What really happens here? This can only be explained using electron flow theory. So the plate connected to the Pos is the positive plate, and the negative plate connected to the negative of the battery. Eventually, positive charges are attracted to electrons and vice versa, and hence the effect is similar with the diode. But because between 2 plates is the insulator, positive and negative charge don't meet but still get attracted hence keep storing up on the plates storage, this is called charging. At first there is plenty of room of storing so the charging is really really fast, then it is getting tighter so the charging speed drop exponentially, until the capacitor reach it maximum capacity, there is no more storing.
   When the capacitor is disconnected from the battery, there is no force to keep the charges together, hence they are more attracted to the rest of the circuit( conductor), or yet trying to flow through an easiest way to get to each other( positive and negative), this is called discharging. Discharging can be dangerous, because if charging is exponential-like, so is discharging. The speed of discharging at initial is the biggest because the maximum number of charges bunching up wanting to get out! And that is the magnitude of the current flow. Remember physic 101! Current is essentially Coulomb/sec it means how much charge flowing through a second!!! So with a big capacitor releasing its energy, DON'T BOTHER TOUCHING IT!!!  
   2.Calculate how fast the capacitor should charge
               T=RxCx5
R: resistance Ohm ; C: capacitance Farad; T is time in second.

II. Build the circuit

This circuit has a resistor in series with a bridged capacitor, and a voltage source of 12V.
The resistor is, as always to control the current in the circuit. Excessive current can damage the capacitor, overheating the plate, damaging the insulator. The capacitor is there for our benefit of understanding how it works in a circuit and how it charges and discharges.
The capacitor once hooked up with a source will autoly charge up. Therefore we make a bridge across it so electricity will flow through the bridge, as the easiest way to get to battery negative, completing the circuit, plus most importantly it prevents the capacitor from charging.

Once the bridge is disconnected, the capacitor starts charging up. By correctly hooking up th Voltmeter, we can read the charging value as voltage drop across the C keeps increasing,as it is charging. So once we disconnect the bridge, we start recording the VD every 10 seconds for 180 seconds, hence draw a graph for voltage change over time. And what we've got is a logarithism-like graph. The very steep slope from the start indicating the fastest charging speed as the capacitor is initially empty. As the storage is getting fuller, the slope becomes more gradual over time, indicating that it is actually harder to get charges stored fast, hence the charging speed gradually decreases. The last few seconds, the slope is getting very close to zero, showing that the capacitor is full.

Testing Diodes

  While most of the calculations on electrical circuit are done with conventional current- means that current flow is from positive to negative, Electron flow is actually what happens that electrons go from negative to positive, because they are attracted to the positive charges. Bases on this principal, a semiconductor device called diode is constructed, which only allows current to go only one way forward biased. Apparently, positive charges of missing electrons and electrons are pushed oppositely from the positive and the negative, towards the middle boundary layer. The positive charges are missing electrons so they have "holes" available for flowing through, because the electrons don't stop there but keep being pushed by the negative. A current can flow through a "forward biased" diode because of this.
In a "reversed bias" situation, current can not flow when Positive is connected to the Cathode, that the positive is more likely to attract the electrons side of the diode rather than pushing them.
   When "testing diode" resistance becomes practical, there are 2 ways.
  When testing a diode using Ohms meter, make sure that the meter is "strong enough" to push the holes and the electrons through the "boundary layer", in order to be able to "turn on" the diode. Some small multimeter is incapable of this, we either use a stronger meter or, switch to "old" analog meter that is actually capable.
   Remember when we check the rectifier diodes out of the alternator, we did use the diode test setting on the multimeter. What the meter does is using a higher voltage to push the diode, then it will record the voltage drop required to do this, hence this VD is correspondent to the diode's resistance. By measuring the diode in both directions, from anode to cathode, the resistance should be low because it is possible to flow through the diode. The resistance from cathode to anode should be infinity indicating that the blocking is functional.
  During our assessment, we must build a simple diode circuit incorporating a 1k Ohm resistor in front in series. A small diode like an LED has very little resistance itself hence the current flowing through it would be huge, eventually will "kill" it. Therefore, a big resistance is added to control the current flowing in this series circuit. Later on, a LED replace the current diode. Because the LED is a light-emitting device, hence it needs higher resistance to draw enough voltage to shine. The rule of electricity is again in action to tell that in a series circuit, the component with the most resistance will require most of the Supply Voltage to push the flow through.

Relays!!!

 Through theory, I only know that "A relay uses a low amperage circuit to switch on a higher amperage circuit"(theory note). Now I understand what its for.
By the wiring diagram, from the battery, we have to spit into 2 parallel ways through the relay compound. It is divided into 2 parts: control circuit, at which we wire the battery with the 86, and out put is 85, then wire it to the switch creating a negative switch. The other one is the switch circuit, which consists of 1 input the 30 and 2 outputs 87 and 87a. Now this is where i realize that it is just the logic that my head keeps spinning.
The resistance from 86 to 85 is 75.1, from 30 to 87a is Infinity, so is from 30 to 87.  This is because without the negative switch closed, the relay can not pull the switch from 87a back to 87, so as the relay stays off, the switching circuit between 30 and 87a is NORMALLY closed. And there is a switching circuit that is NORMALLY open when the relay is off, it is 30 and 87. When i try to wire a similar diagram to the relay, i try to measure the Amperage through 86 and 85 while the relay is on, the result is 0.16A, a small amount. So any doubt about the theory is finally rectified that the switching circuit uses a small current to switch on the big current for the main consumer circuit.
To demonstrate our full understanding of the relay, we are to bulb a circuit showing a relay circuit controlling 3 light bulbs in parallel:

When

When the Neg switch is closed, 85 n 86 are completed, and a current of 0.16A is through them, which excites the mag-coil, creating mag-force to pull the switch from 87a to 87. That's the whole job of the relay. Now, with the 30-87 closed, the three bulbs will light, and a large current measured is 0.75A.
Because the 87a is normally closed when the relay is off, hence it can be used to switch between "high beam" and "low beam" similarly to real car application. So, hereby the AV @ 87a when the relay off is nearly equal to the supply voltage e.g 13.4V and 13.11V, while AV @ 87 is Zero, and vice versa.
A big Voltage Drop can also be found across 86 and 86 when the high resistance relay coil (approx~75Ohms) consume almost 13V of the supply AV. Evidence is the AV @ 85 is 13.39 when Off and 0.38 when ON.

By this wiring, we can switch between low beams and high beam by OFF and ON. On a further context, some headlamps are designed that low beams remain turned on when the high beam mode is turned on.

In the event off 87a is already on when the relay is off, a bridge is made so that supply goes straight to the low beam circuit, small bridge, just enough to provide sufficient current for the 2 small bulbs. When the 30 and 87a is connected, the bridge will be shorted. When the relay is on, High beams are on also small beams remain On.

Identifying, Testing Combining RESISTORS

When you see a resistor, you want to know what its value, so you must know how to read it. After the assessment, I've learned that there are 2 main parts that you need to know.
I. Know how to calculate
SI Units are important, K is for Kilo, its means x1000
                                 M is for Mega, means x100000
                                 Another m symbol, its called Micro means x10^-6
and etc etc...

II Know how to read color codes
Don't panic, its easy!!! There are normally 2 types: 4 color codes and 5 color codes
With 4 color codes: the First 2 are numbers to take down eg. Brown/Red so is 12. The 3rd one is how many "zeroes" to add in eg,Brown/Red/Blue so 12 x 1000000(6 zeroes to add in). Just compare with the color code and better yet remember it.
The last color band you often see @ the end of it is gold or Silver, these are tolerance value means that you add or minus 10% or 5% of the calculated value.
5color codes, "same wine, but bigger bottle" the 3rd can also be taken down as a number, the 4th is the "ten-to-the-power-of-corresponding color".

III Series and Parallel
  Why resistance adds up in series, because same principal with water, 2 sequential resistor will be like 2 narrow stoppages, hence it is harder to flow. Rt=R1+R2+R3+...Rn
  Why in parallel, Rt behave accordingly to the formula . Simple, just like water if you have a path leading away to 2 path, eventhough there are resistances on each but, add those 2 paths 2gether, you'll get double flow, the total resistance will be 2 small proportionally to the series ones.

End of the story.

Starter motor full mirror!!!! Part 3

On car testing:After the starter motor is torn in and out to check for faults; it is time to check the one on an engine. This practical test is indeed essential in real-life diagnosis and relevant to most regular cases.
What if it is not the battery that fails your car to start, after you have checked there is 12.7V OCV. Turn the car on and it doesn't sound like cranking, but you hear a little click. AHA!!! It is the plunger that still operates.
Those are just saying, but before blaming the starter, check all the wiring first. The circuitry between the battery and the starter terminals and body might contain potential voltage drops that could result in not enough power/torque produced to crank the flywheel. Hence we should put the voltmeter for a test. Parts that need testing are: Batt+ to B terminal(spec is below 0.2V, this is to ensure good condition of conductor); B terminal to M terminal(spec is below 0.1V); and starter body to Batt -(spec is 0.2V). Any higher VD reading shows that the battery will fail to deliver at least 9.5V for cold cranking. These parts are in series, therefore a total of all 3 reading must also be below 0.5V. AND, all the tests must be measured while cranking. Why, because this is the test where the starter is to put to crank the engine, so we only get its readings when it is cranking.
Next, the amperage delivered to the starter to excites the armature must be sufficient in order to produce enough cranking power. With old engine, the reading is expected to be a little bit less than the spec(e.g 110A out of minimum of 125A) this is because moving parts are smoothened(commutator brushes, shaft, overrunning clutch housing etc...) hence power required is a bit less.

Starter motor full mirror!!!! Part 2

  Now learning and understanding is such a "sweet" job. But the main purpose of that is what can we really do with the component. Therefore a dedicated dismantling and analyzing are required to fully fortify understanding of the topic. On May 6th we had our starter motor bench testing and repair assessment. So i'm gonna go through what we did to test it and why we did that.
   As I explained earlier, there are 2 main circuits in a pre-engaged starter motor, they are plunger circuit or the "control" circuit and the Armature circuit, which both consist of many components. But, there is only one input and output out of the whole thing, plus the two circuits are logically connected, therefore the first test we must do be4 dismantling is testing the winding using multimeter. On the body of the plunger circuit, we need to distinguish 3 terminals: one is for the Ignition Switch(S), one is Battery Input(B), and the other one is M-starter motor supply in.
    Winding(Coil) test consists of 2 sub-tests: Ground test and internal circuit test. With the ground test, set the meter on 2k Ohms, connect one lead to any end of the winding and the other to the body. This test is to find out if the winding is shorted to ground or not. If it is shorted, the reading should be a number amount of resistance, hence the winding is faulty. Short-circuit is the most common, most deadly enemy of electrical circuit. It makes the conductor contain an overloaded amount of current through it, hence this leads to overheating which fatally damage the circuit and any component within. Therefore, the correct reading for this test should be infinity, indicating there is no  circuit between the internal circuit and ground.
With the internal circuit test, the resistance reading should be low, just as the specification so that the resistance is controlling the amperage. A lower resistance reading results in higher amperage, hence the risk of overheating is higher. This could be caused by a short circuit inside the internal winding, causing the resistance to fall as electricity is taking a shorter path. And such a high resistance reading tells us that the circuit does not have enough current flow, hence the power output is insufficient for the whole operation. This caused by damaged or corroded conductors. Or significantly, an infinite reading tells us that there is a break in the circuit, which could be caused by those reason.
  
With great result from that "surface" test, now simply we need t know if this starter can work. So we put it on a bench tester to simulate its operation. The way we hook it up the tester is relevant to how we actually put it in our cars. So Battery to B terminal, Ground to Battery negative, the Ignition Supply to S terminal. It is actually easier to run the starter on a bench than trying to run it off-car, which is also COMMONLY POSSIBLE. Because with the bench when the switch is hooked up, we have our switch buttons for both battery to kick in and ignition to close the circuit. But with the off-car test, unless or even you have a switch simulator, battery is always "on" once you hooked it up, and without the switch simulator, you'll have to touch the switch cable to the S terminal, which is quite unpleasant and it is easy to short-circuit the whole thing.
OK the starter on the bench test is called a "no load" test. This is simply because it does not crank the flywheel, in which a higher power out put required is higher. When the switch is on, the voltage supply should drop, but not below 11V, hence the current provided must be also high enough between 30-50 Amps. When it is actually on a car, the voltage minimum required to crank is 9.5V, so 11V is a safety margin when testing with no load.
    
     Now, disassembly! This is a very practical part of the whole assessment, also very relevant in some real life situation, when you have to pull it out to see whats inside. Instruction is ok but nowhere to be needed because as you take the screws out, the coils and springs start to disassemble themselves, pushing almost everything apart. So what i learned from doing this is: try to do this slowly, remember where to put the bits( O-rings n stuffs) back, alignment is also important as when you put it back. It is actually more organized(which is the whole point of doing this) if you try to take one out of a time and test it. The only pain i got was a dirty/old starter is hard to distinguish and a real pain to put back due to alignment problems. 
 THIS IS WHERE ALL THE DEDICATED INDIVIDUAL TESTS BEGIN!!!
Visual inspection is always the first thing we do. it helps us to quickly determine the problem if it is obvious.
I Armature test:
 The commutator is an in-contact component, therefore we must check its circuitry. Commutator segments and armature shaft must be fully insulated, hence the reading is Infinity. There must be connections between commutator segments to ensure ducting, so a low resistance reading is expected between 0-1 Ohms, between every segments. Thats why this is called continuity test, by putting a lead to a segment, and the other lead moving around the commutator bar. Also, diameter and depth of the commutator bar and the mica undercut are important as they decide the correct contact condition with the brushes. Alternatively, a 48V test light can be used 2 check its continuity.
For checking internal short circuit, we use the "growler". This device is able to check for short circuit using the V seat and a metal strip holding above and along the shaft. When the short circuit segment is in place, it will ignite some sort of electromagnetic surge that is strong enough to move the metal strip and hence the short is detected.

II Field coils and Pole shoes
Field coils are like force-multiplier for producing magnetic torque. Therefore between each end of the field windings, conduction must be good, it means small resistance. Commonly, if field winding is insulated from the body, which in this case it is, the resistance test should be Infinity.

III Brush Holder Assembly:
Firstly, brushes should be long enough to ensure there are firm contacts with the commutators, as described above. Remember the key is the shape of the contact, and the minimum length. Measure the length of the brushes, if they are close to the minimum, should be replaced.
With the brush holder, the key thing is between the body and the brushes must be insulated, otherwise the power circuit for the armature is sabotaged. We can check this by using Ohms meter, n it should read "I".

IV Solenoid magnetic switch.
By using a 9V supply tester, we can check the operation of pull-in and Hold-in winding.

In Pull-in test, put the 9V supply between S and M terminal. This simulates when the switch is closes, the current flows through both pull-in and hold-in, but pull-in wins, therefore, the result of the plunger got pulled in fast is expected.
In hold-in test, 9V is connected between S terminal and the body. This simulates when the contacts are closed by the plunger, the pull-in winding is shorted, only the hold-in winding in operation, and 9V flows from the switch, through hold-in, to ground. Note that when carrying out this test, plunger must be pushed in, so when the lead is grounded, releasing the plunger won't coil it out.

Those are the key things that need to be remember during disassembling and testing. And the rest, testing pinion gear and Overrunning clutch, bushes...re-assembling, just follow the instruction, because they are mechanically easy to comprehend.

Starter motor full mirror!!!! Part 1

   Starter motor is one of the MOST important parts of an engine. How important it is can be described as the margin between a sleeping engine and a running engine. What is does: crank the engine using its own power. Where does this "power" come from: battery. How does this happen: First it's the human who switches the ignition key that connects the control circuit to the starter. The control circuit consists of a hold-in solenoid widing and a pull-in solenoid winding. What most of my collegues don't understand was why hold-in and pull-in were activated @the same time. It is because same voltage applied for each winding, the one with smaller resistance will have a higher power output(i.e V=IR; P=IV) and hence the pull-in wins, which pulls the plunger to close the contacts for the main/ higher current/armature circuit. Also, the plunger is mechanically connected to the  moveable shaft of the armature, which connected to the pinion gear/running clutch bunch. So when the plunger is pulled in, this pushes the pinion gear in contact with the flywheel. That the whole reason why this stater type is called "pre-engaged".

When the contacts close, the pull-in winding is nolonger needed therefore the circuitry was designed to short circuit the pull-in winding.

   After pre-engagement, it is...engagement! The contacts close, the BIG current for the armature circuit kicks in, excites the solenoids that act like magnets to turn the armature rotating. The armature then spins so quickly because of huge magnetic force can effectively turn a circle of linear conductors cutting through it. And when the armature shaft turns, it creates torque, transfers it to the flywheel that moves the crankshaft. And thats how the engine is cranked and started.

 

   Aftermath, when the engine starts, the idle speed and the gear ratio of the flywheel make it obsolate for the starter to spin with them, this can cause so many damages like overheating parts and circuit(deadly), corrosion to the moving parts etc... Therefore, the starter needs to back down. How can it back down? Apparently, the human knows that the engine has already started, hence releases the ignition switch, in which the starter motor control circuit is switched open again. No excited solenoid winding to pull/hold the plunger, but the plunger arm needs to be pushed back. Fortunately, it already has a spring that coils itself back. In the end, the pinion gear is pull back from the flywheel. There is a notable part called the running clutch which is also essential that it protects the armature circuit from excessive torque by the engine. Its clutch-roller and spring housing system are designed to allow the housing to spin freely from the shaft when it is sensed that the flywheel is spinning faster than the armature's original speed. The springs will retract that will allow the rollers to contact-free with the shaft, making it possible for the pinion to spin with the flywheel without spinning the shaft. This operation is also connected with the ignition switch. So when the key is turned, the springs lock the pinion with the shaft, when it releases, the springs free the rollers.( To be continued...)