Capacitors 101

[ameuba10]

Physically, a capacitor is an electical component consisting of two conducting surfaces separated by a non-conductor (dielectric). In electrical terms, a capacitor is an electrical component that stores electrical charge when voltage is applied. The closer the plates, the stronger the electric field produced. The greater the charge stored on the plates, the stonger the field produced.

This field represents the storage of electric energy. This energy comes from a source and can be returned to a circuit when the source is removed.

Once a capacitor is hooked up to a power supply, the electrons do not travel through the non-conductive dielectric material between the capacitor’s plates. This electrons accumulate on that side of the capacitor creating an excess of electrons resulting in a negative charge. The electrons orbit passes in the through the dielectric and are repelled by the negative polarity of the capacitor.

As these electrons build up creating a negative side to the capacitor, the electrons are more and more attracted to the capacitor’s positive side. Once sufficient charging current has passed to cause the capacitor’s voltage to equal the source voltage, no more current can flow. The capacitor is now fully charged.

Voltage doesn’t pass through this dielectric material but it acts that way due to the movement of electrons on either side. Once a capacitor is charged, it will equal the source voltage. If the source voltage increases/decreases, the capacitor will do so likewise.

The unit of capacitance is the farad. Common capacitors for car stereo installations would be around 1 farad. A farad is the amount of capacitance where a charge of 1 coulomb develops a potential difference of 1 volt across the capacitor plates.

C=Q/V Q=CV V=Q/C
V=Voltage
Q=Coulombs
C=Capacitance in Farads

Coulomb’s Law F=(kQ1XQ2)/(d2)




Before your charge your capacitor, you must discharge the capacitor. To do this, just short out the positive and ground leads very carefully and hold it for a few seconds to be sure that all the stored voltage is released. To properly charge a capacitor, use a resistor between your battery and your capacitor. Use roughly a 1kΩ resistor here. Hook up the resistor to the power wire and let the capacitor charge for roughly 5-25 sec.

[bikinpunk]

lol... I can hear it now...

Thanks for the effort.

Curious why you decided to post this though, when a link to wikipedia would've served just as well.

j/k

[ameuba10]

i knew that you would be the first to post... i just thought that some facts on capacitors would do this site some good. so much arguing on it, we need some facts. i didnt intend this for confrontation, just some information

[bikinpunk]

Originally Posted by ameuba10

i knew that you would be the first to post... i just thought that some facts on capacitors would do this site some good. so much arguing on it, we need some facts. i didnt intend this for confrontation, just some information

Notice that I didn't argue? I hope this thread doesn't turn into that, but knowing how things go with how people always have to give their $.02, it probably will.

I was just razzing you, man.

Thanks for the writeup. Aren't you an EE student?

[ameuba10]

i know that me and you both are mature enough to understand that people have different views and im thankful for that. but yea i am an EE student and this is just some research that i threw together today.

[bikinpunk]

Originally Posted by ameuba10

but yea i am an EE student and this is just some research that i threw together today.

Have you done any studying of electromagnets? I'm actually working on a project for my senior design course (Aero Eng) using these.

[lostdaytomorrow]

All future new guys reading this and thinking about buying a cap. to fix your bad voltage drops (Below 12v while car is running) or dimming headlights (common sign of non-adequate electrical system), keep in mind this will not help, and if it even seems to help (fixing your dimming headlights, which is not probable but stranger things have happened) it is not fixing the problem, but merely masking the problem. Your alternator is still being run full-bore at all times when the amp is drawing more current than the alternator can produce. Think of your car battery as a buffer and the alternator as the actual power source.

Yes, that is a very long sentence. Yes, caps can help with small voltage fluctuations. No, a cap should not be used instead of buying a high output alternator and deep cycle battery(ies).

[ameuba10]

^^never said it would do any of that

[icen]

Sorry to interrupt, but I'm in EE too, this topic is getting me excited !!!
more stuff about capacitor.
The most important role of capacitor in low voltage analog circuits is that it can be used to make high pass and low pass filter and oscillator.
It has an impedance of 1/jwC
(C is the capacitance, w is the freqency in rad/sec, j is the imaginary number)
Knowing the impedance, you can incorporate to any circuits and perform phasor analysis.

About electromagnetism, the component that's related to it is an inductor. It has an impedance of jwL
(w is the frequency in rad/sec, L is the inductance, j is the imaginary number)
Similar to a capacitance, you can also use it in a phasor analysis.

Similarities between inductor and capacitor.
1. They both have complex impedance (strictly speaking, resistance of a resistor is a real impedance)
2. They are both used in analog electronics.
3. They both can be used in signal processing and amplifiers (like LNA and power amplifier)

Differences
1. Capacitor impedance is lagging by 90 degree
2. Inductor impedance is leading by 90 degree


Capacitor and Inductor together?
if you put them together in parallel, they'll become a resonator pool.
The complex part of their impedance will cancel out and they'll have a REAL impedance (resistance). At resonance frequency, their resistance (idealistically) is infinite.

[bikinpunk]

Originally Posted by icen

Sorry to interrupt, but I'm in EE too, this topic is getting me excited !!!
more stuff about capacitor.
The most important role of capacitor in low voltage analog circuits is that it can be used to make high pass and low pass filter and oscillator.
It has an impedance of 1/jwC
(C is the capacitance, w is the freqency in rad/sec, j is the imaginary number)
Knowing the impedance, you can incorporate to any circuits and perform phasor analysis.

About electromagnetism, the component that's related to it is an inductor. It has an impedance of jwL
(w is the frequency in rad/sec, L is the inductance, j is the imaginary number)
Similar to a capacitance, you can also use it in a phasor analysis.

No offense, bud, but I could've gotten that from wiki or the like.

The rest of what you threw up was cool, but I think we need to keep this on topic of sorts. No need for us, and others, to throw up equations and their counterparts for the heck of it.

[icen]

Originally Posted by lostdaytomorrow

All future new guys reading this and thinking about buying a cap. to fix your bad voltage drops (Below 12v while car is running) or dimming headlights (common sign of non-adequate electrical system), keep in mind this will not help, and if it even seems to help (fixing your dimming headlights, which is not probable but stranger things have happened) it is not fixing the problem, but merely masking the problem. Your alternator is still being run full-bore at all times when the amp is drawing more current than the alternator can produce. Think of your car battery as a buffer and the alternator as the actual power source.

Yes, that is a very long sentence. Yes, caps can help with small voltage fluctuations. No, a cap should not be used instead of buying a high output alternator and deep cycle battery(ies).

Actually, IF you design the circuit properly, a capacitor and inductor together IS PHYSICALLY POSSIBLE to get rid of a MOMENTARY "voltage drops".
And of course, if it's not properly designed, it can damage the original circuit from the car because of back EMF.

Just take a look at the "buck converter" circuit. through the voltage regulating part of the circuit is not related to this, but the "voltage and current smoothing " part of the circuit can prevent that "voltage drop".

However, it is not practical because a huge capacitor and inductor is needed.

[icen]

o yea.. haha u r right,
Just got a bit too excited that someone actually is interested in electromagnets.. lol

[bikinpunk]

Originally Posted by icen

However, it is not practical because a huge capacitor and inductor is needed.

This is where my opinion comes in.

I don't think capacitors won't work... I just think that they won't do the job for most people and they most certainly shouldn't be the first "fix". They truly are a band-aid for dimming issues.
Bass-heavy music is much more taxing on your electrical that 'regular' music.

But, I think there's a lot more to our Civics than has been discussed. Such as the ELD that prevents the alt from supplying the battery with more power, thus causing the batt to max out @ 12.8v unless you 'tell' the alternator to kick things up by revving the engine or flashing your headlights. Lost saw this discussion in another forum. I asked about bypassing the ELD in the tech forum here but got no response.

[icen]

Well, don't think anything can fix that dimming issue, unless you increase the battery capacity, decrease the power consumption of other circuits, and decrease the use of inductors and capacitors... L and C effects the power factor, reducing the real power you can use. It's gonna be a system redesign.. -_-

I'm not too familiar with batteries.
But I heard from somewhere a few years ago, that battery life is proportional to how many voltage you charge the battery to. I think the relationship is exponential.
So your battery life might get a great cut if you consistently charge it up to a higher voltage.

[Phlipcyde]

With your lights on let your system run at full power on a constant bass note. If the lights dim for a split second and then return to normal brightness, a capacitor might help. If the lights dim and stay dim for the length of the note, you simply do not have an adequate supply of power, for which the only permanent solution would be a higher output alternator.

[lensam69]

DIY ALERT!!!!!


If you're going to do the following

Originally Posted by ameuba10

Before your charge your capacitor, you must discharge the capacitor. To do this, just short out the positive and ground leads very carefully and hold it for a few seconds to be sure that all the stored voltage is released.

USE A 5 ~ 10 W 4Ohm RESISTOR TO SHORT THE TERMINALS

Playing with a large capacitor is a lot like playing with a shotgun.. Even when you're 100% sure it's not loaded, you never point it at somebody!!!
Don't ever short the terminals of a large capacitor directly.

YouTube - Large High Voltage Capacitor Discharge

Those are my two cents to this conversation. Carry on...


(Oh, and my personal take is that large capacitors don't belong in a car... they belong in rail guns )
YouTube - 8 Capacitor Coil Gun

[ameuba10]

would this be sticky worthy?

[panthro]

kinda got lost half way through this thread...

will installing a capacitor help me to retain cleaner base? is it of any use at all?

and where does the fuse go? i assume it goes between that capacitor and the amplifier.

thanx

[ameuba10]

Originally Posted by panthro

kinda got lost half way through this thread...

will installing a capacitor help me to retain cleaner base? is it of any use at all?

and where does the fuse go? i assume it goes between that capacitor and the amplifier.

thanx

in no way would installing a capacitor help you retain cleaner bass. in the words of the great binkinpunk, "it acts like a bandaid." if you have the cash to do a big 3, there would be no need for a cap. if you have a system that draws id say, less than about 500w, you wouldnt need a cap. it is a cheap alternative if you dont plan on upgrading your alternator

[panthro]

preemptive apologies for my ignorance, but whats a big 3? and would it be a better idea to get a better battery if i dont want to do anything as extensive as replace an alternator.

MY system does draw a lot of power and i can hear it bottom out especially when the engine is on idle. revving up a bit seams to help it.