What does a capacitor do?
Stiffening Caps
What are they? What do they do, really?
This definition will be in its simplest form. You will see audio capacitors referred to as Stiffening Capacitors. A capacitor is a devise that stores electrical energy. Well, you say that’s what a battery does. Well yes it does, but the difference is the ability and speed that this electrical energy is able to be discharged.
Batteries are designed to store electrical energy for long periods of time. A battery also discharges slowly. A capacitor charges and discharges very rapidly. The reason behind this is due to the internal resistance of both devices. A battery has a high resistance that allows for long-term energy storage and a slow discharge. The capacitor has virtually no internal resistance, which allows for rapid charges and discharges.
An amplifier requires current as music signal passes through it. This creates transient signals in the amplifier. The problem occurs when many of these signal come in rapid succession in a short period of time. The time we are talking about are very small fractions of a second (milliseconds). If your electrical system is unable to react to this it causes a sagging effect in the audio output.
As the current goes up, so must the voltage. Since you can’t increase the voltage as the current requirement increases we get a decrease in voltage and this decrease in voltage causes a sagging power supply. Amplifiers work best at 14.5 volts and can easily overcome a factory installed alternator current output capacity. When the engine is turned off, the system requirements are supplied by the battery increasing the problem of supplying the transient requirements. You could add 10 or 20 more batteries and it wouldn’t help. Remember, as we explained above batteries can’t supply energy quickly enough to supply the transient needs of the amplifier. Please note that these transients may be 100 amps. They occur so fast that your fuse will not be effected, remember this takes place in milliseconds.
By adding a large stiffening capacitor to your amplifier input power line you should be able to meet these transient requirements. Remember as we explained above, a capacitor can store energy very fast and discharge energy very fast. This should solve the transient current requirement to the amplifier.
The voltage of the capacitor can only be the same as the alternator output or if the engine is off, to the level of the battery. So, as you can see a capacitor doesn’t maintain battery levels. If you are still having energy shortages to operate your system you may need to look into a high output alternator.
Thanks to Grimor for the article
