alternator size?

How can I calculate/find out what size alternator I need?  I will have 800watts rms.  is the stock 75amp alternator enough? I do not plan on adding any more amps or power. thanks

RF 500a2=500rms

RF 600a4=300rms

you will draw 58.39916 amps. with only a 75 amp alt thats not much left over for your a/c, lights, and any other acc. you might have. thats only 16 amps. and that 75amps is a cold reading when it gets hot you'll lose 5 or 10 amps. I would upgrade to a 100 amp or more alt you will be glad you did.

Just because your fuses are rated at x # of amps does not mean that your amplifiers draw this much power all of the time or even most of the time. Current draw will depend on a number of factors such as effiency of your amplifiers, the output voltage of your cd (allows gains to be turned down), the type of speaker you are using (tweeters cause an amp to draw lots of current, subs do), the type of music you are playing, how loud you want to play your music, how long you expect to play your music, how loud and long you expect to play your music. I'll bet that your not the conservative snot nosed elevator music type, but if you were you could probably play that music at a moderate volume level all day long and have no alternator issues, if you are a hard core bass junkie that has to wake up the city and keep them awake all night, then yes an alternator is in your future.

I would take a wait and see approach, I would upgrade all of my wiring properly, ensure that I have a good battery, a stiffening capacitor and make sure my system is running at peak efficiency. If you find that the voltage is still dropping like a rock or your headlights or dashlights are flickering worse than ever, consider then an alternator, second battery + isolator. Take it a step at a time, dont's spend $ if you don't have to.

a second batt and cap will do no good with out a alt to power them. get the alt. I'm 38 years old and i have been doing this stuff for over 23 years. get a 140 amp alt. trust me it's worth it.