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"How Do You Know if You Need a Power Capacitor?

The first way most people know if their system is in trouble is headlights dimming. To most car audio enthusiasts with a passing knowledge of electrical systems this means a capacitor is needed. Headlights dimming? Get a cap. And that's a pretty good guess but not always true and certainly not a guaranteed cure. A power capacitor can only do so much. If your electrical system only has a scrape it's a good band-aid but if it's really bleeding you need stitches. And stitches come in the form of an upgraded alternator and battery. If the headlight dimming only occurs at idle then it probably isn't much to worry about and a power capacitor may help. An idling vehicle puts out much less current from the alternator while the current draw from the audio system remains the same.

What Size Car Audio Power Capacitor Do You Need?

Since the beginning of car audio power capacitor time (late 1980's) the accepted rule has been one Farad of capacitance per 1,000 watts of power with a minimum of one Farad (that last part is often forgotten). This value was determined experimentally by Richard Clark (of Autosound 2000 and Buick Grand National fame). More isn't necessarily better but it doesn't hurt either."