Noticed this recently. System voltage varies 1-1.5V, generally getting worse as the car warms up. At times it’s spiking to 15V, highest I’ve seen is 15.7. This can’t be good.
Car has a few modifications: HID low beams, single high power (360W RMS) subwoofer. Head unit is a Kenwood aftermarket. Other speakers are still OEM originals.
A while after getting the sub, it blew the alternator (which probably was the factory original so I thought nothing of it); got a “good quality” pull from a junkyard (sketchy, it certainly didn’t LOOK in good shape), that blew quickly; pulled an alternator from a you-pull-it, that also blew; finally got a reman from AutoZone and that’s what is in it currently. You can see why I thought these failures were isolated, right?
That was roughly a year ago, so the alternator is still quite new. On inspection, the coils still look quite good. Battery is rock solid, hanging out at 13.3V car off and without load and around 12.3V when playing music in ACC.
Current theory: voltage regulator on alternator is starting to go. I have to question why this happened, especially in light of it going through three alternators.
Related to the sub, probably. Since the coils look fine, it’s probably handling the overall power draw no problem, sub and all. But…
I suspect the secondary issue here is, the amplifier for the subwoofer presents an uneven load, requiring the voltage regulator to switch far more frequently than it normally would need to, causing a lot of strain. The battery doesn’t smooth this out, because it doesn’t start delivering current until its operating voltage, which is 13.5V at the most, significantly below system operating voltage. If true, a suitable capacitor in parallel with the amp should smooth the power draw and prevent future failures. Shouldn’t take much, it’s not exactly a competition system.
I’m no expert though. I’m probably wrong and correct me here.