How does an ALTERNATOR work ? How to TEST each COMPONENT with a multimeter and how to REPAIR it ?

The battery light stays on on my car.
The alternator is in rotation but the battery doesn't charge.
After checking that the issue doesn't come from the car, I test the alternator on the table.
I test it with a drill and observe that it doesn't work.
Before to open the alternator, I explain briefly the role of the
stator and the rotor.
I show you the schematics of the components of the alternator :
The stator, the rotor, the regulator and the diode bridge.
I test the rotor with a multimeter
I test the regulator, this doesn't work.
I test the stator and the diode bridge together and separatly.
I notice that a diode is in shortr circuit on the diode bridge.
I replace the diode bridge by a new and I refit it on the alternator.
Then I refit the alternator in the car.

0:00 Introduction
1:06 Test of the alternator in the car
5:41 Test of the alternator on the table
6:27 Alternator operation
9:02 Presentation of each component of the alternator
9:47 Tests just on the rotor
11:08 Tests just on the regulator
13:44 Tests on the stator and the diode bridge
15:36 Diode bridge removal
16:31 Tests just on the stator
17:52 Inductance measures on the rotor and the stator
19:05 Tests just on the diode bridge
23:02 New diode bridge refitting
25:56 Alternator reassembly and reffiting in the car

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This video has been created for practical, educational, and sharing purposes. It neither constitutes nor replaces a genuine specialized technical manual. EnjoyWheels provides no warranties of any kind and disclaims all liability for the information contained in the videos. Under no circumstances can the author be held accountable by viewers for any adverse effects resulting from the use of the information presented in the content. EnjoyWheels recommends wearing personal safety equipment when carrying out tasks similar to those shown in the videos on this channel. If you are uncertain about the potential dangers of an operation, its consequences, or your own ability to perform it, seek assistance from a professional.

[ciriloarellano]

As a retired mechanic this is the first time the battery harging system has been explained properly and simple to understand. Thank you.

[ibyquhr]

One of the best explained alternator repair videos ever ! It should be used in high schools. Thank you!

[Zac_LDN]

This is THE best car alternator/battery diagnostic video I’ve seen. 10/10!

[nalo]

this is the most detailed alternator repair ive watched. 27mins not wasted . you sir earned a subscriber

[bobbymathiwathanan]

What can I say? The best best super alternator repair video on YouTube. Thank you so much sir

[frankflowz]

Am paying a lot of money for my engineering degree and am watching this for free 😂😅

[pitchforkpeasant]

Have never seen a better description and demonstration at the same time. Ever. 👍👍👍

[jockofthebushveld]

Undoubtedly the Best diagnosis of non charging condition in a Vehicle, and Theoretical Explanation and repair and testing on a Alternator, I've seen well done.

[kjo]

God bless you, my Lecturer .That's my field. Also, I didn't know how to test the regulator ... but now I am thank you so much more blessings and may continue securing your life.

[chadmason]

You are the first to explain that the stator wires are in pairs. Even the shop manual wire diagrams don't show this but now it makes sense. I hate when they dumb down info because I know something is off and then understand that they don't want you to know that much. Just buy another and replace it!

[thefirstcalled]

Thank you very kindly for your demonstration. Finally, a guy who knows how to explain things in a straight forward and logical way. Bravo!!!

[JP-muic]

Thank you for unravelling another mystery of “how it works”. Very clear, full, and easy to understand production. Well done.🇬🇧

[spelunkerd]

This was fun to watch. Your work flow is very different than pro mechanics, yet still very engaging. Pro mechanics would simply swap the alternator, and a few with extra time on their hands would do a voltage drop test of the B+ wire and a ripple test to look for diode bridge problems. The ripple test could be as simple as switching your multimeter to AC to detect big swings in voltage as the device spins. In this case I like the way you pulled the three components apart and tested each in turn. At one time those three components were sold separately, but today it is hard to find individual parts that are all compatible. In the end it comes down to how much time you want to spend testing and then searching for parts.

[m.fuadfauzi]

Perfect work troubleshooting video. Complete step by step explanation and of course the theoretical. I will wait the next and more video from you. Thank you.

[davidleong]

Not only the step by step makes easy to understand, the diagram makes a great way for people to follow. Great job!

[WeekendMuse]

One if the not the best video on car alternators and troubleshooting I’ve come across on YouTube. Post-processing must have been time consuming but the end result is fantastic. A good mix between the practical and theory made your video highly engaging to watch. Also learned a few tips about soldering! Well done.

[jeffmccrea]

A good quick go, no go, first test:

1) Turn the key to on. DO NOT START THE ENGINE!
2) Take a screwdriver, plier or anything steel and touch it to the shaft in the middle of the alternator pully. If it sticks hard like to a strong magnet, the voltage regulator and the field coil wrapped around the shaft are probably good.
3) Go to the other tests shown here.

When you go to test the diodes with a multimeter, you MUST know the polarity of the test leads. Depending on the meter brand, the internal battery voltage supplying the probes are not necessarily the same as the probe color codes. Example: Radio Shack and Archer meters made in the 80's and 90's had the red probe outputting a negative voltage as tested with another volt meter.
A diode is a "semiconductor". This means when functioning properly, it will pass power in only one direction like a one way valve will only pass a liquid or gas in only one direction.
If your continuity or ohm meter has a negative going red probe and you connect it to the anode, (flat bottom end of the diode in the diagram), and the black probe to the cathode, (the pointed end), you will get an indication that the diode is open, (burned out), when it may be perfectly good.
When testing diodes in an alternator, they MUST FIRST be disconnected from the stator coils or you may read a shorted condition by inadvertently reading the continuity of a stator coil rather than the diode itself.
Whenever checking any semiconductor whether it be in an alternator, amplifier, radio or crystal set, first, set your meter on the X1 or lowest ohms setting then connect the positive going probe to the anode and the negative going probe to the cathode. It is normal to read a few ohms at this point as semiconductors are not a perfect wire. Now, reverse your probes and test again. There should be a 0.0 or infinity reading or, on meters with a needle instead of a digital readout, zero needle movement. If you get any reading at this point, the diode, (bridge in an alternator), needs to be replaced.
Another indicator of shorted diode(s) in an alternator is a lower than normal, but present, charging voltage at the battery with the engine running. Normal charging voltages vary by car brand. Ford is between 13.2 and 13.5 volts. General Motors, (GMC, Chevy, Buick. Oldsmobile, Cadillac, Pontiac and Saturn) is around 13.8 and Chrysler, (Chrysler, Dodge and Plymouth) is 14.2. Chrysler police vehicles can be from 14.5 to 14.8 because of extra equipment.
Older 12 volt vehicles with generators, at idle, readings can be below 12 volts and still be normal. Increase engine speed to 1, 000 RPM and test at battery for 12.8 volt or above reading not to exceed 13.8 volts max.
Foreign brands, check with dealer service department for acceptable voltage range.
Two ways to test for shorted diode(s).:
1) Set your radio to a dead channel in the AM band.
2) Start the engine.
3) Rev the engine slightly. If you hear a soft hum that changes tone like a siren that changes pitch with engine speed. This can also be noise from the ignition system. If this hum is present, with the engine running, take your meter, set it to "AC" at or near a 12 volt setting and place the probes on the battery terminals. (This will NOT harm the meter.) There should be NO reading at all. If the meter reads any voltage of any kind, one or more diodes are shorted supplying AC voltage to the vehicle's electrical system. This leads to a lower than normal effective charging voltage, could damage the internal filter capacitor in the alternator, irritating noise in some car radios and, if the ECM, (engine control module), has poor filtering or is "well aged", this alternating current, (AC), can confuse it leading to less than optimal engine performance, higher pollutant output and / or lower gas mileage.

[charlescamen]

your video format with the real life and then the graphic representation is excellent and helps understanding.
thank you.

[maryfowler]

We did the Volkswagen alternator is just like that. Good to see somebody else doing the same have a nice day may you be blessed by all the different things in life. You already work the magic lesson share what you learn and be humble

[crazypj]

That was a really good explanation for anyone learning electrical repairs on cars.
I'm surprised you actually mentioned the diode direction of 'flow', that's very rare outside of an automotive school environment.
Well done.