Alternator A/C voltage question
 

I'm trying to diagnose a nagging alternator whine with a new stereo install. Checking if the alternator is causing issues or not.
I've been trying to solve this for months and can't figure it out
https://www.diymobileaudio.com/threa...3#post-6033045
I'm trying to figure out if I should be a new alternator.

I just wanted to compare the readings and see if mine are out if whack.

I set the multimeter to AC, positive to alternator stud, negative to the battery or ground.
I'm getting a reading of about 0.150V AC

What I'm trying to find out is if this reading is normal or if I need a new alternator.

Meter should be on DC voltage to start.with load on engine ,should be around 14v dc.

Sent from my SM-G781W using Xoutpost.com mobile app

You can check DC voltage the 2 jump start locations under the hood.

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Trying to measure alternator ripple with a multimeter is pretty much futile. Scope is much better for that but if your alternator is otherwise fine and previous stereo was working fine it's very unlikely the alternator is at fault.

Ahhh I see. Was told on audio forum that the AC is too high and I need to chance the alternator as it's causing the alternator whine...

While in general terms, that may be the case, its a bit more complex than that!

The Alternator generates an AC voltage, which is rectified (turned into DC) and regulated (to around 14.4volts) by the regulator/rectifier. The output should be pure DC (no AC) but in the real world there is always a small AC component in the main output. It is this residual AC that the audio chaps are likely referring to but if this issue started when you changed the stereo, the alternator is not likely the problem - the problem is either within the new stereo or related to the wiring of the new stereo.

How is the new stereo earthed (the return path for the supply voltage)? A poor earth can reveal alternator whine.

Also, is the whine present on all sources (radio, etc.) or only on a source external to the stereo itself?

The interconnects (usually RCA cables ) can be a huge problem especially if you have long runs. Try using some different ones. I used to make my own with twisted pair, foil shielded cable. The shield should be grounded only only the source end of the cable. If the head unit has adjustable or switchable output level then going with the higher level and turning down the gain on the amp can be a big help in at least diagnosing the problem.

The amp is grounded on the ground stud in the trunk. Same stud where the battery negative terminal is grounded from factory. I tried 3 different RCA cables. If you have a suggestion which RCA cables to buy, please let me know.
Noise is present for Bluetooth, am and fm. These are thebonly sources of audio I have.

So you have an external amp connected to a head unit via RCA interconnects?

You most llely have a "ground loop" - a situation where multiple ground paths exist, with a potential difference (a small voltage difference) betwen the ground locations.

These can be tricky to fix - you could try lifting the ground (shields) from the RCA cable to the amp (at the amp end only) - so that only the centre connection (carrying the audio signal) is connected.

Yes, I have two amps, one for speakers and one for sub. 4 crossovers, 4 speakers, 4 tweeters.

Yes I figure I have a ground loop, but unable to find it. That's the tricky part, nobody seems to be able to figure out how to locate the ground loop.

Your suggestion lifting the ground portion of rca cables is interesting. I never heard if before. I need to bend them away? I guess this would destroy the rca cables for future use?

I've just ordered an alternator filter just in case.
Just to rule out any ripple effect from the alternator.
Kinda expensive but I don't have too many ideas. I just want to fix this problem
https://www.wmjmarine.com/150a.html

No need to destroy your RCA cable - grab two RCA plugs and two RCA sockets from RadioShack and wire them with only the centers connected (not the earths).

Or grab one of these...

https://m.media-amazon.com/images/I/...SR320,320_.jpg

https://www.amazon.com/dp/B000LP4RMG?th=1

Ohh I see. Tried them, the didn't do much.
https://i.ibb.co/MkVdr0B/20220530-193937.jpg
https://i.ibb.co/JB2HnMy/20220530-193942.jpg

Still worth trying the half-wired RCAs - something is causing the whine! :-)

Something definitely is. I ordered two of these
Jensen Transformers Iso-Max CI-2RR

And also ordered Newmar 150-A Alternator Filter to rule out any ripple issues.

I'm not sure I totally understand how to try your suggestion with rca sockets and plugs. Do you have a video or image demonstration?

Simply take an RCA plug and socket and solder a wire from the centre pin on each to the other - don't do anything with the earth connections.

Make two of these.

Now unplug the RCA cable from the amp's input, insert the RCA plugs (you just made) into the amp's inputs and then plug the RCA cables (from the HU) into the sockets.

You now have a signal path from HU to amp (for left and right channels) but the RCA cables are ONLY earthed at the HU end (not at the amp end).

Might help...

BMWE. I was scrolling the thread on page 1, going to page 2 to put my reply.....
The Jensens' should resolve it for ya.......in this chassis, I ran a full Alpine F1, Focal BE --- etc with Genesis amps.

Ohh now I see what you mean...

It would be way easier and cheaper to just buy cheap rca cables and destroy them than buying sockets and plugs and soldering them together! :)

That would be great! Ordered two Jensens and 150 amp alternator noise filter. So at least alternator ripple will be rules out.

It terms of Jensens, I don't know if they will work.
Here's what I've been told on another forum:

Since you can hear the 'whine' (noise) out of your speakers, it has already become part of the audio-band signals, filtering the audio output RCAs (if you have any to begin with) means the whine cannot be filtered OUT without also filtering the audio signal.

Not here - plugs/sockets are WAY cheaper than even the cheapest cable - but yeah, what ever works. :thumbup:

Key thing here is the "lift" the earth connection from the RCA connectors at the amp end - not the HU end.

Same goes for the earth loops isolators you show above - they will work best when fitted close to the amp (directly on the amp inputs) - not close to the HU.

Yes I tried the isolators at the amp end.
I will try the rca cables tonight and will include the pictures.

Yeah I can buy a set of rca cables for like 10-20 dollars with next day delivery!)

So no one seems to mention it, there's two types of cables.
Twisted pair and insulated rcas. My extra spare rcas I use are actually twisted pair. But I may have some insulated too. They're both expandable. I'll include some photos.

Someone also suggested on audio forums that spark plugs and coils can cause problems so I ordered a set of Denso.

https://i.ibb.co/ggwhptj/20220605-132957.jpg https://i.ibb.co/Z60VXPX/20220605-132846.jpg

No change at all in whining. I made sure no ground touched the plug on the amp.

Gotta be something else

Does the amp output a "whine" with no inputs connected?

No whine if rca cables are disconnected.
However there's whine if rca cables are only connected to the amp, not the headunit.
Latest theory is that rca cables function as antenna and pick up noise from possibly bad spark plugs and ignition coils, even though I have no misfires or codes.

Get some foil shielded cables with the shield grounded only on the source end (some will have arrows on them to direction) or make your own, or try the isolators you have in the picture.

Do you have a link to the cables you recommend?

The isolators in my pictures, I already tried them. No change.

Got the plugs and boots today.

I guess I thought coils came together with boots, but I must've not realized this was not the case.

I replaced boots and spark plugs.

My old spark plugs were totally drenched it oil. Boots as well, and bottom of boots were kinda missing. Old plugs were gapped at 0.6 instead 0.4. I can't understand how this happened. I've replaced the cover valve gasket and spark plug gaskets as well before.

I guess I need to redo valve cover gasket to see what's going on there.

At this point I just wanted to see if the whine would go away.

Started the car, no luck. Whine is still there.

Withing 10-20 seconds the smoke filled my garage really bad, I turned off the car.

There must be a really bad leak that must've caused the oil burning with new spark plugs and boots.



I guess next step is to buy new coils and see if it helps. Obviously gotta redo the valve cover gasket. I'm pretty adamant I did it well a year ago, but the leaks on spark plugs are proof to the contrary.

https://i.ibb.co/qFrTFF3/20220606-150832.jpg https://i.ibb.co/MGfXZGZ/20220606-163258.jpg https://i.ibb.co/HT0W0C5/20220606-170702.jpg https://i.ibb.co/qFXYpjz/20220606-163335.jpg https://i.ibb.co/0DzGGCg/20220606-171945.jpg https://i.ibb.co/0rLrJVD/20220606-173520.jpg https://i.ibb.co/n1Td813/20220606-173530.jpg https://i.ibb.co/8P7fHmt/20220606-173536.jpg

What's the best brand for coils,
Delphi, nkg, brewing?
I can't find any coils by denso

Do you have any plug in accessories? In my e53, I couldn't tune the radio when I had my USB plug in to charge my phone. The DC> DC power adapters are notoriously bad for creating radio interference or audible hum.

Make an audio recording or scan witg FFT program to figure out what is the frequency.

Andrew my stock audio is completely removed, including wiring, amp, sub, oem HU, speakers, radio antenna on the trunk door, everything.

So it's a completely new installation where I connect to the headunit via Bluetooth

Can you tell me.mpre about scanning with FFT?
Never heard of it before

Mine has NGK and single tip Iridium plugs. A NGK coil set from Summit Racing goes for $140.99. #NGK-49177 After putting them in and running it, the range went above 500 miles! I think it maxed out at 525+ miles! So it did see a difference from old stock worn out coils. Three were original. Three were replacements. #3 was failing intermediately so I replaced them all.

Nice results! Looks like NGK is still very reputable.
I think my Denso boots are good quality.
I just ordered Delphi ignition coils from rockauto, I read online that bmw changed their oem for coils from Bosch to Delphi due to issues with Bosch.
Will see if coils help with the whine...
Don't know if there's any difference in quality between Delphi, NGK and Bremi. I was gonna order Denso coils but realized Denso doesn't make coils, only boots

New spark plugs, boots and coils didn't help with the whine.
Next idea is to try Newmar 150-A Alternator Line Noise Filter 150 Amp
Ordered it on June 1 from USA and still waiting.
I think it should be here in a couple of days finally.
Shipping to Canada takes longer than if i order on aliexpress lol!

If someone can measure their A/C voltage out of the alternator, I'd really appreciate it! Will tell me if I need to consider replacing the alternator!

Just on the off chance...

I had a similar problem and it was actually the radio function running in the BACKGROUND since these units go all over the world the radio station frequency ranges alternate between compatible and not, giving you a guaranteed static channel every 1/2 megahertz or something.
I deleted the automatic radio start up and haven't heard it since.

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Every multimeter will give you a different and inaccurate reading so measuring isn't going to help much. You have the new low noise alternator coming so you might as well use it. :dunno:

I can grab an oscilloscope and get a screen-shot of the output waveform but unless you can do the same, it won't help much. :rolleyes:

A good DMM will show two things: 1) the AC over dc
2) the frequency.

When one of the three diode banks starts to fail you will get a much larger AC component, that's what's being asked here.

If you want to eliminate AC interference from radio simply remove the serpentine belt. No alternator no hum

I actually deleted the radio module from the vehicle completely, as well as the antenna. I think it's not possible to have a radio at all in the car anymore! :)

If you post your oscilloscope, I'll gladly buy the same make and model and repeat the test! :)
I feel with how deep I got into DIY stuff with my cars, owning an oscilloscope would not be unreasonable !

Exactly Andrew!
I'm just trying to get some values to compare.
To know if diodes, rectifiers etc. are bad in my alternator.
I mean it's not a big deal to buy a new alternator and test it out this way, by just swapping the parts.
But for me the spirit of this forum is to learn how to test components, instead of just going through replacing parts mindlessly. I mean it won't hurt my car to get a new alternator lol...but would be nice to at least have some measurement to compare.

FWIW, it's a Fluke 123 Scopemeter but any 'scope will produce the same test results - even a cheap add-on for a smart phone.

https://i.ebayimg.com/thumbs/images/...n3T/s-l200.jpg

https://www.amazon.com/Oscilloscope-.../dp/B07TB8V2X1

Ok so I installed newmar 150 amp alternator filter.
It did not help with the whine.
I'm wondering if it's possible for ripple to be getting through the filter?
So far I can only measure AC, but you guys are saying it's unreliable.

I can easily order the oscilloscope
Can it indicate anything else other than alternator being the issue?
Let's say I buy oscilloscope and it shoes ripple, how does it help me?
What if I just buy a new alternator right away.
Let's say new alternator doesn't fix the problem.
Would oscilloscope be useful? What would be my next step?

You seem to be making the assumption that the whine is caused by AC from the alternator - which is correct in a way but all alternator outputs contain *some* level of AC. Most audio systems are capable of rejecting this AC - but your current audio/amp/wiring configuration is not.

It could be the AC level is too high or it could be the wiring configuration you have.

An oscilloscope is useful for viewing the waveform (shape) of the AC on the alt. output and can give clues as to the fault source but there are other way to diagnose the alternator diodes. You can measure the diodes with a multi-meter to verify they only conduct in one direction etc. but you need to open up the rectifier/regulator to do this.

The test you performed prior to your first question in this thread is the other simple test. Your result of 150mV of AC seems rather high - anecdotally, 50-100mV is normal but it can spike higher under load. Not knowing the charge state of your battery or the other factors affecting the electrical load on the alternator at the time, it's hard to say if 150mV is a problem.

How much AC is on the jumper terminals now that the filter is in place?

I ordered a brand new alternator, it's just easier this way. Getting here tomorrow.
If I measure AC before the filter, it's showing 0.227. Right after the filter, it's 0.116.
If I measure on the battery terminals, it's 0.017

I'm also suspecting my 2 amps are both defective.
I'll add more details if I don't get anywhere soon.

Since we are beating on charging systems (Alternators, Regulators, Wiring, etc), I changed out my alternator on the X5 4.8is as it slipped into a zero charge state. Painful process until I finally figured out that the aux fan (pusher fan) just unsnaps and pulls straight up without any issues. Man, does that make the process of replacing the drive belts, idler, and tensioners easy as well as exposing all the mounting bolts on the alternator. I know I am slow...

After completed I did a little testing on what happens when the grounds and positive cable points are loosened. The charging drops to ZERO volts (Battery voltage only) the minute any one becomes finger tight.

The reason I am mentioning this is to provide a field testing confirmation that if you are having charging system issues (battery light flicker, battery draining while driving, voltage flux while driving, etc) you should first unbolt and CLEAN all the connections along the grounds and positive cable points from the battery to the alternator INCLUDING the jump points under the hood.
Then check the alternator/regulator itself.

Thanks Stephen!
I unbolted every ground point and cleaned them, did the same with positive. This picture you posted is for V8 (which is correct for your X5) but I think i6 is very similar, just the alternator and the starter are on the same side.
People say not to run the rca cables parallel with power cables. Funny that X5 has power cables running on both sides. I did run my rca cables in the middle!
I cleaned every ground point and positive with 80 grit sandpaper until it was shining. Installed new alternator, oem bosch. For good measure also sanded the points where alternator attaches to the bracket.
Now what I want to see, if there's difference in AC current with the new alternator. At least it will tell me it there was any point replacing the alternator. But this is just for curiosity's sake.
I didn't buy o-scope yet, but I don't know how it will help me. If it will show me something, it's not really actionable information. The best I can do is buy a new alternator, which I just did. So no matter what I measure with o-scope, I can't do anything more. I installed new alternator and installed expensive Newmar alternator filter. I also ordered another filter, Helix Cap 33, it was recommended to me but someone who had the same issue and that filter solved it. I plan to install it just before the amp power, to clean up any possibly remaining interference.

Brand new alternator, brand new amp, SAME OLD WHINE.

If you want to DIY then why not make your own cables? Foil shield is better than braided, twisted pair with the shield grounded at the source (but you could try at both ends as well)

Might be worth testing to see if the whine is in the audio leaving the source (H/U).... :dunno:

And/or try powering the amp from a separate (spare) car battery, just as a test.

I do not want to DIY anytning at this point lol!!
Make rca cables? Why not?
I dont know, it's another variable that I can screw up...
Are we at a point in 2022 that DIY rca cables would be better than what's commercially available from professional audio stores etc? In an industry that developed and matured over decades
I've been trying to get this fixed for more than a year, I just want it to work. I don't really want to learn how to fabricate audio cables at this point lol. I don't even know if rca cables are the issue at all

It's my second head unit.
I can try powering the amp with another battery, though I don't have one, but this is my 3rd amp

This whole thread just hurts. So much money spent for a good experience that the user certainly isn't getting, from his perspective.

A number of people in various threads on too many forums to count, install stereos from trusted brands only to find out they've got grave design flaws. So much is designed by these companies and sent to China to produce. I don't know if these companies QC it afterwards, but it sure seems many don't.

Try grounding the negative lead of your RCA cables to the same ground your device is connected to. For the source, ground those leads at the same point the source unit's power is grounded. For the amp, ground them where the amp is grounded. Do it for the source first, check if the whine is reduced or gone. Do it for the amp, check if the whine is gone or reduced, and then try it for both at the same time and see if the whine is reduced further, or gone. If any of these steps you've taken temporarily works, make them permanent.

You can't build your own radio, so bandaid solutions may be all you can commit to. If it gives you the sound you desire, make it permanent. I've got an Xtron Android head unit in my E53 and the whine was initially awful until I committed to grounding the negative of the RCA output leads to the same ground as the head unit. The whine is only noticeable now if there's no music playing and I'm at a stop allowing me to rev the engine.

Also, I don't remember reading it in this thread, but if you used the "stock" ground for your head unit, I'd suggest making your own.

Thanks for your support buddy!:)

If you think this thread hurts, take a look at these :)

https://www.diymobileaudio.com/threa....448099/page-7

https://audiosciencereview.com/forum...4#post-1233123

I'm just trying to stay positive :)

I'm on my third amp, so i doubt it's the problem lol
I think I already tried grounding all rca ports on the headunit together and grounding them to rca cables.

Right now I ran an extra ground cables from the headunit back to the trunk, and grounded it at the same stud where the amp is grounded
I guess as per your suggestion, I can just connect one rca cable out of 4, and ground the outside of that rca cable where it plugs into headunit and into the amp?
It's a bit tricky attaching wires to the outside of the rca cables lead.

So I'll try grounding rca cable to the ground to amp/headunit and see if it changes anything.
Thanks your your suggestion

Sometimes when my wife or teenagers are in the car I hear the same noise.
It’s a high pitched noise that I know is either going to make me mad, or cost money.

:thumbup: some hood humor is in due course for this thread:bustingup

I got the tech working for 5 hours on the vehicle right now lol. When he showed up and saw the alternator and rpm make the whine, he said the new alternator is bad and I need to replace it. He said he had cases when the brand new oem alternator was making noise, and aftermarket rebuilt alternator fixed the issue. I said ok, how are you testing it to condemn the alternator lol? He doesn't have an oscilloscope. Like for real, both alternators bad and even with Newmar amp filter??
He tried a different amp, different speaker, all the same results.
Thankfully there's a loud static noise when the ignition is on, without starting the car. So that rules out the alternator...

Basically it looks like there's some kind of a short somewhere. We tried powering the system without turning key to on, and it doesn't make any sound.
There's some short somewhere for sure.
We tested resistance between headunit and metal bar under the dash, it's 0.
Then it I turn the key to "ON", that resistance jumps to 30 omnhs. Gotta find that short.
Some component that is activated by the ignition is grounding onto the vehicle ground. With higher rpm more amperage gets sent to the ground, and the ground loop gets worse.
That's my theory for now. Gotta look for that short with ignition on

When I turn the ignition is

Well the tech worked for 12 hours straight and no luck.
We're still where we started. Disconnected head lights and tail lights.
It does have something to do with headlight switch.
When turning the knob on headlight switch, the sound gets worse.
He fixed all the issues he could find, fixes whatever shorts the car had and removed a bunch of remote start wiring. Still, the whine is strong and clear.
I'm out of ideas...I thought maybe I'd get lucky cuz it was my birthday, but no luck!

BMW uses PWM for setting voltage levels; set your dash to full brightness and see if things change.

Do you have a voltmeter that shows duty cycle? If not at least measure ac on any lines that should be DC.

If you are using a "12v" line to power something you are likely tapped into a 14.4v line that is chopped up into 83% on 17% off. That would definitely cause terrible hum

What is the frequency of the whine? If a little math (pulley size ratio and rpm) you can figure out if the frequency is 3x the rpm of the alternator or same speed that is very helpful. Also: did you test with alternator disabled via serpentine belt removed? That's the surefire way to figure out if from alternator

Yes the noise and static was getting worse with turning on the switch dial.
I do have a multimeter with duty cycle but haven't tested with it yet.
I wired the relay in the following way:

https://i.ibb.co/sgmqn5Y/Screenshot-...or-Samsung.jpg

Not sure if it was a bad relay or if that wire was using pwm and causing issues.
The fact that the whine was getting worse with turning on the headlights led the tech to believe the noise was caused by headlights, fog lights etc. He disconnected them all but nothing changed. I think at this point it wasn't actually a whine but rather a high pitched static.
At this point he worked on the car for so long that the battery discharged and wouldn't start the car, so whine issue could not be verified.
He kept working on that light switch for hours, trying to wire things up with another relay etc...
In the end he couldn't fix the problem.
So yesterday I just wired it back as per factory.
If there's a possibility the relay was causing problems, I really don't need those parking lights when car is remote started.

I'm not sure how to measure frequency in this case, but I did run the car with alternator power cable disconnected, and the whine was gone.
Which still does not condemn the alternator and doesn't preclude an electrical issue somewhere else, which just gets exacerbated by increase in voltage, caused by higher rpm

I don't want to be too harsh, but you might want to factor that error into any confidence you have in anything this professional did or concluded. First day on the job?

I saw many many issues with his what he was doing and did not call him back to "finish the job". He wanted me to get a new LCM etc...

Alright so I got a second set of rca amazon basics cables. I was like, ok, I'm gonna connect these cables and the whine is gonna be there, so then I'll connect my old cables on one end, connect Jensen transformers in between, and connect amazon on the other end.

UNBELIEVABLY, the whine disappeared with only amazon cables!

I just disconnected old rca cables and connected Amazon cables running over the carpet of the vehicle.

Amazon Basics 2-Male to 2-Male RCA Audio Stereo Subwoofer Cable - 8 Feet https://a.co/d/glWWCzi

BOOM!

Whine is gone. Plugged back old cables, whine came back. Plugged amazon cables, no whine. Turned gains on the amp to MAX, no whine.

Holy moly, so much frustration, money and time and I'm 100% certain the issue is rca cables.

Now, I don't know if the issue is bad cables or interference. Now lots of people will rightfully think that I have mentioned that I tried another set of rca cables. And that's correct. The only problem, one set of rca cables I tried was twisted pair. I didn't fully know or understand this term, nor could I tell the difference by looking at them.

So that's why the previous test of substituting rca cables was invalid. I was using the wrong type of rca! I used rcas from this amp set

KnuKonceptz Bassik 0 Gauge Complete Amplifier Installation Amp Wiring Kit with RCA https://a.co/d/4Pd4Fnu

And they're twisted pair, no good!

The cables running under the carpet are Fospower

FosPower (7.6m / 25ft) 2 RCA M/M Stereo Audio Cable [24K Gold Plated | Copper Core] 2RCA Male to 2RCA Male [Left/Right] Premium Sound Quality Plug https://a.co/d/iGHF7Oh



Based on Amazon reviews, these cables seem fine, but who knows...



Just to avoid any further problems, I want to run new rca cables through the headliner!

I ordered longer cables, MonoPrice. Seems to be decent quality.

Monoprice 105348 15-Feet 22AWG Premium 2 RCA Plug to 2 RCA Plug Audio Cable, Black https://a.co/d/aRa3Fsl



15 feet should work for my idea

I drew a red line with how I plan to run them.

I haven't heard anyone running rca cables under the headliner, but why not??


https://i.ibb.co/4FNZPd1/20220707-143102.jpg