12 volts X 4 amps = 36 watts. Actual voltage will be more like 14 with the engine running, so 3 amps of current draw at 14 volts would produce 42 watts. Each halogen bulb would draw somewhere between 3 and 4 AMPS to produce its rated wattage. I run a pair of 55 watt halogen driving lights on my Honda Gold Wing, and the original equipment charging system keeps the battery up with no problem. I have no idea what amperage capacity that one is. WATTS = VOLTS X AMPS. A 55-65 amp alternator will produce all the current the average electrical system will ever need unless a 4 jillion watt sound system and/or a bunch of lowrider electro-hydraulic pumps are being powered.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!