This calculator will tell you the required alternator rating for your vehicle at peak usage. It may not be possible to meet these specs with a single alternator or even necessary to. Many other factors come into play such as driving and listening styles. It will however give you the ideal answer and a good indication of your present alternator's ability to supply your system.  It takes into account the current draw of the OEM electrical accessories, the current draw from your amplifiers at peak draw and the current draw from any other electrical accessories (neon, fans, strobes...) in your vehicle.

Calculate the Required Alternator Rating for Your Vehicle
Total Amplifier Power? Watts
Amplifier Efficiency? (Class A/B Typically 50-60% Class D 70-80%)  %
Charging System Voltage? Volts
OEM Alternator Rating? (Typically 60-130Amps)   Amps
Total Current Draw of Accessories Added Other then Amplifiers? Amps
Required Current Rating of Alternator at Peak: Amps
Power Drawn From Charging System: Watts
HO Alternators
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