if the current charging system cant keep up with the draw - causing dimming lights, why would adding an additional device be healthy for the system? An alternator can only handle so much. you start throwing more caps and batteries in there to try and "fix" the problem, you are just causing premature failure to the alternator. A cap should be the absolute LAST item to add/upgrade in the electrical system. Only when you know that the rest of the charging system is healthy enough to handle all of the additional devices.

 

Essentially the battery is a cap (well sorta) but thats kinda what i was thinking, if your alt. cant handle the total power being taken by the system then a cap. wouldn't help, unless you could make it so the cap didnt have constant power being put in and taken out (like a battery does) and constantly be charged then only be used for short high power bursts that would cause the lights to dim then that would be useful so i can see where Trucktom is coming from. but thats basically saying that your alt will handle just about everything, but your system might at some times pull just a little more power than the alt will handle which is where the cap comes in. But then the proper way to fix that would be a better alt.

Im not sure if what i said makes any sense to anyone but that's kind of a dumbed down version of how i see it.

 

Actually, no.

We're not going to get into a physics lesson but caps store electrons directly and can respond instantaneously, in terms of powering audio. Batteries store a charge and feed it back out by chemical process. There is what's called a surface charge which acts like a cap but it's relatively small. The chemical process can start in milliseconds but that's also the frequencies where you need power fast.

The bottom line here is you want to match your power source to your system. I get the impression you're not really building a rattler but using enough amp power to make sure you can get concert level sound without distortion, right? IOW clean sound more than bone rattling.

Now you have to balance that with the stats on how much current your amp draws in a a quiescent state, power on/ no sound; vs how much it can deliver to the subs at peak. The higher the fidelity, the lesser the ratio.
That where the bias of the final drivers comes in. Yours is probably class AB, which is fairly efficient .. only a little power through the speakers until there's work to do. Class A on the other hand, sucks power because it sorta treats the voice coil like a stepper motor {not accurate but an analogy for current always on}

I'd go with a 140 A alternator

 

yeah i took and am taking physics, i know what a cap does i was just trying to think of how it could be used here.

 

I never ran them before with my 2400 watt amps, and my alternator never gave me problems at all. It would be a good thing to have to help with the system, but you don't really need it for that little bit of power.

 

The only thing caps are good for is filtering out noise off of the DC supply, noise that can be caused by the alternator and other misc thing in a vehicle. Using them to boost a system is not real effective. Extra battery, bigger alternator and Big 3 are much better upgrades to deal with heavy current draw objects like an amplifier.

 

Yes and no. If you really understood the video you yourself posted in the other thread, you see they are one and the same.
The difference is magnitude and ability/capacity to respond to fluctuations. In other words source impedance.
If I were interested -rather than wanting to pull some guy out of his thumper and smashing his face in with a brick when he pulls up next to me at a light - I would get the bigger alt, do the big three, get a hi-cap low impedance battery and build a Power buss from the battery to the amp from copper tubing inside copper tubing inside PEX water tubing.
But I'd still have some caps for 'filtering' out the pops and sags.
Whatever.

 

I think you misunderstood what I was meaning by it. If he was just concerned with controlling the dimming of the lights and such, there are better upgrades than a cap to take care of that.

For a good system, caps are necessary, but then again not everyone is interested in a good system so much as making as much noise as possible.

I do understand the video that I posted, probably has something to do with the electrical engineering degree that I have.

I simply gave the short and sweet version of caps are not as effective for controlling what he seemed to be most concerned about controlling.

I never said caps shouldn't be used, simply stated what their best uses are for, which is filtering out noise.

In my world, pops, sags, spikes etc on a DC line is noise.

 

I think everyone has valid points, the problem as I understand it and as pettyfog touched on, it all has to do with speed, capacity, and time.

A capacitor, even 100 farads worth, only holds a small charge in comparison to a battery. They can help with voltage drops, but a person has to remember that drop has to momentary or else it too becomes a load on the charging system as well, not much of one but it does. Where capacitors don't help is in a situation where a person has a vehicle with a small alternator and is trying to pull an additional 200 amps from the factory charging system which is generally sized to be at about 75% its rated capacity just to run all the factory electronics in the vehicle such as the computer, lights, AC, blower, etc. When the bass hits the voltage will drop and a capacitor will help stiffen or hold that voltage up there for a few milliseconds longer. That may be okay for a single drum beat but does nothing for a long bass line. Now, if that drum beat comes over and over again that cap won't do much to help there either. Say the electrical system started with a 14.4v standing voltage and dropped to 13v on the first beat. It will take a few milliseconds for the alternator to respond and most likely a tenth or two of a second for the voltage to come back up, but it won't get all the way back to 14.4v, maybe 13.8 before the next beat hits and pulls the voltage down below 13v to 12.7, the standing voltage of the battery itself if its a good new battery. Now the alt has to charge the battery a tad, run the rest of the electronics, charge the caps in the amp(s) and the big cap. When the drum beats again the voltage will fall a tad farther, not recharge quite as high again and discharge farther yet again on the next beat. As this continues the voltage continues to drop and dimming and heat get worse and worse because there isn't enough capacity in the system to charge it back up. A capacitor simply cannot help an already struggling electrical system keep from dimming and causing heat, at least not in the long run. It can help with dynamic peaks and peak draws, but if the supply isn't there to bring the charge right back up almost as fast as it was used then the capacitor's effectiveness is reduced.

They have their uses, and given enough Farads are on tap can help keep voltage up on some serious draws, but they're not an answer to a lacking charging system. Stout current paths, an alternator with good spare capacity and good low ESR battery(s) are a necessity for any high powered audio system. A capacitor won't hurt anything at all, and can definitely help on the fast draws. It's been my experience though that for most 1kw and less daily systems a good BIG 3 job and a good battery cover it fine in most cases and the additional purchase of a cap and/or a high output alternator simply isn't necessary.