I know many engineers here work on cars, so ...
I am debugging my wife's Lexus ES300. The problem is that the OEM alternators (original and replacements) are not charging at idle. At idle speed, the alternator put out 8V to 10V, which is insufficient to charge the battery. At high speed, it does put out 14V. People suggested speeding it up by changing the front pulley (65mm) to a smaller one. I found a 45mm pulley that might work. But would that cause problem at high speed, including burning out the alternator, or worst?