How do you figure out the amount of amp your altinator need to put out to run a multi amp car audio system

Your amp will have a peak and steady wattage specification. Then the formula is Amps = Power/14. You can make an estimate of peak and steady amps from that. It is worth noting that at a lowish voltage like 12V, high power produces high currents.

The job of the alternator is to charge up the battery, which you would know. Once the battery is charged up fully the alternator is effectively disconnected by the regulator. So to prevent the battery from running down in use the alternator needs to supply enough current to your audio amps, plus enough to run the car as well.

A typical alternator in a medium size car can produce about 14V and 50-70A, This is regulated to about 10A at 14V. So if your audio amps pull about 5A they would be developing about 5 x 14 = 70 watts steady. Peak power spikes can be buffered by the battery. Most car audio systems are nowhere near this powerful.

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