under drivepulley low charge

[mopar3.0]

i installed a under drive pulley on my 3,0 last summer, for a few days it worked fine, then the alt died, i installed one that was close to new but looked smaller, not it charges low at idle, but as soon at i touch the gas its all ok?
bad alt or is there a voltage regulaot that could be bad or will i have to live with this because of the under drive pulley?

[DakotaKid]

Because of the pulley.
Alternators need RPM to operate.

[mopar3.0]

i know few people who never had this trouble with their cars,

[D-Cal]

I have the BPE UDP on my 3.0 Shadow. Voltage will drop slightly at idle with the headlights and one other feature on (fan/defroster), stock operating voltage otherwise. It's never caused me a problem. Install a good battery and forget about it, I had somewhat worse symptoms with the tired old battery that came with the car.

[DakotaKid]

To check the condition of the charging system, get a voltmeter and hook it up to the battery while the car is running.