How to Properly Test an Alternator (The Extra Steps the Parts Store Can’t Do)
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- เผยแพร่เมื่อ 9 พ.ย. 2023
- Have you ever had someone come in to the shop and say that their alternator is bad and there reasoning is because a parts store tested it and it failed. I’m sure you’ve had this happen or even been the one having it tested. Well many times the tests are not accurate on these machines. So what do you do?
In this video the Professor will walk you through step by step how to properly test an alternator and be sure 100% that it’s failed, failing, or passing. You’ll see how to prove an alternator has failed even though it’s passing all the parts store testers.
We hope you enjoy this and as always if you have any questions or comments leave them below! Thanks for the support! Enjoy.
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This is the classical old school testing I was taught. I find it surprising how often working pros today on TH-cam don't bother. As soon as they see lack of charging they stop and order parts. New cars are much more difficult to do testing on. The alternator is often hard to reach, and the signals between PCM and alternator are much more complex. Even so, I think drop testing of the power and ground side are worth doing.
Great video as usual. Just remember a lot of us aren't in a shop. We are DIYers. That's why we watch these channels. Many of us don't own a lab scope. Many of us own a voltmeter. Try at all cost to teach us with basic tools if at all possible .Lots of time we condemn a alternator if the output voltage is low still at the terminal on alternator. We can't check to see it the PCM is controlling the input. I personally love the videos. Great story about the broken motor mount. Would of never thought about that. Also, thanks for your honesty about when cars come back to bite you. That's what makes your channel so good. Andy
It's not impossible to check for pcm control with a meter if you know how the meter works and what you should expect to see. If you don't know then you should take it to a professional like this guy is. Or load your parts cannon..your call.
You can check for reference and or ohm out sensors or the cable itself from PCM to connector to verify the connection on continuity. You can check the pin at the PCM, voltage drop, all can be done with a DVOM to give you the average readings, but a oscilloscope is king, even if you buy the budget Uscope, sub $225 w shipping, you too can perform simple tests. It’s not too difficult
You need a scope to properly diagnose vehicles nowadays unless you are someone sort of super human that can record voltage every 20 milliseconds and graph it in your head.
Thank you for taking the time. I am a master tech in TN and i like to watch this kind of stuff to stay on top of it so I dont get to over confident.
Great video,Im a 30 year heavy and auto mechanic still learned alot! Keep up this type of video, you can never know to much !
New subscriber, and all great points people overlook. Especially about testing diodes, which people almost always, even experienced mechanics, overlook. Depending on the multimeter you can switch to AC volts, and some have a dual display, which will show both DC volts and the AC voltage on it, so that you can diagnose a failed diode pack without a scope. Others when in AC volts disregard the DC, so you get the AC voltage only. As well remember that there are 9 diodes in the alternator, 6 high current ones that feed the output, and 3 lower current ones that provide the excitation to the rotor, and those 3 also can have a diode fail. Most voltage regulators will have a terminal, or a place you can put a probe, to measure that field voltage as well, so your scope can test those diodes as well.
Top quality channel. A great source of information. Hopefully people can learn and share from this for years and years to come.
Stay gold.
Valuable procedures that really enhance accurate diagnosis ! Have seen quite a few no charge conditions corrected with a new alternator recur, due to bad grounds at the mounting bracket. Changing the part restored operation, for a while.... Read somewhere that half the warranty returned alternators actually are not defective. Sounds plausible? Voltage drop is king!---------Al.
Better than a textbook ! You have a lot of knowledge ! Thanks for sharing this very clear lesson !!
Very good point about loading the circuit you’re checking for voltage drop it takes BOTH current and resistance to create a vd One question about A/C ripple why wasn’t the generator tested loaded and unloaded? Does the 0.5vac ripple still not exceed 0.5 loaded? CHEERS
Superb teaching skills!
Great video.Thanks for sharing your experience..
Great Video. Always something new to learn.
Thank you for a detailed video
Thanks. This channel is a gem. You are a master teacher!
Just to be clear, the same thing applies to testing the starter that applies to the alternator. When you are testing power and ground to starter, you need to have someone trying to crank the engine so that there is a load on the circuit. You can have a power or ground test absolutely fine with no load, and go completely open when loaded. This applies to any electrical circuit, always test for voltage drop with the circuit loaded.
This is the kind if gentleman that will throw you out his shop if you approach him with "I read this is the problem on forums" Pay this gentlemans Diagnosis fee, let him repair it and move on with your life
Grade info thank you.
I must say from all the mechanics I watch on youtube, you explain t8he things at best. Keep up the good work
Awesome video sir!!!
Great video RAS
Great video
Love the ATS vids...
"LET'S SEE A TOOL BOX TOUR" LOVE YOU GUYS. YOU'VE CHANGED HOW I DO THINGS.
We will add that to the list! Professor is waiting for an add on to it which is why he hasn’t done it yet. He wants to do it with that on there. Lol
Always worth checking voltage drop from battery post to battery terminal
Great video with a lot of valuable and practical info. Do you also put a clamp-on ammeter around the B+ cable while loading the system with hi-beams, A/C, radio etc. to see alternator amp output or is it not necessary? Or is that done by the big Snap On battery tester?
That's 90 mV. not 900 mV..🙂. Thanks for sharing.
Yes you’re correct. Misspoke there. Sorry about that!
@@theroyaltyautoservice no problem. Keep posting new videos. Have a great weekend. 👍
My 18' Hyundai Elantra will idle with loads on at 12.8 volts all day long, it does not start charging the battery until cruise deceleration. This is why ( along with other strategies) this 2.0 NA Port fuel injection engine got me 48 MPG commuting back n forth to work everyday. If you didnt RTFM and went by old school rule of thumb of 13.5-14.5v youd probably think the alternator was bad.
Hondas and Acuras also output about 12.8V or so when the system detects that the battery is full or the battery temperature is too low (or high, I forget which).
I checked my wifes 22 passport and at hot idle loads on it was outputting 14.6. I was expecting what you mentioned. however for her system I didnt take the time to read up on it. @@abdul-kabiralegbe5660
@@abdul-kabiralegbe5660 12V8 with high engine compartment temperature is correct with a fully charged lead acid battery, as the terminal voltage, which with a fully charged battery is 13V8 at 25C, is going to drop as the temperature rises. Older alternators that charged at a fixed voltage, 14V4, or 13V8, irrespective of temperature, thus would overcharge the battery, causing it to lose electrolyte due to it being split into hydrogen and oxygen. Some sealed batteries, and some more expensive refillable ones, have a palladium catalyst in the vents to recombine this to water, slowing down the loss, but you always had to add pure water to the battery to give it a long life. Thus checking the battery water, and filling up at each service. Sealed batteries are the exact same now, just there is often a cover over the screw off caps, and they say sealed for life, as they know there is enough water there to get you out of warranty before a cell boils dry, and you buy a new battery.
Pull off the label, see the caps, and check the water, and you get many years more service out of them, and check the water monthly as well, even if it means you have to remove the hold down and the terminals to get to the caps. Done that to all mine, and got to see that they would last 5 years just filling up every 6 months or so, all cells taking around 100ml of water to fill up again. Otherwise would have had the battery fail around 25 months after buying, just outside the 24 month warranty. OEM battery had caps, but was never checked, despite it being part of the OEM service routine.
Thank you sr🫡
Thank you
Most of DIYs don't have access to such sophisticated test equipment(s).
But a multimeter is cheap, or even free at Horror Fraught, and well worth keeping in the vehicle, the free Harbour Freight one is good enough to use here, and accurate enough. Blow it up, get another.
One other charge problem to check is the drive belt for the aultonator is it tight enough .good video though
Great diagnostics ,I'm learning how to use a scope,could you tell me please what is a good affordable scope? Thanks
when is AC part 2 is coming?
Is .5 volts a standard for most circuits? Thank you . I wish I worked for you when I was young a work comercial😅. I'm a retired DIY now. Enjoy all your vids
What do you do with a 2015 Buick enclave where the converter is in the of the starter I’m sure there are other ones also
A simple Fluke meter can do what you need if you know how to use it.
If your concerned about the A/C ripple you can add a capacitor to your alternators output to help smooth it out assuming all the diodes are good the alternator is a three phase A/C generator so the ripple shouldn't be too excessive even without the capacitor but adding one in would help with that the battery doesn't care one iota about the A/C ripple though it could effect modules if they don't have their own power supply filtration built in
The decoupler on an alternator can cause you headaches. The customer comes in and says the charge light on the dash comes on at times. You do all of the above tests and everything checks out fine. Then you finally discover the Alternator Decoupler is at times slipping and thus triggering the computer that there is a fault.
Keep 'em coming my friend. Any day is a good day if I can learn something. Also if I'm not mistaken, and I am often, the reason you see the upper side of the AC ripple at all is because the rectifier circuit is a half wave rectifier. Seems like manufacturers would clean up that half wave ripple with a full wave rectifier and have a "pure" DC signal from the alternator. Just my uneducated opinion.....
from my knowledge it has a full wave rectifier but it has to have filtering after that to get that pure straight waveform and the battery is acting like a filter as well
No, that is a full wave 3 phase rectifier, as diodes are a lot cheaper than copper, so putting in 6 diodes, and only half the number of turns of thick copper (or for the cheap alternators the thicker CCA wire) to get the rated current output, is a lot cheaper than having to put in double the number of wire. Then make a larger case to fit them, and having to get much more expensive diodes, rated at 200V, as opposed to the regular diodes that are rated at 30V, and are designed to break over at around 40V, to handle the case of a load dump transient (which is part of the job of the alternator now, as electronics in a vehicle is so much more than when a generator was around to drive only a few lights and a coil with points), or a regulator failing and causing the alternator to go to full output. Ripple you see there 6 peaks per revolution of the alternator field past the pole pieces, because of the 2 phases, and at any time 2 diodes are conducting at the peak.
The larger lower ripple is because of the rotor turning once in the housing, and also the slower response of the voltage regulator modulating the average output voltage, as it is being aimed at a particular set voltage by the internal regulator module. Typically 14V4 when cold, and dropping to 13V8 as the regulator heats up, to closely track the actual battery temperature, but still provide a high initial current to charge the battery from cold, tapering off with time. With modern alternators getting controlled from the ECU the initial voltage set is zero for a few second,s to allow the ECU to gain control of idle RPM correctly, and start the cold start warm up and keep emissions down, then it is ramped up to get voltage to 14V4 for a few minutes, to provide a full charge to the battery. Maintained till the ECU sees the battery current start to taper off, as the battery approached full charge, sensed by the sensor on the ground lead. Then it will depending on the model, either switch to a 15V charge for a few minutes, to desuplhate the battery, set by a counter programmed per the OEM battery manufacturer as to best profile for this, or will drop the battery voltage to a set voltage as determined by ambient inlet air temperature, and engine compartment temperature (coolant return temperature) so as to not overcharge the battery, and all the time monitoring, so that the sensed ground current in the battery is close to zero, so the alternator provides all the engine and vehicle current draw.
this means that your alternator warning light comes on when the ECU detects the battery is being forced to provide current for more than 5 seconds, either due to the engine not running, or that the load exceeds the output 5 seconds after it has been commanded past 95% duty cycle on, and the alternator is not supplying this current.
As an addendum to my first reply, I actually love it when someone has a lot more knowledge than me and is willing to share it. Thank you for the replies.
I am old (77) shade tree guy and love these. Don't have a scan tool, but thinking about getting a LUNCHX431 CRP919BT would like to know what you think about it. I am on ss so money is one reason for this one.
Grasias
Awesome
thanks for sharing doesn't the computer control the fielding wish you would go thru that. also would be nice to see how E-Scan compares to like snapon scanner for diag codes on cars
Generally speaking, you could just check service data for theory of operation. Most of your newer vehicles are going to use computer controlled alternators, and more often than not, they use a PWM type of control system. And a lot of your newish vehicles will also use a Battery Monitor sensor, which is just a glorified amp clamp. They tend to just monitor the current being used or put back into the battery and under load, the computer will use a higher pulse width signal for a higher load, and lower pulse width for less load. You only need a cheapo scope for most alternator tests. You could use a $150 dollar Hantek scope or a handheld Owon for example. I have the Owon HDS200 series, the HDS270 I think, it's not beside me at the moment. I love that thing, it's a handheld 2 channel scopemeter. It has both a digital meter so you can check resistance and typical meter stuff, and a 2 channal scope. It's actually good enough to check CAN bus signals, I use that thing all the time.
would you trust a SCAN TOOL WITH A BT506 AUTEL HOOKUP ? I HAVE BEEN CHECKING WITH THAT SETUP AND GET
ALTERNATOR INFO WITH BATTERY VOLTAGE. but i dont know how accurate it is. i see your way is spot on.
First and foremost, thanks for the great video. I noticed a little issue: 0.09 volts is 90 millivolts(not 900 millivolts)
I was thinking the same thing too especially after he said he didn't want to see anything over 1/2 a volt which is 500 milivolts and 900 milivolts is almost a volt.
@@Mr2004MCSS I think it was just a slip up - he hasn't made videos in a while😅
Yes it was a slip up. Sorry about that.
@@theroyaltyautoservice great, we all make mistakes. Thanks again for the awesome video.
Totally agree
Great Video on test methodology. At times 14:55 and 15:50 you referred to a meter reading of 0.09 as 900 millivolts. Isn’t that 90 millivolts or am I missing something reading your meter?
i think doing a video and talking you will say the wrong thing. 0.090 is 90mv which is very good. 0.9 is 9 tenths or 900mv would equal getting bad. he just made a simple mistake trying to talk and video I've done it myself
Yes you’re correct. Misspoke there. Sorry about that. Thanks for watching!
@@theroyaltyautoservicesorry, I’m still confused. Is the correct reading supposed to be .5 or less?
yes 500mV or .5 volts@@erichkaanikin3555
When you "diagnose" a bad diode or diodes you replace them right> or do you buy an alternator?
What about on a European care like a volvo where the battery is in the trunk do you still need to go directly to the battery or can you use the designated post in the engine bay.
I guess also if you have to use a jumper do you minus the voltage drop across the length of wire you are using
Shout out to Bernie Thompson 🫡
when part 2 of the a/c?
Been there done that , condemned the alt.. Wrongo ! A broken control wire who's circuit goes through the charge gauge on the dash !😮
Thank you for the complete end to end explanation. DIYer here. I don't have a scope just a multimeter. Is it necessary for me to invest in a scope? I have relied on the multimeter so far.
The scope is a massive resource to have. Start small. You don’t have to start by buying the ATS. Have you seen our video with the 3 channel scope? Might be a good place to start for you.
@@theroyaltyautoservice I will look for that video!
How were leads set up on the alternator when you were using the Zeus for ac ripple?
Positive on the battery lug on alternator and negative on the alternator case.
An alternator can be internally shorted to a ground also and it will kill the battery even if it is charging the battery by creating a parasitic draw and usually when this happens it is a high drain in multiple amps as well so if you get a car with a parasitic drain issue try disconnecting the battery cable from the alternator if the drain goes away you definitely need an new one
Thanks , wait for more more informative lessons , test don't gess is my slogan
Test don't guess, has been used by Paul Danner (scanner Danner) for about 20 years now. Other people in the trade are now using it more, which is fine as long as they adhere to it!
@@mikeburdi3464 please don't misunderstand my comment , i mean i'm also use it , thanks
@@autoservice6572 it's all good my friend. Like I said, many people are using it now, which is fine. But we have to live by it and not just speak it. Good luck on your business, I hope you have lots of success!
What’s the maximum voltage drop on both the negative and positive post of the alternator and us this value cut across all brands
Should be in total under 0.5V, if more check for good connections and corrosion. Remember this includes both battery to alternator, and starter, plus the fusible links that are typically used, plus the ground cable from engine to frame, and the ground cable from frame to battery. most often engine ground, and battery to frame, is the one neglected, and often one is poor contact. Remove the chassis connection, clean the terminal lug, the bodywork there, and apply a thin film of grease ( white grease, dielectric grease, Vaseline, wheel bearing grease, or even gear oil or engine oil at last resort), and put the connection back, and make sure the nut is clean on the contact face as well. There are often TSB's about this, famous on GM products as they age, and covering multiple models and years. Same for the fusible links and multifuse units, undo, clean the contacts, retension for the plug in ones, and clean and reconnect both with a thin film of grease on all mating surfaces.
Could you see the ripple on an old school analog meter ( like Simpson)?
I could NEVER grasp all this by trying to learn from a book by myself. My auto shop teacher in high school could teach like this. Too bad I was only there for my freshman year.
I did not know it was possible to do an AC ripple test while testing DC voltage at the B+ terminal of alternator. Interesting! It was good to see someone else struggling with tangled leads about 13:30. I have the 10 ft. picoscope leads and have yet to find a good way to store them. Anyone have suggestions?? =)
We wire tie the 2 leads every foot which saves some tangles as it's like a thicker cable.
👌
Could the show the PCM control wave ?
It varies from manufacturer to manufacturer. Some like Fords have 2 wires going to the computer but most others have just 1 (out of the several tiny wires on the alternator connector).
Thank u teacher I just need to afford the ats oscilloscope 😅
Too many brokies to count
.. i got one that works but the Bearings squeal first start for a minute so i gotta replace it Anyway before it seizes & smokes the Belt off.. ⚡
When is A/C parts 2 is coming?
you should break the fusible link and then perform the tests with it broken.
Just a small error- .090 is 90 millivolts.
I think you might need a new camera. It’s kind of blurry. Or maybe a setting. Sorry I’m not too familiar with camera work.
I think it's just this video or maybe they used a different camera for this video.
I think I’ve seen it on every video that they put out
@@t.k5928 Maybe the outdoor location for this video made it more apparent here.
It was the location being outside that affected this video. As you can see I was trying to move around a lot to get rid of the glare. All the bays were full because the shop has been crazy busy but we wanted to get a video done. Hopefully we won’t have to do the next one outside. 😬
The name of your video is very misleading, it does not cover late model LIN controlled alternators. For example when the LIN is bad but the alternator is charging by default, the owner does not know there is an actual problem overcharging the battery and killing it over time. Changing a LIN alternator with the wrong aftermarket part number where the LIN Header is wrong and it will not talk to the ECM, this Header can be seen on a scope waveform, and in my opinion, the #1 problem with replacing alternators, the store sells the wrong application way too many times since they do not look at the LIN Header nor do they care. Can you please do another video covering such LIN examples? The overall waveform on the Alternator LIN wire will show if more than one LIN component is on that line, based on more than one Header, which is easy to read based on the first few pulses, and based on codes will point to a problem on this overall circuit, and we might see the missing Header signature of a specific component, problem found. Another reason why we need waveform captures in our customized library. cheers.
Yeah, I'll run out and buy a $20k scanner and $4k oscilloscope to replace an AutoZone $80 crap alternator smdh 🤦👎
yes sometimes that may fix it, but now the pcm is in control of the new alternators and its a digital signal being transmitted so you can get a cheap scope for that, but just replacing that cheap alternator is just a guess .when that cheap alternator does not fix it then that's when knowledge and the right equipment being used will fix it. hey its the car manufacturing doing this to you not us, we don't like what they are doing either. i do this same testing so i buy old school cars so i don't have to deal with it for myself
I understand what you're saying, but I replaced a friend's alternator in a Honda minivan and a rebuilt was $300. Everything is expensive these days.
As someone who has spent time in retail auto parts stores. Even if someone’s alternator supposedly tested bad. I would still refer them to a shop. Because of bad grounds or many other reasons. Unless it’s a bench test. So many people comes to the stores. Think the free testing is gospel. Unfortunately there’s many people who work in these stores who think the same.
Those free tests are a direction to go. Not gospel.
Doing this stuff for a living is painful and boring.
For Voltage drop, at 15:44 Technically you should be putting the probe directly on the post of the battery as well, one could have a bad connect between the battery clamp and post.
when AC Part 2 is comming?
It’s on the way! We’ve been so busy at the shop and just needed some time to catch up. Sorry!