Minor correction, the voltmeter, set in continuity setting, measures continuity in ohms resistance. A diode is a one way resistor to AC current. If you get the leads wrong as you pointed out, a diode has infinite resistance. In the correct orientation a diode will have something in the neighborhood of 450-500 ohms of resistance, a shorted diode will have very little resistance and an open diode will of course show very high resistance or infinite resistance. The important thing, and I thank you, is teaching me how to test my alternator easily. Good video, good instruction giving.
Thank you very much for this. I have a parasitic drain after the car is switched off, which drains the battery in 15mins, the volts drop from 12.6 to 7 volts . Then I disconnect the negative terminal & the volts return to about 11.5. I will follow your instruction to test the diodes. Best tutorial ever, thank you again.
My 2001 Toyota camry is at 11 volts. I changed my alternator with a new alternator and it's still at 11 volts with a load? In this particular alternator the voltage regulator is included in the Alternator. Kinda frustrating I cant figure out what wrong with it. Battery is good. Just for some reason its at 11 volts with a load. Any ideas sir? God bless 🙌 and may the one and only lord bless you.
If your alternator produces 11v, depending on milage of alternator - check brushes, voltage regulator, get a complete alternator, better go to mechanic or bring your alternator to AutoZone or similar store so that they could test your alternator. You need diagnostics, go to professional.
@@chrisr.986 sometimes if they say it's ok - it will be ok. Depending on milage you may need a new one. When it's getting hot may act different. Buying cheapest - not an option. I saw 3 cheap starters installed one after another one. I connected my oscilloscope to car to see what's going on. Mine was dropping to 8V in some moments. Midas changed it to cheapest, changed me premium, in a week alternator started to act similar to original damaged one. After complaining they installed new original. Fixed. My friend had a bad tensioner and belt, his got temporary fixed. Now he has some minor problems with alternator, he changed his voltage regulator - fixed completely.
ckecking my alternator with multimeter, ( negative probe on pos battery terminal, negative probe on alternator case) reads 440 millivolts. When the alternator/battery is checked at an auto parts place, their meter says charging at 14.4v but has a shorted diode. Is the miltimeter test limited as to what it can detect?
I found this video and searched the comments because of a similar situation. When I do this test I am measuring 515 milivolts, however the auto parts store told me "your alternator diodes are bad." Im wondering if there is some other way to confirm if the diodes are bad after passing this test?
@@EvanChartier-p7d .....its possible the auto parts meter reads bad diode based on a current industry standard. Some older cars, some say, have a higher threshold of acceptable readings on AC voltage leakage for instance than on newer cars. The same may apply to the diode test. The auto parts store should program in your car make and year for accurate test results .
First test does not isolate the alternator. A bad reading could be from anything in the car including the hood light being in the on position. Also this will not indicate an open diode only a shorted one. Shorted alternators are easily found with a standard amp draw test. Just disconnect the alternator and see if the draw goes away.
Its NOT the forward voltage you are looking for, its the reverse, which you should read zero. since there are 6 diodes in a alternator, you need higher voltage to test the back current. Also remember diodes react differently at higher temperatures, when back current breaks down. Best way is a scope when running, under a load.
Good afternoon my friend, My battery is in the back of the car with the negative cable disconnected. When I touch the negative probe to the alternator positive cable and bolt and the red probe to the alternator casing, the multimeter stays at 1. When I reverse the polarity with the probes, the multimeter still stays at one. This whole test wile the plug and cable are still connected to the alternator. Thanks in advance!!
The last test shouldn't have show a reading, which means the Diodes are allowing current to flow both ways & not one way as they should. So the last test means the Alternator is malfunctioning.
Minor correction, the voltmeter, set in continuity setting, measures continuity in ohms resistance. A diode is a one way resistor to AC current. If you get the leads wrong as you pointed out, a diode has infinite resistance. In the correct orientation a diode will have something in the neighborhood of 450-500 ohms of resistance, a shorted diode will have very little resistance and an open diode will of course show very high resistance or infinite resistance. The important thing, and I thank you, is teaching me how to test my alternator easily. Good video, good instruction giving.
While doing your test, my reading was 174 could this be causing tha drain to th battery? Thank You, Jon R.
Most likely you have a shorted diode which may be over charging the battery and killing it
Thank you very much for this. I have a parasitic drain after the car is switched off, which drains the battery in 15mins, the volts drop from 12.6 to 7 volts . Then I disconnect the negative terminal & the volts return to about 11.5. I will follow your instruction to test the diodes. Best tutorial ever, thank you again.
Your videos are very informative and short. Only necessary stuff! 👍👍👍👍👍
Very useful info
Just when I was gettin' used to Red on Red and Black on Black ! ;-)
👍😂
Luv your videos Godspeed.
Nice informative video.
Did you even check where you plugged the leads into your multimeter?
I dont understand why the black probe is plugged into the left portal of the multimeter. Is that correct?
@@TheHomy70 because is black input
Mr. Paul, can you show us how to identify and replace the bad diodes? We live in a throw away society and this could help. Thx
Correct
My 2001 Toyota camry is at 11 volts. I changed my alternator with a new alternator and it's still at 11 volts with a load? In this particular alternator the voltage regulator is included in the Alternator. Kinda frustrating I cant figure out what wrong with it. Battery is good. Just for some reason its at 11 volts with a load. Any ideas sir? God bless 🙌 and may the one and only lord bless you.
If your alternator produces 11v, depending on milage of alternator - check brushes, voltage regulator, get a complete alternator, better go to mechanic or bring your alternator to AutoZone or similar store so that they could test your alternator. You need diagnostics, go to professional.
@pfoxhound I did take alternator to autoparts store they tested it and said it was fine? That's what's weird?
@@chrisr.986 sometimes if they say it's ok - it will be ok. Depending on milage you may need a new one. When it's getting hot may act different. Buying cheapest - not an option. I saw 3 cheap starters installed one after another one. I connected my oscilloscope to car to see what's going on. Mine was dropping to 8V in some moments. Midas changed it to cheapest, changed me premium, in a week alternator started to act similar to original damaged one. After complaining they installed new original. Fixed.
My friend had a bad tensioner and belt, his got temporary fixed. Now he has some minor problems with alternator, he changed his voltage regulator - fixed completely.
@@pfoxhound TYVM sir
ckecking my alternator with multimeter, ( negative probe on pos battery terminal, negative probe on alternator case) reads 440 millivolts. When the alternator/battery is checked at an auto parts place, their meter says charging at 14.4v but has a shorted diode. Is the miltimeter test limited as to what it can detect?
I found this video and searched the comments because of a similar situation. When I do this test I am measuring 515 milivolts, however the auto parts store told me "your alternator diodes are bad." Im wondering if there is some other way to confirm if the diodes are bad after passing this test?
@@EvanChartier-p7d .....its possible the auto parts meter reads bad diode based on a current industry standard. Some older cars, some say, have a higher threshold of acceptable readings on AC voltage leakage for instance than on newer cars. The same may apply to the diode test. The auto parts store should program in your car make and year for accurate test results .
Great video, just what I was looking for...!✌
Hi Paul, What car brand did you work with more? We want to send a good scan tool to you.
Very informative video, thank you very much.
You are the best
Good luck
Nice!
First test does not isolate the alternator. A bad reading could be from anything in the car including the hood light being in the on position. Also this will not indicate an open diode only a shorted one. Shorted alternators are easily found with a standard amp draw test. Just disconnect the alternator and see if the draw goes away.
Its NOT the forward voltage you are looking for, its the reverse, which you should read zero. since there are
6 diodes in a alternator, you need higher voltage to test the back current. Also remember diodes react differently
at higher temperatures, when back current breaks down. Best way is a scope when running, under a load.
Good afternoon my friend,
My battery is in the back of the car with the negative cable disconnected. When I touch the negative probe to the alternator positive cable and bolt and the red probe to the alternator casing, the multimeter stays at 1. When I reverse the polarity with the probes, the multimeter still stays at one. This whole test wile the plug and cable are still connected to the alternator. Thanks in advance!!
So I just did the first one to my 2001 Honda Accord and it read .316 so thats a bad one right ?
What will it read if it is bad?
Exactly
Very high like 850 plus.....he said this
Engine running for this test?
Well, now we know what a 'good' diode-pack reading looks like. But what does a 'bad' diode-pack reading look like?
Meter set ti continuity to test diodes for resistance but why are readings in mV pliz
Actually AC voltage to DC voltage
Mine reads 998 so I guess it's bad and it ruined the battery also. 😡 These batteries are robbery now around $200.
I can't get a consistent reading...One minute it says 400-600, sometimes it says negative 900 🤷♂️
Diode failure = parasitic draw, interesting.
Most people usually replace the alternator me cause azzhole manufacturers and alternator shops wont sell them too you.
The last test shouldn't have show a reading, which means the Diodes are allowing current to flow both ways & not one way as they should. So the last test means the Alternator is malfunctioning.
That's what I thought.