The Question has been asked:
How do I get more Alternator Charging power at Idle?

Improving Alternator Output at Idle Speed

There are several ways to get more power at lower engine speeds. If you only require a little more power at lower engine speeds you may be able to use a smaller pulley. The smaller pulley turns the alternator faster at lower speeds thus making more power. When using a smaller pulley care should be taken not to over rev the motor. If you over rev the alternator with a smaller pulley the alternator can fail. I have seen internal and external fans explode and go through the hood of the vehicle with a $10,000 custom paint job.

The best way by far to obtain more power at lower engine speeds is to install an oversize alternator. The physically larger alternators produce more power at lower engine speeds and are much more reliable at higher outputs. Installing a higher output alternator that is the same size as your original alternator will not give you more power at idle unless they use a special rotor stator combination.