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 dampener for the audio power system.
In high power audio applications the amplifier can require more current than can be supplied by the car battery, because of the battery's discharge characteristics. The slow power delivery can result in poor sound quality, dimming of the car's lights, or other electrical maladies. For audio applications that only require short bursts of power, such as a thumping bass line, it is more economical to install a power cap than to upgrade the car's electrical system.
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 capacitors voltage.
The capacitor charges and discharges rapidly, much faster than a battery could. 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 temporaraly.
A power cap will not help if an audio system requires more power than the vehicles electrical system can deliver. While this usually requires upgrading the car's battery or alternator, a low-cost improvement is to upgrade the "magic three wires." Using thicker wires can increase the current capacity of the system. The three wires are:
- the wire from the battery's negative terminal to the car's chassis (ground).
- the wire from the alternator to the battery's positive terminal.
- the wire from the chassis (ground) to the engine.
These 3 wires are often small and need upgrading. Fixing this common bottleneck is cheap, and is more effective at powering your stereo and preventing the head lights from dimming.