battery getting drained while driving

belt system is March performance,so really cant change the pulley size,The belt tension is manual not idler.When the car is at reg. idling speed the alternator seems to stop charging. when I kick up the idle speed the alternator starts charging,but the charging rate is vary slow.I had heard that one wire alternators turn off at slow idle and kick back in when rpm pick back up,but did not think would pick up so slow.Is this normal?