audioholic
5,000+ posts
not a moderator
First off, I want to remind you guys that this is the tech section, insulting other members is not allowed here. Id delete the insulting posts, but that would be like 2/3 of the thread. I'll just ask that you guys tone it down. Remember, we are all here because we enjoy the same hobby, lets not treat each other like enemies just because we disagree on any particular subject.
Secondly, caps *can* help a charging system in a car, but not like most people think. The bad rep caps have gotten is due to manufacturers and retailers trying to fool us into believing a cap is generic fix for an insufficient charging system. This is incorrect.
There is a lot of talk in this thread about system voltage. Caps will not help long-term system voltage problems. And by long term, I mean any voltage dips that last for more than a second or two (usually less).
A cap is ultimately a storage device that follows system voltage. If system voltage drops, the cap discharges until it equalizes with the system voltage. When system voltage goes back up, the cap's voltage does too. Which is a slightly more complicated way of saying it recharges only once the charging system 'catches up' and voltage begins to rise. So the old wives tale that a cap is 'trying to recharge' just when the system needs power the most (bass notes) is not really true. Its just sitting there waiting for system voltage to go back up so it can follow it and recharge.
A cap's low internal resistance allows it to discharge rapidly. Its design (electrolytic types) limit's its storage capacity to relatively very small compared to a standard battery. So when system voltage drops, it discharges by equalizing with system voltage, very quickly. So those long bass notes, the cap has shot its wad at the beginning of, and once system voltage inevitably drops anyway, the cap pretty much does nothing. Only once the charging system recovers, usually by the bass note ending, does the cap recharge and gain that potential energy it will discharge once its needed again. So any long term voltage drops your system produces, will not be helped almost at all by a cap.
What caps DO help is to provide a low resistance power supply (albeit a small one) very close to your power draw. Music is transient, its spikes and dips in current draw on the charging system can be very rapid. In systems where wire resistance or other resistances found in the power supply circuit is excessive, a cap can be beneficial. But the potential value of this is acoustically (the bass will react quicker), not one based on sustaining charging system voltage levels. And if your ears are capable of hearing the subtle nuances between that system with or without a cap is debatable. Also worth noting is that amplifier manufacturers already place an array of small caps in the input stage of their amplifiers, so the need for more capacitance is also debatable.
ESR. Electric series resistance. Once you understand what I said above, what a cap *can* and *cant* do to help your system, you are ready to understand why ESR is important. Simply put, the higher the ESR, the slower it reacts. And we want a cap for fast reaction to transient power demands, right? Also, once a cap equalizes with system voltage, it DOES create a power drain in the form of that internal resistance. So while I said above that a cap does not 'try to recharge' when system voltage is still low from that long bass note (the old wives tale), it is true that at that low point in system voltage the cap has no benefit to the stereo/charging system, but its resistance still affects the circuit. It maintains that resistance based on ESR whether it has equalized with system voltage at 14.4, or at 11v. This is the kernel of truth, that a cap does present a draw on a charging system even when voltage is low, that spawned the old wives tale that a cap will make your charging system 'work harder' because it is 'trying to recharge'. That subtle difference in how a cap recharges, has spawned this whole capacitor craze and the backlash of it, that almost always dictates these online arguments over its relevance to your car audio system.
It is true that smaller caps present a lower ESR. This is why is best to wire an array of smaller caps together, rather than buying one single large cap. Four .25 farad caps wired together would present a smaller resistance than a single 1-farad cap would, all other factors being equal.
Long story short, caps are not meant to prop up an insufficient charging system. They do have potential benefit to a car audio system, but the benefit is small enough to usually not warrant the purchase. And yes, in the case of those large caps with multi-tens of farads, they are generally worthless.
Secondly, caps *can* help a charging system in a car, but not like most people think. The bad rep caps have gotten is due to manufacturers and retailers trying to fool us into believing a cap is generic fix for an insufficient charging system. This is incorrect.
There is a lot of talk in this thread about system voltage. Caps will not help long-term system voltage problems. And by long term, I mean any voltage dips that last for more than a second or two (usually less).
A cap is ultimately a storage device that follows system voltage. If system voltage drops, the cap discharges until it equalizes with the system voltage. When system voltage goes back up, the cap's voltage does too. Which is a slightly more complicated way of saying it recharges only once the charging system 'catches up' and voltage begins to rise. So the old wives tale that a cap is 'trying to recharge' just when the system needs power the most (bass notes) is not really true. Its just sitting there waiting for system voltage to go back up so it can follow it and recharge.
A cap's low internal resistance allows it to discharge rapidly. Its design (electrolytic types) limit's its storage capacity to relatively very small compared to a standard battery. So when system voltage drops, it discharges by equalizing with system voltage, very quickly. So those long bass notes, the cap has shot its wad at the beginning of, and once system voltage inevitably drops anyway, the cap pretty much does nothing. Only once the charging system recovers, usually by the bass note ending, does the cap recharge and gain that potential energy it will discharge once its needed again. So any long term voltage drops your system produces, will not be helped almost at all by a cap.
What caps DO help is to provide a low resistance power supply (albeit a small one) very close to your power draw. Music is transient, its spikes and dips in current draw on the charging system can be very rapid. In systems where wire resistance or other resistances found in the power supply circuit is excessive, a cap can be beneficial. But the potential value of this is acoustically (the bass will react quicker), not one based on sustaining charging system voltage levels. And if your ears are capable of hearing the subtle nuances between that system with or without a cap is debatable. Also worth noting is that amplifier manufacturers already place an array of small caps in the input stage of their amplifiers, so the need for more capacitance is also debatable.
ESR. Electric series resistance. Once you understand what I said above, what a cap *can* and *cant* do to help your system, you are ready to understand why ESR is important. Simply put, the higher the ESR, the slower it reacts. And we want a cap for fast reaction to transient power demands, right? Also, once a cap equalizes with system voltage, it DOES create a power drain in the form of that internal resistance. So while I said above that a cap does not 'try to recharge' when system voltage is still low from that long bass note (the old wives tale), it is true that at that low point in system voltage the cap has no benefit to the stereo/charging system, but its resistance still affects the circuit. It maintains that resistance based on ESR whether it has equalized with system voltage at 14.4, or at 11v. This is the kernel of truth, that a cap does present a draw on a charging system even when voltage is low, that spawned the old wives tale that a cap will make your charging system 'work harder' because it is 'trying to recharge'. That subtle difference in how a cap recharges, has spawned this whole capacitor craze and the backlash of it, that almost always dictates these online arguments over its relevance to your car audio system.
It is true that smaller caps present a lower ESR. This is why is best to wire an array of smaller caps together, rather than buying one single large cap. Four .25 farad caps wired together would present a smaller resistance than a single 1-farad cap would, all other factors being equal.
Long story short, caps are not meant to prop up an insufficient charging system. They do have potential benefit to a car audio system, but the benefit is small enough to usually not warrant the purchase. And yes, in the case of those large caps with multi-tens of farads, they are generally worthless.
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