Alternating current (1 - 1.5 A) in alternator output

[Zushi]

Year: 2002
Make: Mazda
Model: Protege5

I've recently been having a look at my charging system, and more specifically my alternator. I've had the alternator tested at a couple places (Autozone & Advanced) and it passed. I will note that for the diode test it said "N/A" and pass on the other two tests. Anyway, I reinstalled the alternator and, using my inductive ammeter, I proceeded to measure the output current of the alternator. At idle I am measuring approx. 12 A (DC) and approx 1-1.5 A (AC). I'm an alternator pro by no means but I do know that the output is rectified from AC to DC. Is there any allowed AC in the output or should there be absolutely none? I also measured voltage between the B+ terminal on the alternator and negative on the battery and I measure 14.15 V (DC) and 0 V (AC)... so there's no AC voltage ripple. Any input is greatly appreciated and I thank everyone in advance for any help!

[shorod]

Since you're not measuring any AC voltage, the AC current you are reading may just be noise rather than current generated by the alternator. You'd really need to use a current probe with an oscilloscope to determine if this is periodic AC or just noise. Does the amount of AC current increase or decrease as you increase the engine speed?

-Rod

[Zushi]

yes, it does increase with the revs. I also measure it at spark plug wires. I actually tested a different car to see what I get and sure enough I measure around 1-1.5 A (AC) off of the B+ terminal on the alternator (Nissan 240SX). I guess its just noise yeh?

[shorod]

Most likely, especially if you're measuring the same amount on the spark plug wires and a second vehicle.

-Rod

[vgames33]

Looks like its noise to me. My meters will pick up AC current from standing under fluorescent lighting sometimes.