How to Test an Alternator ( Testing the Voltage Regulator, Diode rectifier and Stator)

[Music] hey guys how's it going today I'm gonna show you how to test an ordinary in your car this is the part two of my video on how to tell if a car has a bad battery or a bad alternator in part one you're looking at four ways to diagnose a car battery today you're looking at the alternator and I'll show you guys some common alternatives which you can easily diagnose by yourself so if you're a beginner and you're watching this to diagnostic has alternated this will be a complete guide for you now that's enough talking let's begin every time you turn the key to start your car you will see your barrier light comes on which tells you that your battery is not getting any charge after you start the car the light should go off as the alternate is providing electricity to maintain the barrier and the electrical demand you can either on if the light didn't go off after you start the car or the light comes on while you're driving that indicates you have an alternate a related issue let's start with basic alternator voltage test using a multimeter first even I connect the multimeter to the battery and even check the Barry voltage then even start the car and say the alternate charging voltage as you can see I have around thirteen point nine volts and that indicates a good charging voltage charging voltage in a car depends on four main factors Ryan temperature of the alternator state of charge of the battery Lord on the alternator and the barrier temperature in general the range between thirteen point five volts and fifteen volts is considered as a good charging voltage but modern cars have ECU control alternators that has a much wider range so you wanna check the service manual for Yoka to find out that set voltage range for your car's alternative before you start testing you can find these service manuals online or you can buy a book like this they are real handy and they have all the information you need didn't I do a load test on the alternator you turn on the headlights AC and as many accessories as you can this will increase the electrical demand on the alternator alternators have higher efficiency at higher rpms so even erase the engine rpm to around 2000 in this cap the rated alternator voltage range is between thirteen point two volts and fourteen point eight volts as you can say I'm getting around thirteen point five volts which is well within the specs just like the battery alternators also have positive and negative terminals positive terminal is called v post it is connected to the battery using a cable and the cable goes inside the wiring harness to the fuse box and unto the battery a negative terminal is alternate housing here's the negative wire going out from the battery and it is bolted on to the cars chassis so the entire cast chassis becomes a giant negative terminal so different components in the car can share the body as a ground connection here and wire goes to the engine because the alternator is bolted on to the engine the alternate housing becomes a ground for the alternator then you wanna connect the multimeter directly to the alternator now we have to compare this reading against the previous reading we had on the battery if you see more than 0.5 volts of a difference in the readings heha voltage drop between the battery and the alternator so even find where the drop is let's check the positive side first connect directly to the B post and the black plate to the positive battery post the rating should be less than 0.2 volts and I only have a few millivolts if the rating is about 0.2 volts you know check between the B post and the cable and also between the cable and the very post if those connections are good then the cable itself is bad and you have replace it to test the ground connection connect the red lead to the alternate housing and the black lead to the negative post on the battery again the reading should be less than 0.2 volts if it is more than 0.2 volts you have bad ground somewhere so you wanna check all the ground connections until you find the bad one you also wanna check the alternate amount because that is where the alternate is getting the ground if you found any bad positive O'Brien connections you wanna take more give it a good clean apply some silicon paste and reinstall them back that's how we do basic ordinary test using a multimeter diagnosing alternate ratios in a car requires some serious testing than this let's start with robots alternators are driven by tribals so if you hear a squealing noise when the engine is running and the alternate is under charging the first thing you check is the drive belt to see if it is worn out or to lose if you notice little cracks or shiny strips on the belt that indicates a worn out built and you know replace the belt if the belt is too loose you may have a bad build tensioner so he had replaced that some modern alternators comes with decoupler pulleys which act as a clutch to eliminate built vibrations so that the engine can run very smooth but they can fail over the time and may create an under charging condition a failing decoupler pulley will make a rattling noise right after you stop the engine and eventually it will rattle all the time to replace the decoupler pulley you're not going to pick like this to take off the dust cap now that's what I'm talking about that is all the clutch material from the worn-out clutch then you need a 17 millimeter hex socket and an impact wrench based on the pulley if you don't have an impact wrench you can also use a breaker bar with some wd-40 now it is time to take a look inside the alternator first you know remove these three bolts to take off the dust shield then you know you know these four bolts so you can take off the front housing if your alternator is friendly and if it is not the decoupler pulley then it's the bearings that making the noise and look how easy it is to replace them alternators use electromagnetic induction to generate electricity so the alternate also needs some electricity from the battery so if you're having a noise or an intermittent charging issue the first thing you check is the power connection to the alternator you can easily do this with multimeter so I connect the black plate to the negative battery terminal and knees directly you can take each terminal inside the connector the top tip here is to get a small pin to probe into the connector so even damage the terminals you can also use a desk light or a Power Pro for this and he can use a wiring diagram in your service manual to identify the wires if you are getting a bad rating at the connector then you have to check all the wiring for any shorts or damaged wires you also want to check the fuses and relays for the alternator a good fit should look like this modern cars are very sensitive to voltage variances so you know check old fuses for assistance and make sure that they are all within specs to test realize you can eat some jump wise to manually operate the relay or you can get a relay test like this they are real East work wit and also very inexpensive in some cars the power of the ground supply to the alternator is controlled by the ECU in this type of a design you can use jumper wire to bypass the issue and manual supply power or ground to the alternator if the alternator is then working then either the wiring coming from the ECU is bad or the issue itself is bad if that is the case with you you have three options bypasses you rebuild ECU or replace this you before we going further we have to learn how alternators work when the alternate is getting current from the battery this current goes straight into the voltage regulator depending on the battery voltage the voltage regulator then adjusts the amount of current it passes on to the brush assembly the brush assembly is contact in these two slick prints so this rotor is now getting current rotor has a lot of copper winding so in the rod is getting current it becomes an electromagnet around the road is a stator and it's also made of three separate copper windings each end of the winding is connected to a couple of diodes so when the rotor is spinning it induces a current on the stator because the rotor is continuously spinning the polarity of the magnetic received by the state is also continuously changing so as the direction of the current being generated on the stator this is called the alternative current because attorney needs direct current this current is then sent through a couple of diodes to convert into the direct current because this data has three separate windings and each one needs two diodes for the can you Asian six tires are needed in total this six pack of diodes is called the rectifier the other end of the rectifier is the B post so this DC converted current is going to the battery now we have test each of these components to test the voltage regulator even up you engine to around 2,000 rpm and you know take a reading on the multimeter then you erase European few times and see the voltage again you shouldn't see a rise in the voltage between higher rpm ranges as you can see I get a steady rating of thirteen point nine at all times if the voltage is rising as you rev the engine that means voltage regulator is bad this is the main reason for an overcharging condition in most alternators voltage regulator is very easy to replace modern cars have easy control alternators where the power supply to the alternator is regulated by the class computer if the wire that carries current can be turned on and off multiple times in a very short period of time the average voltage on the wire can be changed the percentage of the time the Y is turned on in a given time scale is called the duty cycle so in easy control alternators EC is sending a duty cycle signal to the voltage regulator which means the current on the wire goes to the alternator is turned on and off hundreds of times a second by controlling the duty cycle ez can control the average voltage on the wire when the voltage regulator receive this policy in signal the alternator can then generate just the right amount of electricity the EZ needs voltage regulator also sends a signal back to the ECU so that the ECU knows how much current is generated at the alternator basically what you do is to identify the two wires that comes from and goes to the ECU and check the duty cycle on both wires if the EC is not sending a duty cycle then the wiring between the ECU and the alternator is bad or the ECU itself is spared you need to know that ec is also receiving data from other sensors to decide the duty cycle that goes to the alternator so to test this entire system you need to have an IV d2 scanner that can rave live data on the other hand if the voltage regulator is not sending a signal back to the ECU then the voltage regulator is bad unfortunately you cannot test a duty cycle signal using a multimeter and you need to have an automotive scope for that and they are very expensive let's have you test a voltage regulator in an easier control alternator the next thing unit check is to brush assembly because the brushes are spring-loaded they are always pushing against the slip rings if they are worn out and too short they will not make any contact with slip rings which might cause an intermittent charging issue in the beginning and lead to a no charge condition eventually so even make sure the brush length and make sure they're making good contact with the slip rings if the brushes are worn out you can easily replace them the top tip here is to use a pin to lock the brushes in place so you can easily place them around the rotor to check the rotor you can do a simple continuity test and also the resistance across the slip rings should be around 2.7 ohms testing the stator is similar to test in the rotor you just have to check the continuity now we have come to the rectifier rectifier acts as a one-way rail for the current so turn the dial into diode test mark and connect one lead to the B post and the other lead onto the alternator housing then even swap the leads over and see the reading again if the rectifier is good you should have very high rating in one direction and zero rating in the other direction if you are in this test while the alternator is in the car then take off all the connections before you begin another way to check the rectifier is to check the alternating current output on the alternator even though the alternator is supplying direct current a very small man of alternative current is still coming through the rectifier so now you are turn the dial into AC volts and see the rating for many older cars the reading should be less than 50 millivolts but some modern cars are rated up 200 millivolts this is a very important test to do in an alternator an alternator can have a very good charging voltage but it may protect too much AC current into the castle ectric L system which can trip trouble codes in other computer control systems which are designed to run by DC current also an internal issue alert rectifier is a very common reason to have an overnight battery drain as it is one of the very few components in the car that is directly attached to the battery the next question you may have is where to find the replacement parts for your alternator you can find these parts from spare parts ops or from wine shops some ordinary parts are very easy to replace while some needs special tools to work on them so if your option is to replace the alternator you have three choices buying a brand new alternator finding a used one or buy a remanufactured ultra here some high-end cars use vertical alternators and finding a used one could be challenging so buying a brand new one is the only way to go I already have another video showing how to replace an alternator I'll put the link to that video in the description down below now that's how you probably test and hold my Rainier car thanks for checking out this video and if you learn more do it yourself videos like this we can consider subscribing to the junky DIY guy channel so you will never miss another video all the tools I have used from this video are in the description down below so you can easily find them and I'll see you in the next one [Music]

Channel: Junky DIY guy

Views: 2,806,289

Rating: 4.7886972 out of 5

Keywords: Bad Battery or Bad Alternator, How to Tell If an Alternator is Bad, How to Test An Alternator Using Multimeter, Battery Light, Undercharging, Overcharging, No Charge, How alternators work

Id: 1bK0De9XOP0

Length: 14min 14sec (854 seconds)

Published: Sun Jun 11 2017