Capacitors do only one thing and that is for filtering purposes. Current from your alternator is not 'dirty' it is AC converted into DC through rectifying and the voltage stability is governed by your regulator. If you do have fluctuations in your readings, either check your regulator since its function is directly dependent on engine rpm ie. 700rpm still 13.0v, 3500rpm still 13.0v or this could be the direct function of the newer cars which uses ecu controlled alternator to help improve fuel efficiency. Help this explains...
As for Capacitive Discharge Ignition like MSD, Jacob's electronic it is useful for hard to ignite fuels or when the fuel mixture introduced is extremely rich. Your stock energy (joules) released from your stock ignition system would not be able to ignite the mixture, hence the need to fire more energy within a spark to help promote combustion. CDI coils store energy and has multiple discharge per cycle with longer durations (dwell time). Regular ignition 1 spark per cycle, CDI 4-9 sparks per cycle. Pistol action vs machine gun action. Help this again explains the concept.
Article taken from ICE guru :
A capacitor WILL:
-Stiffen voltage rails. If you experience very brief, momentary periods of high current demand that cause the electrical system to falter only at these rare, peak draw times, then a capacitor will supply the additional current needed (when bass hits) to keep your voltage rails stiff, and prevent damage to the car or audio equipment.
-Increase response times for musical accuracy by reducing delay caused by transient response times between current demands from the amplifier, and response to this by the electrical system. In other words, your subs will respond more quickly, because they don't have to wait for the alternator to supply additional current at the moment of demand. Amplifiers have to provide a very dynamic and quick response many times. A capacitor can assist in this if the rest of the charging system is up to par and not overtly taxed.
A capacitor will NOT:
-replace the need for a larger, high-output alternator and/or a deep-cycle battery or batteries.
If your electrical system is inadequate, the ONLY way to fix this, and again I repeat, the ONLY WAY to fix this, is to replace the alternator. This is the SOLE source of electrical current for your car when the motor is running.
When the motor is turned off, the battery then becomes your source of electricity.
When the battery is run down, and when the capacitor(s) is/are depleted, the alternator has to work even harder in order to supply current to the car, the audio system, and also to recharge the capacitor(s) (which deplete very quickly) as well as recharge the car's battery(ies).
So by adding a capacitor to try taking the place of a high-output alternator, you are actually causing more work for your alternator, and causing even more damage to that stock alternator.
-make your system magically sound 10 times better.
Many people believe that a capacitor adds NO real benefit to an audio system, and this is why you never see before and after demonstrations, or factory capacitor company vehicles at competition events. A capacitor does have it's uses, but it is not a magical fix for a lacking electrical system.
A capacitor is an electronic device which consists of two plates (electrically conductive material) separated by an insulator. The capacitor's value (its 'capacitance') is largely determined by the total surface area of the plates and the distance between the plates (determined by the insulator's thickness). A capacitor's value is commonly referred to in microfarads, one millionth of a farad. It is expressed in micro farads because the farad is such a large amount of capacitance that it would be impractical to use in most situations.
Capacitor and DC voltage:
When a DC voltage source is applied to a capacitor there is an initial surge of current, when the voltage across the terminals of the capacitor is equal to the applied voltage, the current flow stops. When the current stops flowing from the power supply to the capacitor, the capacitor is 'charged'. If the DC source is removed from the capacitor, the capacitor will retain a voltage across its terminals (it will remain charged). The capacitor can be discharged by touching the capacitor's external leads together. When using very large capacitors (1/2 farad or more) in your car, the capacitor partially discharges into the amplifier's power supply when the voltage from the alternator or battery starts to fall. Keep in mind that the discharge is only for a fraction of a second. The capacitor can not act like a battery. It only serves to fill in what would otherwise be very small dips in the supply voltage.
ESR is the equivalent series resistance of a capacitor. An ideal capacitor would have only capacitance. As you remember, all conductors have resistance. In a capacitor, there are multiple conductors like the wire leads, the foil and the electrolyte. The resistance of all of the conductors contribute to the capacitor's series resistance. It's essentially the same as having a resistor in series with an ideal capacitor. Capacitors with relatively high ESR will have less ability to pass current from its plates to the external circuit (to the amplifiers in the case of stiffening capacitors in car audio). Low ESR is desirable when using a capacitor as a filter.
ESL is the equivalent series inductance of a capacitor. Since most electrolytic capacitors are basically a large coil of flat wire, it will have even more inductance than it would have if it were flat. This inductance, along with the small amount of inductance from the wire leads, will make up the ESL of the capacitor. The ESL is essentially the same as having an inductor in series with an ideal capacitor. Low ESL is desirable when using capacitors for filtering purposes.
Even though a capacitor's plates are insulated from each other, there is a small amount of 'leakage' current between its plates. This current is generally insignificant but will cause a capacitor to slowly discharge with no external circuit path between the capacitor's leads.
I hope the above article helps in educating readers and break through the fallacies surrounding capbanks and capacitors in a sound system setup. A capacitor used in ICE setups is not the same as 'Voltage Stabilisers' since the central processor and capacitors used are very different both in form and function. Don't let those two-bit audio shops teach you the wrong stuff. Most of them are chinese businessmen without academic inclinations. Show them this article and I bet they will keep quiet. Enuff said.
By misleading the general populace with half-truths, they hope to lead you into buying more and more equipment and products from them when you claim that your sound system is not 'good' enough or something is not right and needs improvement.
Another time dear foummers