Alternator whine.

[Bycrick]

Measuring alternator whine. First, most inexpensive AC voltmeters don’t actually indicate the correct voltage unless the AC is a good sine wave. So to measure the ripple, you’ll need a meter which read True RMS. Second, based on the several articles I found, there doesn’t seem to be a good agreement on how much ripple is "too much."

So I’d probably try to find somebody that had the good AC meter. They’re much more common than an o-scope. If you read a few hundred millivolts of ripple, you’re probably OK. If it’s several volts, then you can take the alternator apart to check the diodes.

When you install a new alternator, measure the ripple right then. It gives you a baseline for detecting future problems.

[Compass790]

Originally Posted by Bycrick

Measuring alternator whine. First, most inexpensive AC voltmeters don’t actually indicate the correct voltage unless the AC is a good sine wave. So to measure the ripple, you’ll need a meter which read True RMS. Second, based on the several articles I found, there doesn’t seem to be a good agreement on how much ripple is "too much."

So I’d probably try to find somebody that had the good AC meter. They’re much more common than an o-scope. If you read a few hundred millivolts of ripple, you’re probably OK. If it’s several volts, then you can take the alternator apart to check the diodes.

When you install a new alternator, measure the ripple right then. It gives you a baseline for detecting future problems.

Ok thanks for that.