Capacitor as a filter?

A capacitor sort of levels out the power, regulating it and making it smoother, much like a power conditioner does for your home equipment.  The batter in your car is constantly changing (wipers, blinkers, brake lights, etc.).  The capacitor is like a battery in that it stores energy.  When the amp hits a loud note and draws power, it will draw it from the cap and not directly from your car's battery, thus keeping the lights from dimming as much and making life easier for your alternator.

Capacitors are said to "oppose a change in voltage" (as opposed to coils or inductors, which are said to oppose a change in current). Another general statement about caps is that they pass high frequencies and block low frequencies. Used as a noise filter, a cap is passing the "highs" (noise) to ground. The lows pass right on by. DC power can be thought of as the ultimate Low Frequency. After all, it is ZERO Hz. You can't go any lower than that! The effective resistance of a capacitor in a circuit is called capacitive reactance. The formula for capacitive reactance is 1 divided by 2 X pi X frequency X capacitance. When a cap is connected from a point in a circuit to ground, it acts as a path to ground which acts differently at various frequencies. By the formula for capacitive reactance, it would be a very high (infinite) resistance to DC voltages, but a low resistance to high frequencies. The higher the frequency, the lower the resistance is. An example: a ONE FARAD cap is used in a circuit. To DC power, it appears as a very high, or infinite resistance. It has no effect on the DC power. But, to a 60 Hz signal, it presents a load of 1 divided by 2 X pi X 60 X 1. That calculates out to be .0027 ohms, which is practcally a dead short! Of course, most caps are of values waaaaaay less than one farad---most are nominally in the range of just a few millionths of one farad (1 microfarad is one millionth of one farad). Ultimately, a cap passes noise (a relatively high frequency when compared to 12 volts DC) to ground when used as a filter cap. Hope that explains it! -tm- Don't wanna hear your "boom-boom," just wanna hear my "weeee-yaaah-deedle-dee."

Don't buy one. You don't need one and the seller is probably just trying to rip you off. I've never seen any real evidence that Capacitors work as intended. In my mind they're a gimmick and an easy way for retailers to sell you a high profit margin item. (Kinda like radio shack making a killing on batteries). New Project: 2003 Pathfinder

Except that batteries DO do what they are supposed to, and DO work as intended... just jabbin', man...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."