I am making a home made Moped and need to devise a regulator and charging system for the bike. I need to regulate 3-8 volts AC(in) to a steady 7ish Volts DC(out). I intend to use one small incandescent light for my head light and 8 LED tail light setup including running light brake indicator and blinkers.

 

To have a steady 7v dc out from 3-8v ac in, first you need to convert the ac to dc by using a bridge rectifier and then use a buck-boost regulator to keep the voltage at 7v.
Hope I could help.