Alternator A/C voltage question

[eskirvin]

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.

[Bmwe5320023.0]

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

[AV8R4AA]

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.

[Bmwe5320023.0]

some hood humor is in due course for this thread

[Bmwe5320023.0]

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

[Bmwe5320023.0]

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!

[andrewwynn]

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

[andrewwynn]

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

[Bmwe5320023.0]

Originally Posted by andrewwynn

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

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:



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.

[Bmwe5320023.0]

Originally Posted by andrewwynn

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

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