alt whine 2 amps
 

my car has had alternator whine for 10 years and im finally too annoyed with it. i have a second battery and 2 amps in the trunk. i have tried many things before this post. is it something to do with unibody and alternator being grounded thru the case? i have 1 amp for the component speakers, and 1 amp for a sub. amps are stacked ontop of eachother.
-cleaned up speaker wires near + wire coming from front of car
-moved rca from pass to driver side
-moved grounding location for one amp from the second battery, to bolt on battery holder frame (point A)
-rerouted +/- wires to pass thru trunk mat
-probed ground points A&b and got 3.5mV
-unplugging rca from amp makes no difference in whine
-hooked phone directly up to amp with rca to 3.5mm, no difference.
https://cimg6.ibsrv.net/gimg/www.sat...839b8f3199.jpg



https://cimg2.ibsrv.net/gimg/www.sat...f6f2d77e2e.jpg

I reread my answer below and realized it might come off as a lecture on how all this seemingly works. I'm not trying to insult anyone's intelligence. I've taught electronics in my past, and I guess the information just comes out teaching style. No offense intended.

The source of the whine is from the result of what's coming out of the alternator. The rectification process is only as good as the circuitry doing the rectification and the filtering of the output. The whine you hear is from a small AC component riding on the DC voltage.
No alternator will rectify and filter this AC signal perfectly, but I must believe that some will produce an output with less ripple than others. Or you may have a bad diode in your alternator causing incomplete rectification.

Ground is ground, except when it isn't. Ground in the trunk at the battery is not the same potential as ground in the front of the car at the other end of that negative battery cable. It has a finite resistance and the end result, even if you ground one end to the chassis, is a ground loop.

Attaching a second battery, assumed to be in parallel, can create another ground loop depending on how you ground it. The alternator that is charging both of them is in the front of the vehicle. So you're going to have a 12 volt DC signal with a small AC component running to your batteries. Anything you feed off the batteries and therefore the alternator will have that ripple in the power. Also, the grounds can pick up the ripple from power cables running too close to the ground wires, especially if the power wires are not well shielded. Then you have a ripple voltage running around the grounds which are not all attached in one place, creating ground loops with the ripple induced voltage on it.

I'm no audio expert, but to me the solution involves
1) ensuring the lowest AC ripple out of the alternator you use. Killing it here keeps it from propagating elsewhere.

2) sufficiently shielded cables (power and signal) to keep ground wires from picking up the ripple voltage.

3) single point grounding. All of your grounds should come together at a single point that presumably in this case grounds to an extremely clean connection to the chassis. If you think about splice packs, it's the equivalent arrangement. Space pack spring multiple grounds together physically and then the output is grounded. This guarantees that those ground wires are all at the exact same potential, so there is no driving force for any current to run down one ground leg and up another. I'm sure it is not straightforward to do in car audio, but I think electrically would be the ultimate solution. It may not be practical. I'm not saying it is. But your question sought how to eradicate this.

Also, I do not know what you mean by 1 amp ground. Are you saying the grounding cable can carry up to one amp tto the chassis? It may be a very low resistance path to ground, but it also may not be the lowest resistance path of the ripple to travel between the different branches of the grounds. Electricity travels the path of least resistance, literally.

Also do not understand the title of your post. What does the two amps refer to.

One of my coworkers at the power company installed a very large capacitor to save the alternator on his Mercedes. He had a trunk full of amps and speakers everywhere. Sounded like an old time rock concert from the 70s.

i updated parts of my original post in italics to try and clear things up. tonight i removed the second battery from the equation, and also the amp for the subwoofer. also if you are unaware, the oem battery location is in the trunk on the ion. Removing the second battery and second amp from the equation didn't improve anything. I will try to test the rectifier tomorrow, and try and measure ac ripple. Would running a large ground from the alternator body to some grounding point in the trunk help at all? Here's a pic of the battery frame ground
https://cimg1.ibsrv.net/gimg/www.sat...1a38499546.jpg

Those ginormous capacitors that people use in car audio store additional charge that can be quickly released when there is a sudden large current draw on the system, like very hard bass hits. Something that would dim the headlights if they were on. It would also probably wreck the battery in short order or shorter order..
The issue usually comes down to the alternator feeding ripple on the positive side because it is either defective in the rectification stage, has ripple riding on the ground, or is not sufficiently grounded to a vehicle ground. Below is a part of an article I stumbled across after reading your last response. Hope this helps.

https://cimg1.ibsrv.net/gimg/www.sat...8a48dbd3a3.png
It also mentions getting noise filters and adding them in certain places to squash the unwanted voltage and current noise from running around in your system

it was the remote turn on wire causing problems.

edit: issue is back

i did the diode test on the multimeter, and the reading didnt change from 1 when flipping the leads around, with one on the case of alternator. changing the one side from alt case to a point on the block near the oil filter housing resulted in a value around 600 ( or 500 i dont remember exactly). I'm assuming this is the original alternator. i have seen 14v at the battery with car on.

I would have the alternator checked with the proper test equipment.

Ditto on what Andy said. That's really close to the top range you want to see from an alternator as far as I remember. Which ain't too far.

what do you mean by tested w/ proper test equipment. to access the alternator to probe, i had to remove the intake tube from the airbox to the manifold, so i was unable to do any testing with the car running because it wouldnt stay running with the MAF disconnected. also fwiw, i recently moved the head unit ground to all the way to the battery.