audioholic
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A battery stores a charge via an electrochemical reaction. A capacitor stores a charge in a more direct way via an opposing charge between two conductors separated by an insulator.
A battery has more storage capacity, but the chemical reaction it uses to charge and discharge takes time. The more direct method of energy storage the cap uses makes its charge/discharge rate faster.
The common sense conclusion is that a capacitor placed in the power supply circuit will improve transient response time of that circuit. But there are many factors at play this simple view does not account for.
One, the guy who designed your amplifier already put stiffening caps in the input circuit. Why does it need more just to function properly?
Two, a capacitor's charge, and ability to positively impact the circuit's performance, is based on system voltage. If your alt/batt is not adequate for prolonged current draws, system voltage will drop in the entire circuit, including the cap's stored voltage. As voltage drops in the cap, its ability to charge/discharge diminishes, as does its positive impact on any further transient current demands. At some voltage level (exactly when depends on the ESR of the cap) the cap becomes nothing more to the circuit than a resistor (again based on ESR). This is why I always recommend getting a cap last, because once you get the other components of the charging system upgraded to adequate points (alt, batt, cables), it usually removes the need for the external cap altogether.
And three, an array of smaller caps paralleled together tends to produce a smaller resistance footprint than does one large cap of the same capacitance.
All three of these factor need to be considered when making an educated decision about buying a cap. Personally, I feel the detriments of a cap out weigh its positives in an adequately build charging system. My ideal charging system is an upgraded alt, cables, and dual batts with one mounted in the trunk near the amp(s). Mounting an batt very near the amp has a benefit many times over looked, a reduction in line-loss. Due to the difference in resistances the two batts display to the amplifier (because one is at the end of a relatively long piece of wire, up under the hood), in heavy current demand situations like heavy bass notes, the amp will tend to pull more power form the close batt than the front one. Power pulled from the close batt will have better transient response due to the lack of line-loss-caused voltage drop a system with no rear mounted batt would suffer from. That difference is power draws between the front and rear batt will stabilize once the bass note subsides and system voltage rebounds, leaving amplifier performance unaffected. Less energy is lost to friction in the wire during those large transient spikes in demand, so the amplifier see's more of the potential energy created/stored in the system, and system voltage maintains a higher level helping to minimize dimming lights and low voltage situations for the car's circuits. Win-win.
Caps aren't an inherently bad thing to a power supply circuit with a reactive load on it. But the ridiculous size of caps today, and their lights and displays and gauges, mean the ESR of most of these caps makes them a pretty poor bang-for-your-buck choice in solving a 'charging problem'. But the line loss point I made about rear mounted batts above also applies to a rear mounted cap, to a lesser degree. So even using a fairly high ESR cap can sometimes show improvement to an over all system voltage problem in the form of relieving a headlight dimming issue.
And this is just scratching the surface of the cap discussion, but Im leaving it with this basic info because Im bored with this typing. //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif
A battery has more storage capacity, but the chemical reaction it uses to charge and discharge takes time. The more direct method of energy storage the cap uses makes its charge/discharge rate faster.
The common sense conclusion is that a capacitor placed in the power supply circuit will improve transient response time of that circuit. But there are many factors at play this simple view does not account for.
One, the guy who designed your amplifier already put stiffening caps in the input circuit. Why does it need more just to function properly?
Two, a capacitor's charge, and ability to positively impact the circuit's performance, is based on system voltage. If your alt/batt is not adequate for prolonged current draws, system voltage will drop in the entire circuit, including the cap's stored voltage. As voltage drops in the cap, its ability to charge/discharge diminishes, as does its positive impact on any further transient current demands. At some voltage level (exactly when depends on the ESR of the cap) the cap becomes nothing more to the circuit than a resistor (again based on ESR). This is why I always recommend getting a cap last, because once you get the other components of the charging system upgraded to adequate points (alt, batt, cables), it usually removes the need for the external cap altogether.
And three, an array of smaller caps paralleled together tends to produce a smaller resistance footprint than does one large cap of the same capacitance.
All three of these factor need to be considered when making an educated decision about buying a cap. Personally, I feel the detriments of a cap out weigh its positives in an adequately build charging system. My ideal charging system is an upgraded alt, cables, and dual batts with one mounted in the trunk near the amp(s). Mounting an batt very near the amp has a benefit many times over looked, a reduction in line-loss. Due to the difference in resistances the two batts display to the amplifier (because one is at the end of a relatively long piece of wire, up under the hood), in heavy current demand situations like heavy bass notes, the amp will tend to pull more power form the close batt than the front one. Power pulled from the close batt will have better transient response due to the lack of line-loss-caused voltage drop a system with no rear mounted batt would suffer from. That difference is power draws between the front and rear batt will stabilize once the bass note subsides and system voltage rebounds, leaving amplifier performance unaffected. Less energy is lost to friction in the wire during those large transient spikes in demand, so the amplifier see's more of the potential energy created/stored in the system, and system voltage maintains a higher level helping to minimize dimming lights and low voltage situations for the car's circuits. Win-win.
Caps aren't an inherently bad thing to a power supply circuit with a reactive load on it. But the ridiculous size of caps today, and their lights and displays and gauges, mean the ESR of most of these caps makes them a pretty poor bang-for-your-buck choice in solving a 'charging problem'. But the line loss point I made about rear mounted batts above also applies to a rear mounted cap, to a lesser degree. So even using a fairly high ESR cap can sometimes show improvement to an over all system voltage problem in the form of relieving a headlight dimming issue.
And this is just scratching the surface of the cap discussion, but Im leaving it with this basic info because Im bored with this typing. //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif
