Alternator A/C voltage question

[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

[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.

[oldskewel]

Originally Posted by Bmwe5320023.0

...
At this point he worked on the car for so long that the battery discharged and wouldn't start the car ...

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?

[Bmwe5320023.0]

Originally Posted by oldskewel

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...

[Bmwe5320023.0]

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??

[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

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