Alternator A/C voltage question

[80stech]

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.

[Bmwe5320023.0]

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...

[wpoll]

Originally Posted by Bmwe5320023.0

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?