If I did my research correctly, my '98 Blazer came with a 100A alternator from the factory.

The problem is, when I turn my stereo up pretty high, theres significant voltage drop even though my amp shouldn't be big enough to pull that much current. Even at 3-4krpm theres still a good bit of voltage drop.

100A at 13-14v comes out to 1300-1400w. My amp is a JL 500/1 and after compensating for efficiency it should pull around 750w at the most, which leaves a good ~600w for the rest of the electrical system.

If an alternator is going out do they tend to not put out as much current? The voltage regulation seems to be fine, it compensates all the way up until my amp is turned up, unless the regulation on these Blazers is really lazy and doesn't correct until after the bass note is over.

 

Check it with a Volt Meter. See how many volts the Alt is putting out.

 

yes, definately check it with a DMM.

are you going by the dash gauge? 'cause they've been know to be inaccurate (in any vehicle).

 

The alt is putting 13.8v at idle with minimal load. My DMM is a bit too slow to accurately measure the drop when playing music, Ill burn a cd with sines sometime to measure, but it does indeed drop. Lights dimming shows the drop also.

The "big 3" upgrade has been mentioned to me. I haven't done it yet, but I was hoping my lil old 500w amp wouldnt really call for the big 3. If a vehicle is equipped with a 100A alternator you would think the wiring would be enough to handle it. It's really the only thing I can think of besides some weird alternator losing capacity issue.