How does a cap recharge on an already strained electrical system?

Question

If a capacitor discharges and regulates the voltage on a low bass note, after the charge is gone (less than 1 second) how does it help an electrical system already strained to the point of dimming the lights? Does it try to suck more power from the already diminished charging system, if so how does this help? Isn't it like borrowing $400 only to pay it back out of your next paycheck and then having to borrow it again?

Just to make it clear, I understand how a cap works. I have installed hundreds of them. I do not understand why everyone thinks they need one if their lights dim. I am looking for someone to convince me that they are necessary because I just don't see it. I have never noticed a change in a customer's car with or without a cap. The lights still dim the same amount they always did.

Answer 1

A capacitor doesn't recharge a system. It acts as a buffer. It takes a relatively low amount of power and stores it until it's needed. It holds enough power for more than just one bass hit. Using a constant small amount of power is less of a strain than a spiking power consumption when a hard bass hits.

Answer 2

The fact that a cap will help the "dimming light" syndrome is a myth. The ONLY cure for this is an alternator upgrade in the end.

A cap is merely there to "filter" the DC supply and add a bit of regulation, but even that can fall short on the wrong setup.

There is a magic spot upon which a cap is useful. That is when the audio system is consuming 1/3 less (but no less than 1/2) what the alternator can produce. This is really the only time a cap is beneficial for the aforementioned.

Quote from KaeZoo, "When Javin pulls out his Richard Clark "caps are useless" forum link, the discussion is about high-farad capacitors (although it's been used out of context to make it look like he's talking about all capacitors)."

Answer 3

First of all, reducing dimming lights isn't really what a capacitor is for. The purpose of a power supply capacitor is to provide a stable voltage supply for an amplifier during musical peaks, thus improving headroom. If it helps with dimming lights, that's a bonus; but if the dimming is what you're trying to fix, you'd be much better off connecting the cap to the headlight wires. (In fact, there are people who've successfully done exactly that, using much smaller capacitors).

The power demands of an audio amplifier are unlike anything else in the vehicle. Most vehicle electrical systems have a relatively steady current draw that only changes when you switch them on or off. The amplifier's current draw when playing music is always changing. On average, the alternator may easily be capable of handling the demand of the audio system, but alternators aren't designed to handle sudden spikes in current draw. The voltage regulator may not be able to adjust quickly enough, or the alternator may just be overloaded very briefly, which leads to a voltage drop. This doesn't necessarily mean you need a new alternator.

The capacitor can store a voltage at nearly the level of the alternator's output. It's not limited to 12.8 volts like a battery. During brief musical peaks the capacitor can provide current for the amplifier. Of course the cap then needs to be recharged, so the load on the alternator isn't reduced--but by that time the musical peak is over and any voltage drop won't have an effect on the sound. During quieter passages, the amplifier can produce music without distortion even if it doesn't have 14.4 volts to work with. Note that we're talking about very short periods of time, here; it doesn't take long to discharge a cap, and it doesn't take long to charge it again, so it's ready to go for the next musical peak (in theory).

The "caps are useless" idea has come about mostly because people have been misinformed about what a capacitor can do.
--They won't help prevent alternator failure.
--They can't store very much charge, so they don't help with longer musical peaks, like sustained bass notes.
--They don't make the bass louder: higher voltage isn't the same as higher gain.
--They don't help if an alternator is just too small, and is continuously overloaded.
--They won't necessarily reduce dimming much, because they still need to be recharged.
--High-farad capacitors typically have a high internal resistance which makes them useless. In general, it's better to have five 1-farad capacitors than one 5-farad capacitor. When Javin pulls out his Richard Clark "caps are useless" forum link, the discussion is about high-farad capacitors (although it's been used out of context to make it look like he's talking about all capacitors).

Anyway, "stiffening" capacitors do have a useful place in car audio; but you have to know what they can do, what they can't do, and in what situations they'll be useful, or you're likely to be disappointed in the result.

Answer 4

By the way, a capacitor has an associated time constant, which basically means that there is a calculated charge time and a discharge time. (noted in time constant) This charging and discharging usually happens at a rate of nanoseconds depending on the time constant circuit. But if your electrical system is strained, the capacitor will only charge to the level of the voltage being supplied. So if your battery is strained and only reading 11.5VDC, the cap will only charge to that amount. (This also has a lot to do with your altenator). Hope this helps...

Answer 5

Kaezoo is right I couldn't say it better.