Capacitors - What's the REAL story?

[strangeduck]

Amplifiers already have capacitors in them to account for sudden spikes in current draw.

[mikelbolton]

http://www.glasswolf...ocaplesson.html

Everything you need to know. Documented with real math and real scientific experiments

Thanks, I was looking for his article....

I read a great article on this a few months ago, but I cannot remember where it was.

I'm stealing this from another forum (lemme give credit where it's due: http://www.talkaudio...nd/page__st__40 )

black-cat

Project 2501

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Posted 06 Apr 2004 - 12:26

Week off work, lie in!

Maplin stiffening cap: (same cap as Fusion, Vibe and a few others)

Voltage (v): 14v

Capacity ©: 1F

ESR: 0.0019ohm

Stored energy = 0.5 * C * v^2 = 0.5 * 1 * 12 * 12 = 72 joules.

Max current = v/ESR = 14/0.0019 = 7,368A

Max wattage = 14 * 7368 = 103,152W

Max time it can sustain that for = 72 / 103,152 = 0.0007 second. (0.7 miliseconds!)

Optima Red top battery:

v = 12v

Capacity: 66AH

ESR = 0.0028ohm

Assume 12w load which draws 1A.

66/1 = 66 hours run time

66 * 12 = 792 watt hours

1 watt = 1 joule per second so

792 * 60 * 60 = 2,851,200 joules

Max current = 12 / 0.0028 = 4,285A

Max power = 12 * 4285 = 51420W

Sustain time = 2851200/51420 = 55.5 seconds.

Note these are very much fag packet calculations and do not take into account the drop in voltage during the discharge. For the cap it would extent the discharge from 14v to 0 by about 10x (7ms wow!).

In reality you are interested in only 1v drop, 14v to 13v. A caps discharge curve is exponential so its not 7ms/10, its more like 7ms/100. 70 nanoseconds. (OUCH!)

Batteries have a multiphase discharge, they maintain their voltage for something like 70% of their discharge cycle.

And again if you have no inductive or capacitive elements in the discharging circuit (if you do you have some ODD spanners) then the current is instant. The ESR takes into account the inductive and capacitive elements of the cap/battery.

[alaskanzx5]

i use a 10 farad rockford cap, a 250amp singer alt and i know its not the best choice but an interstate deep cycle battery with (if i remember right) 55ah.

now i was told by several people taking the cap out would help a lot. so what i did was turned the car on and let it rune for about 30minutes with out the headlights heater or stereo on. then i charged each battery on their own. put it all together and went full tilt on my stereo. i was dropping to about 13.1-13.2 volt at and idle. i then took the cap out and fully charged the batteries again and went full tilt with the same song. my voltage drop was down to about 12.5-12.8 but not only that it would suddenly jump back up to about 14.1-14.2 then suddenly drop again where the cap held a constant voltage.

the sound of the stereo wasn't as clean, didn't feel as deep, didn't shake my front windshield wipers and i had a friend with me the whole time who said it just isn't as nice with out the cap. what i learned there is that the cap isn't necessarily providing more more but holding a higher steady voltage. rather then dropping to the mid 12's it was holding in the low 13's. rather then spiking up to the low 14's it held in the low 13's. it gave me deeper/cleaner sounding bass and got the car flexing a good amount more. didn't get on a meter while doing this but i would bet there was a difference in the spl.

i don't see a cap as a power issue fix all but instead as a good stiffener for a good electrical. from my exp it helped regulate my voltage at a higher point then with out it. now i know the battery i used isn't the best for the application but it is/was what was readily available to me that my pocket could handle. with a better battery I'm sure i would have seen a different result but I'm still certain the cap would still help hold a more steady voltage. when i competed this last summer my score was steady though out the day. i dropped .1db after 2 rounds and the last round after letting the car charge for about 30min i went back up that .1db and that was the only time left the car running between runs to charge up.

[HHR Ed]

When I get something setup in a test rig, I will do a test to see how Caps work in certain situation.

I have used and tested them in the past and have came to certain conclusions about Caps.

When first introduced, Caps (at least in the installs I have seen) were installed almost directly on to the amplifier's power supply. The Caps being used were dozens of small caps. The amplifiers of the day usually had output capabilities that exceeded the capabilities of their own power supplies.

The high number of plates on multiple caps gave a large amount of current very rapidly. And because there were so many, they also had a fair amount of capacity.

So they worked in that they increased power and stability of those amplifiers.

This was also what I found when I first started using caps (many small caps) with amplifiers from the late 80s-early 90s.

Flash forward to 2003.

I started testing Caps for my dB Drag car. I used modern large Caps of the day. Monster 1 farads. And used 2 on each MTX 1501D amplifiers. 8 amps total.

I again mounted them with about 3" of wire from the power connectors of the amps.

Electrical was fairly stable, I saw good power of the amplifiers. Was able to consistently hit 155s on a Term Lab.

A few weeks from Finals, I tested with the same electrical which was about 800lbs of batteries and 300A alternator. But this time, I simply bypassed the caps.

Saw more power and started consistently hitting 156s.

Nowadays, I see amplifiers with even more stout power supplies. And I see people using Caps in even more incorrect fashions.

If there is a claim that Caps improve performance, I'd like to see tests proving that.

Can't prove a negative because you can always make excuses.

So I'm all in to see results.

[79Bronco]

Again, I'll post this article...

http://www.glasswolf.net/papers/nocaplesson.html

If you're going to make a post claiming that caps do anything other than hurt a system, please read it first.

Sorry to snake the thread, but it needed to be said before more people posted about something they do not know.

[snafu]

"snake" the thread - not likely . . .

Now, did you realize that the author of that article was also the first person to offer for sale a "stiffening" capacitor intended for car audio use? Back then (1990), people were scared that caps would explode like a bomb in their vehicle if subjected to over-voltage. Richard used to stick one down his pants in trainings and subject it to just that so that folks would rest at ease. I find it interesting that he campaigned so hard on behalf of capacitors, then later reversed his position on them . . .

Stay tuned . . .

[SnowDrifter]

"snake" the thread - not likely . . .

Now, did you realize that the author of that article was also the first person to offer for sale a "stiffening" capacitor intended for car audio use? Back then (1990), people were scared that caps would explode like a bomb in their vehicle if subjected to over-voltage. Richard used to stick one down his pants in trainings and subject it to just that so that folks would rest at ease. I find it interesting that he campaigned so hard on behalf of capacitors, then later reversed his position on them . . .

Stay tuned . . .

I always feel like you take me back to school lol. I love it

Edited December 11, 2012 by SnowDrifter

[alaskanzx5]

"snake" the thread - not likely . . .

Now, did you realize that the author of that article was also the first person to offer for sale a "stiffening" capacitor intended for car audio use? Back then (1990), people were scared that caps would explode like a bomb in their vehicle if subjected to over-voltage. Richard used to stick one down his pants in trainings and subject it to just that so that folks would rest at ease. I find it interesting that he campaigned so hard on behalf of capacitors, then later reversed his position on them . . .

Stay tuned . . .

I always feel like you take me back to school lol. I love it

i think we just about all feel like we are going back to school when he gets on topic like this one.

[Blackedout]

Capacitors are not storage devices. You can prove this yourself. Charge a capacitor. Watch the voltage drop exponentially.

Capacitors only work when the existing electrical system is already next to perfect. Comparing capacitors to water, capacitors wouldn't be able to fix waves (or huge dips in voltage) but they would be able to even out the ripples in the water. (very small voltage fluctuations)

That is all I have.

[snafu]

Wikipedia is awesome . . .

A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in an electric field