this is going WAYYYY off topic but i thought i would share.
i built one of those gas powered battery chargers one time for an electric golf cart. i needed more range on the electric golf cart so i had a friend of mine machine an adapter so i could couple a alternator to the lawnmower engine via belt and pulley.
i took off the alternators voltage regulator and hooked up a full wave 3 phase bridged diode so i could get more than 14 volts out of it, because an electric golf car has a 36v battery back and a 14v alternator does no good. sence the alternator now had no voltage regulator, the voltage was dependant on how fast you spun the thing. i used the gas engines built in mechanical rpm govenor to set the rpm's high enough that the alternator put out 42 volts. i used different pulleys to keep the gas engines rpm low enough that i didnt wreck the thing, but high enough to keep it in its power band. because i think i was getting around 20 amps when the alternator was loaded down trying to charge a 36v battery pack. 20 amps isnt enough to move a golf cart by its self, but if i left the engine running while i was inside or doing something else, or working on a piece of equipment then when i got back on the golf cart the batterys were charged enough to keep on going.
the system worked out great, untill the frame rusted and broke in half and i got a new golf cart that has better range.