Hello there,

Anyone have any idea if this shot of the alternator in action looks good or bad?
It's the zoomed in battery voltage that results from the alternator charging the battery.
Note it's not looking like a perfect 3 phase rectification so i was trying to find a way to simulate this but nothing seems to work. Any problem introduced that i tried (like on open diode) does not produce anything like this pattern.

Any ideas?

 

Those pulses look about the right frequency to be the ignition coil current pulses. Is it a 4 cylinder petrol engine?
As the alternator is generally driven by a pulley system it is difficult to guess the alternator frequency but I would expect it to be at a lower frequency. What does it look like at a slower timebase speed?

 

Something I took...

 

A few ideas:

1. Make sure that the alternator is loaded. LIghts on - high beam; Heater fan on full; engine running, of course.
Frequency should change with RPM. There's a tab on some alternators (very hard to get to), that when shorted to the chassis will cause full output. That was the regulator test. The tab can be seen in this AC Delco regulator. https://www.dbelectrical.com/produc...delco-10si-12si-15si-17si-27si-8040-6240.html


2. Another test. Locate the fat, usually red, wire from the battery to the alternator. That wires usually comes out of the side attached to a stud. A voltmeter (mV) used ACROSS that wire will act as an ammeter with an unknown resistance. So, that value will change with load.
Record this value and conditions when the system works for future use.

These are my usual tests, combined with a hygrometer test.

Big battery failure issues are usually caused by no use, deep discharges, failure to replace electrolyte, times up (7 years).

Alternator/battery issues: loose cables when service is done to the car that requires removal, poor installation, Poor contacts, Contact corrosion (Never happens anymore with the red/green pads on the posts.

On the number of vehicles my parents and I had (Alternator only issues):
1960's Chrysler: external regulator; bad bearing; brushes; insulation breakdown (replaced) (about 17 year ownership)
1960's Ford - No issues
1960's Chevrolet (Can't remember)
1970's Chevrolet: Rotor weld/solder broke; Bulkhead connector coroded; internal regulators replaced
1970's Chrysler; ECM did regulation - no issues
1980 Chevrolet - No issues
2000 Chevrolet - No issues, 16 year ownership and counting
1980's Toyota: Car was painted - cables not tight, loose connections, regulator soldered in place, replaced alternator;
replaced a battery cable as well at some other time. (17 year ownership)
2000 Toyota: No alternator issues 16+ years and counting.

In a few cases, jumps were made by loosening the positive on the failed car; jumping and putting it back. This isn't recommended.

The Toyota had the worst issue. Sometime in a January, I did a hydrometer check and I though the battery was bad, The car had little use that winter (e.g. 6-8 weeks idle). In May, I asked the dealer to check the battery and the battery was deamed OK, A few days later, i took it for a 40mile trip. Car died AT my destination and would not start right away. Came out after 45 minutes and the car started. i got to a second destination and things didn't seem right. I did my thing for another hour and called the tow truck. dx: belt broke. The replaced belt and charged battery and said it's OK. Two days later, no start. Jumped and took to dealer and they replaced battery.

Battery university basically doesn't trust electronic tests. Hydrometer is better. The repair companies don;t even own a $4.00 instrument. Probably too dangerous?

When the rotor wire broke, that was a "complete die" with no warning and no idiot lights.

One Toyota had a voltmeter and an idiot light. This may have been the nicest set-up.

Some parts shops have the ability to do an "off vehicle' alternator test.

The older alternators had the diodes pressed in (Top Hat) and seemed to be very reliable. The early Chrysler alternator had brushes at right angles which was nice.

 

I set off on a long journey and discovered that the radio would only work when the engine was running at low revs, complete silence otherwise.
I carried on.
While travelling I often seemed to come behind a vehicle making a burning smell.
I arrived and parked no problem.
When I wanted to leave again the starter barely turned over the engine at all - wouldn't start.
Called the rescue company. They jumped it and started the engine and measured the battery voltage - 19V
The alternator regulator was duff and now the battery was cooked.

It turns out the radio doesn't work when you supply it with 19V and the smelly vehicle was mine!
I have now fitted a voltmeter! (stable door and all that)

 

@AlbertHall Too bad you did not get cooked

 

Those pulses look about the right frequency to be the ignition coil current pulses. Is it a 4 cylinder petrol engine?
As the alternator is generally driven by a pulley system it is difficult to guess the alternator frequency but I would expect it to be at a lower frequency. What does it look like at a slower timebase speed?

Hi,

This is actually a 5 cylinder, 20 valve engine, but i did not expect this to be this difficult. I expected to see at least something that resembled a three phase rectified system waveform but what i see is something like that but with some differences. I have to do more testing i guess. The engine was at about 1500 rpm at the time of that scope pic.

 

A few ideas:

1. Make sure that the alternator is loaded. LIghts on - high beam; Heater fan on full; engine running, of course.
Frequency should change with RPM. There's a tab on some alternators (very hard to get to), that when shorted to the chassis will cause full output. That was the regulator test. The tab can be seen in this AC Delco regulator. https://www.dbelectrical.com/produc...delco-10si-12si-15si-17si-27si-8040-6240.html


2. Another test. Locate the fat, usually red, wire from the battery to the alternator. That wires usually comes out of the side attached to a stud. A voltmeter (mV) used ACROSS that wire will act as an ammeter with an unknown resistance. So, that value will change with load.
Record this value and conditions when the system works for future use.

These are my usual tests, combined with a hygrometer test.

Big battery failure issues are usually caused by no use, deep discharges, failure to replace electrolyte, times up (7 years).

Alternator/battery issues: loose cables when service is done to the car that requires removal, poor installation, Poor contacts, Contact corrosion (Never happens anymore with the red/green pads on the posts.

On the number of vehicles my parents and I had (Alternator only issues):
1960's Chrysler: external regulator; bad bearing; brushes; insulation breakdown (replaced) (about 17 year ownership)
1960's Ford - No issues
1960's Chevrolet (Can't remember)
1970's Chevrolet: Rotor weld/solder broke; Bulkhead connector coroded; internal regulators replaced
1970's Chrysler; ECM did regulation - no issues
1980 Chevrolet - No issues
2000 Chevrolet - No issues, 16 year ownership and counting
1980's Toyota: Car was painted - cables not tight, loose connections, regulator soldered in place, replaced alternator;
replaced a battery cable as well at some other time. (17 year ownership)
2000 Toyota: No alternator issues 16+ years and counting.

In a few cases, jumps were made by loosening the positive on the failed car; jumping and putting it back. This isn't recommended.

The Toyota had the worst issue. Sometime in a January, I did a hydrometer check and I though the battery was bad, The car had little use that winter (e.g. 6-8 weeks idle). In May, I asked the dealer to check the battery and the battery was deamed OK, A few days later, i took it for a 40mile trip. Car died AT my destination and would not start right away. Came out after 45 minutes and the car started. i got to a second destination and things didn't seem right. I did my thing for another hour and called the tow truck. dx: belt broke. The replaced belt and charged battery and said it's OK. Two days later, no start. Jumped and took to dealer and they replaced battery.

Battery university basically doesn't trust electronic tests. Hydrometer is better. The repair companies don;t even own a $4.00 instrument. Probably too dangerous?

When the rotor wire broke, that was a "complete die" with no warning and no idiot lights.

One Toyota had a voltmeter and an idiot light. This may have been the nicest set-up.

Some parts shops have the ability to do an "off vehicle' alternator test.

The older alternators had the diodes pressed in (Top Hat) and seemed to be very reliable. The early Chrysler alternator had brushes at right angles which was nice.

Hi,

Yeah, what i did was turned the lights on but forgot that the load from the headlights is not that much really. So i will repeat the test again soon. Thanks for all the info.

 

Something I took...

View attachment 120358

Hi there,

What are we looking at here?
I see a bunch of waves, look like inverted diode conduction waves in a rectifier but why inverted.
Maybe you can explain this scope shot a little more which i think would help a lot.

Thanks.

 

Mr Al:

Your not too far off, but your digitizing is choppy: See here: https://www.picoauto.com/library/automotive-guided-tests/alternator-ac-ripple-diode-test/

You could have some pick-up noise.

What you don;t have is straight lines every 3 peaks which in indicative of a shorted diode.

Althogh, these http://jaguar.professional.org/Alternator.php guys beg to differ. Clean is better.

 

Mr Al:

Your not too far off, but your digitizing is choppy: See here: https://www.picoauto.com/library/automotive-guided-tests/alternator-ac-ripple-diode-test/

You could have some pick-up noise.

What you don;t have is straight lines every 3 peaks which in indicative of a shorted diode.

Althogh, these http://jaguar.professional.org/Alternator.php guys beg to differ. Clean is better.

Hi,

Yeah i was looking for that dead spot and didnt see it, but the waveform was so messed up i did not want to assume anything just yet.
I agree there could have been noise pickup messing up the signal and therefore making it harder to analyze. Maybe i'll have to shield the little scope board or something.

Next time i do the test i will have the lights and heater on. The heater takes a lot of current in this car so that will help i think although i dont know how much noise it may add to the signal (the motor turning of course).

I probably should have taken the reading right across the battery right at the terminals instead of at the OBDII connector. It's easier to do with the connector though because it was cold outside and the connector is right inside the car for easier access. Plus this little scope i have has to have the battery pack plugged in and so the whole setup had to sit on something non conductive. I should probably put that into a plastic box.

What bothered me most about the waveform i did see was that there were noticeable "double humps" which makes me think that maybe one diode could be weak or something, because it is almost like the missing hump wave where one diode is bad. But in simulation i was unable to come up with a combination of bad diode(s) in order to get the same or similar waveform.

 

This is an idea I have never tried. Energise the rotor directly ( Not via the regulator.) with a low voltage (2 - 4 volts Or from 12 volts via a resistor say 10 ohms.) Disconnect the output of the alternator and load it with a resistor ov about 20 ohms ( 4 to 50 ohms should work.) Run the engine and monitor the alternator output with the scope. I think this should show the clean rectified output and I think shorted diodes should show up on the waveform.
Les.

 

Hi there,

What are we looking at here?
I see a bunch of waves, look like inverted diode conduction waves in a rectifier but why inverted.
Maybe you can explain this scope shot a little more which i think would help a lot.

Thanks.

It's a shot I took at the out put of a car alternator running at idle.

 

This is an idea I have never tried. Energise the rotor directly ( Not via the regulator.) with a low voltage (2 - 4 volts Or from 12 volts via a resistor say 10 ohms.) Disconnect the output of the alternator and load it with a resistor ov about 20 ohms ( 4 to 50 ohms should work.) Run the engine and monitor the alternator output with the scope. I think this should show the clean rectified output and I think shorted diodes should show up on the waveform.
Les.

Hi there Les,

Good idea, but i am afraid that it would require too much work on my part when i want to test the alternator which would be periodically like maybe once every 6 months or once every 3 months or something like that. But also there should be a way to do it without having to disconnect the alternator wires and play with the loading and stuff like that. I believe there is because i know other people do it that i have read about, but their waveforms look a little different than mine so i had some questions about it. Scopes are sensitive enough to pick up the small changes that occur to the battery voltage which should be telling of the state of the alternator and possibly battery too.

It would have been nice to see some more scope pics of other people's cars but i only found so many on the web so far.

 

This may be a better educational pic: https://www.circuitspecialists.com/blog/testing-an-alternator-with-an-oscilloscope/

There are some cars out there that have some really smart chargers that apparently do some load shedding.

 

This may be a better educational pic: https://www.circuitspecialists.com/blog/testing-an-alternator-with-an-oscilloscope/

There are some cars out there that have some really smart chargers that apparently do some load shedding.

Hi again,

I had read that but was unable to come out with anything conclusive about my own waveform from that information.
My wave seems to be somewhere in between a good wave and a 'bad' wave. Mine is just the ugly wave

 

I think the output of the alternator is controlled by PWM of the current through the rotor (Field coil.). It is possible that you could see the PWM frequency superimposed on the rectified three phase waveform which could give confusing results.

Les.

 

The load on the alternator just looks too low to me.

You do have to look at all of the pieces with DC voltage/regulation on the top of the list. Output current at some known load and for that matter, if some sort of "smart charging" is employed.

Without a way to force maximum output *screwdriver on some alternators), it becomes difficult. Max output generally would test the regulator if everything else works. Partial load tests, should reveal diode issues.

Not really sure what a totally broken rotor would revel except no output with the regulator bypassed. Ripple height usually increases with load.

This "drive by wire" stuff makes it difficult to move the accelerator in the engine compartment. No experience yet.

Grounded stators where the insulation has broken down is another failure and so is insulation breakdown on the rotor.

On the latest vehicles, it just became is it the ALTERNATOR, BATTERY or BOTH because rebuilding the alternator wasn't feasible.

 

I think the output of the alternator is controlled by PWM of the current through the rotor (Field coil.). It is possible that you could see the PWM frequency superimposed on the rectified three phase waveform which could give confusing results.

Les.

Hi Les,

Yeah unfortunately that is a possibility. I am hoping i can make some sense of this eventually anyway though.
So now i see more clearly why you suggested disconnecting the alternator. That's a little too hard to do though on this particular car. On my old Hyundai that would have worked much easier as that was such a simple system.
I am not even sure if the ECU controls this alternator or not on this more modern car.

 

The load on the alternator just looks too low to me.

You do have to look at all of the pieces with DC voltage/regulation on the top of the list. Output current at some known load and for that matter, if some sort of "smart charging" is employed.

Without a way to force maximum output *screwdriver on some alternators), it becomes difficult. Max output generally would test the regulator if everything else works. Partial load tests, should reveal diode issues.

Not really sure what a totally broken rotor would revel except no output with the regulator bypassed. Ripple height usually increases with load.

This "drive by wire" stuff makes it difficult to move the accelerator in the engine compartment. No experience yet.

Grounded stators where the insulation has broken down is another failure and so is insulation breakdown on the rotor.

On the latest vehicles, it just became is it the ALTERNATOR, BATTERY or BOTH because rebuilding the alternator wasn't feasible.

Hi again,

Yes i intend to check this again with more load this time. I am hoping to get a more understandable scope picture.
Originally i though it would look just like a three phase rectifier system but this turned out to be a little more tricky than that.
I also thought about applying a heavy resistive load which would draw a lot of current from the battery and alternator. Not sure if that is a good idea though as all i have in my possession at this time is a 100 amp resistive load. It is made for testing the battery when the car is off, not while running, so i dont know if it will hurt the system.