Stiffening capacitor

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A stiffening capacitor (aka power cap) is a car audio component designed to provide power during times of peak load. The large capacitor acts as a power reservoir for the audio system.

[edit] Explanation

The power cap, usually 1 or 2 farads, is connected in parallel between the battery and the amplifier. Multiple capacitors can be connected with busbars to reduce resistance and power loss. The capacitors are quite large and are often decorated with graphics or enclosed in an attractive housing, sometimes with readouts to monitor the capacitor's voltage.

It can only hold a small charge, so a single bass hit can empty it completely. It charges back up when there isn't a large power demand. This makes it inappropriate for systems that will require prolonged delivery of power, as the capacitor cannot supply additional power, only store it temporarily.