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Following this need to learn more

XS Power D5100, 2 D2700s, & 2 D975s

MechMan 220a Alt


Kicker 650.4

2 12 Ascendant Audio Mayhem's

Pioneer DEH-P7200HD

Rockford Fosgate 3sity.1

Build log: http://www.stevemeadedesigns.com/board/topic/166792-88-nissan-maxima-trunk-build/#entry2430899


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Can you prove that?

I can prove that dollar for dollar there is something more effective than a cap for daily use, but not that the capacitor itself is detrimental :unknw:

I'm all ears . . .

XS Power D1200 - 44Ah $216.99

Rockford Fosgate RFC10HB - 10 farad, $229.99

1 farad is 1 amp second


44Ah x 60mins/1hour x 60seconds/1min = 158400 amp seconds - equivalent to 15840 of the Rockford capacitors for 13 dollars less.

And lets say that you exceed your alternator's power output at a certain frequency - say for 3 seconds in a song, and you exceed it by 20 amps The capacitor would be discharged in a half second, making it not only useless for supplying power, but also an additional drain on the alternator as it charges back up. While the battery can supply that power and although it will take some power to charge itself back up, it still has some "reserve" power left over to aid in keeping the voltage steady while the capacitor just fell flat on it's face, per-se.

From Wikipedia - A farad is the charge in coulombs which a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second.

Did you know wikipedia is a source all colleges frown on as a reliable source due to the fact anyone (including my uneducated ass when it comes to EE) can post information as 'correct' information? :P

Now on with the lesson kind sir.

(I know, I know...Snafu is a guru posting wiki, so it must be right hence the smiley)

Did you know that there is a phenomenon among groups of people that make it so that the average answers among that group are more often the correct answers?

This is often seen in games shows like "Who wants to be a millionaire" when the audience is invited to give a suggestion. Most often, the majority answers are correct.

Wikipedia operates from this principal. Sure, any one of 100,000 people can add info to an article, but then there are 99,999 more to check their work.

Damn it Ed..lol I didn't expect you to fall for it. I know the accuracy is high, I was just giving Snafu crap.


We actually had a discussion in a class about the use of wiki. Most Professors agree it is accurate up to 99%, but it is that 1% being the reason it is not allowed..unfortunately. Granted, I still used them and then used the references they listed lol.

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From what I have read of you posted, what we did was the correct thing to do, it was no more then a volt meter and causing more issues then it helped.


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Caps don't hold enough power to be useful - even nice ones will be drained in a fraction of a second

My DC5K has 24 1200uF caps in its power supply input which are used to produce >5kW.

That adds to 28,800uF.

Most basic stiffening caps are 1F = 1,000,000uF.

Still think they're "small"?

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Caps don't hold enough power to be useful - even nice ones will be drained in a fraction of a second

My DC5K has 24 1200uF caps in its power supply input which are used to produce >5kW.

That adds to 28,800uF.

Most basic stiffening caps are 1F = 1,000,000uF.

Still think they're "small"?

yes... still small.. the capacitors in that 5k's power supply section are not there to be the supply of power.. see snafu's post from before on how capacitors are used for many different purposes in electronics, from conditioning, to filtering, etc.

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5 farad

i found the problem


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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.

I have the same cap and have had similar results with the cap helping with voltage drop.
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I should be studying for finals, but i am reading the article and doing research on caps. Damn you snafu

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J=CV^2 (J= joules, C=capacitance, V=voltage)

for a 1 farad capacitor on a system charging at 14.2 (voltage = random number somewhere around normal car voltage I pulled out my ass for the sake of this post)

J = 1 x (14.2x14.2)

J = 201.64

ok lets round that to 200

ok so 1 joule = 1 watt for 1 second.

now lets play with those numbers.

we all know amplifiers aren't perfect, power is lost to heat, etc. a pretty common number to see is 70% efficiency at 1 ohm on a class D amp.

lets say you're the typical sort of SMD person. you want bass. you want it in your face, you like the long drawn out demo music, low notes, etc.. you stive for a big, powerful system.

so lets start the number game at 5000 watts, at 70% efficiency, that amp needs 7142 watts of input.

and remember from before, 1 farad = roughly 200 joules = 200 watts at 1 second.

7142 / 200 = 35.71 . round it up to keep from getting bogged down. 36

so that's 36 joules if the amp is operated for 1 second.

lets keep playing with the numbers cause 36 farads is a ridiculous number for 1 second of play.

say you put a nice single 275 amp alt under the hood, that charges at the 14.2 as we started this whole thing out at.

wattage = voltage x amperage

275 x 14.2 = 3905 watts from the alternator

bare minimum to run the car itself is say.. 60 amps or (60x14.2=852) call it 900 watts for overhead.

so we got.. call it 3000 watts left for the system

7142 - 3000 = 4142 watts still needed for the system

4142 watts @ 1 second = 4142 joules / 200 = 20.71 call it 21 farads needed.. per second

still haven't taken batteries into the equation here but we'll leave them out of this for now.

ok so 21 farads per second, for 30 seconds of a bass race 630 farads.

So who's buying me a 630 farad capacitor bank?

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i have a cap in my setup, its a 4 fared going to my kicker 1k monoblock. my ear-o-meter can detect that its just alittle bit more precise and when it would normally crap out, like when theres just alot of bass changing notes alot, it pulls it out from the bog and makes it more easy on the ears and clear sounding. i love mine but its not really necessary. my electrical system stock on my runner never had a problem with dimming lights at full tilt, well done toyota.

New setup 8-9-13

headunit: kenwood excelon kdc x497

mids/highs: alpine type s 6.5 comps front/5.25 coax rear

substage: 2 PSI pf1 high performace upgraded 15's

mids/high amp: alpine mrx-f65

substage amp: DC audio 2k

optima (for the time) red top in back

skyhigh 0ga wires (minus sub amp, which is some borrowed 0ga, lol)

build log soon

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