capacitors...yes or no...

[IgnoreMe 5,000+ posts]

after being in the car audio scene for a while, ive come to the decision that caps in fact do not work for long dragged on bass notes. however do work nicely for rock or songs that the bass notes are not so drawn out. then i came to the decison that caps are not worth the money and are a load on the system. however, i came across this thread at termpro

http://audioforum.termpro.com/topic/6/975.html

it argues that opposite of what i thought. anyone else care to chime in? ive heard so much shit about capacitors this way and that way that even after years of messin around with car audio and always reading about it, that im STILL unsure of whether or not i should buy a capacitor.

"No, the cap can store a small amount of energy and disperse it extremely fast - the larger the cap, the more it can store, many factors effect have fast it can discharge it.

However, Let's say that you have 200 amps of current capacity at 13 volts from the alternator after all of the vehicle electronics are satisfied. The capacitor can only charge/discharge from the current that is available to it and is only useful when the amplifiers draw enough current to drop the voltage below what the cap is charged at. Then it will only discharge the cap to the level that the system voltage drops to. Then it will re-charge at the rate the alternator can deliver it, but it is always faster then the amplifier can use it.

Any way that you slice it, the current producing devices are the limiting factor. The cap is just a fast battery, but its so fast that the load (the amplifiers) can't keep up with them. A capacitor is never a drain on the system, I don't care what some people have come to believe. Absolute worst case scenario in falling voltage with a heavy constant load then the capacitor will just float at the system voltage level. They are not parasitic devices, they are limited storage devices and people that tell you otherwise simply don't understand the physics behind their operation. The absolute WORST thing that they can do is nothing. I'd be a lot more concerned with voltage drop from the multiple terminals and connections when installing caps then I would be about them being a load." by Chris Dilbeck on page two of the thread. this one in particular caught me off guard. discuss....

edit: see the bolded part? so now im assuming even while playing a frequency the capacitor can still charge up? i always thought once the cap is discharged it stays there until there is NO load and it can charge back up?

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[jdawg 5,000+ posts]

I dont really see anything there that hasnt been said here. Caps have their place. To help a weak underpowered electrical system, no. Fix your electrical system. Larger alternator, redo underhood wiring, better or more batteries. If this is already done and you still have some light dimming, then yes add some caps.

 

[helotaxi 5,000+ posts]

If you really get into the physics of what the cap will do for you, they serve only one purpose: put money on the pocket of those selling them. They can't store enough energy to make a difference except with the largest of caps with the smallest of systems. Each Farad of capacitance gives you a whopping 0.5 amp second of energy reserve assuming that the ESR of the cap would allow full voltage out of it. Since the latter isn't true, the usable capacity is even less. If you think that negligible amount will make a difference not matter how robust your electrical system is, you're fooling yourself. Richard Clark (as much as I dislike the guy and disagree with a lot that he has said) was the first to use external capacitance in a car system. He didn't use them to help with current delivery, he used them to filter the voltage ripple from the alt before it got the amps. They were power conditioners, nothing else.

 

[stratusrt01 10+ year member]

I saved a bunch of threads that Richard Clark wrote on the capacitor's use in car audio and compiled them into a thread. If you've got the time, it's a good read, and really explains it well, with examples and numbers:

http://www.forum.realmofexcursion.com/showthread.php?t=17970

 

[IgnoreMe 5,000+ posts]

If you really get into the physics of what the cap will do for you, they serve only one purpose: put money on the pocket of those selling them. They can't store enough energy to make a difference except with the largest of caps with the smallest of systems. Each Farad of capacitance gives you a whopping 0.5 amp second of energy reserve assuming that the ESR of the cap would allow full voltage out of it. Since the latter isn't true, the usable capacity is even less. If you think that negligible amount will make a difference not matter how robust your electrical system is, you're fooling yourself. Richard Clark (as much as I dislike the guy and disagree with a lot that he has said) was the first to use external capacitance in a car system. He didn't use them to help with current delivery, he used them to filter the voltage ripple from the alt before it got the amps. They were power conditioners, nothing else.

ok that makes sense. see ive heard people say that they will put out 100 amps for .01 of a second. lots of misinformation out there. but i did some price checking and the decent rockford 25 farad caps...are like 350 bucks...i think i would much rather put that into a dual alt setup instead. anyways, i got another question. ive also read that alternators are slow reaction. meaning the bass hits, you dim, and THEN the alternaor will make the power that is needed to keep voltage where it needs to be. so am i correct in assuming that i could use, say a 1 farad cap to keep that initial dim from happening before the alternator has a chance to start making power...or is this just something stupid i read on line as well?

 

[n2audio 5,000+ posts]

ok that makes sense. see ive heard people say that they will put out 100 amps for .01 of a second. lots of misinformation out there.
...am i correct in assuming that i could use, say a 1 farad cap to keep that initial dim from happening before the alternator has a chance to start making power...or is this just something stupid i read on line as well?

Put the cap near the headlights if dimming is the issue.

ive heard people say that they will put out 100 amps for .01 of a second. lots of misinformation out there.

well, .5A for a second would be 50A for .01, so it doesn't agree with Helotaxi's approximation - at least it's in the same order of magnitude.

 

[helotaxi 5,000+ posts]

100A for .01 sec is 1 amp second. Problem is that the cap's ESR will keep that from being the case.

 

[LOUD 4DOOR 10+ year member]

Whats up with the ghey thread started here

 

[lil azn 06 10+ year member]

What if i was to put a cap for the electrical system of my car? Such as before the battery to the main fuse for the car? Instead of helping only dimming headlights, it could also help with the entire lighting system of the car. Or does the cap still not provide enough power reserve for even that?

 

[audioholic 5,000+ posts]

Let me add another wrinkle... there are capacitors in your amplifiers' input stages.