Alternating current (1 - 1.5 A) in alternator output

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!

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

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?

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

-Rod

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