capacitors

[steve_protege]

Id like to know what exactly capacitors do? I hear people saying that they really help their sound systems and if thats the case, id be interested in gettin one also. I want to find out a couple things about it first though. Who makes good capacitors? Whats the difference between, say a 1/2 farad cap and a 1 farad cap? Can someone help me out here?

[goldstar]

Re: capacitors

A capacitor is a device that stores an electrical charge in a direct current (DC) circuit. As used in an automotve electrical system, its function is to maintain a stable voltage level in a circuit by "smoothing out" voltage variations caused by a temporary, heavier than normal current demand placed upon the circuit by, for example, an audio system at full output.

For example, assume the alternator is delivering 13.5 V to the circuit. Ignoring capacitor losses, the cap is also charged to 13.5 V. Now assume the bass kicks in on the audio system and the extra load it imposes drops the circuit voltage to 12 V. This can result in dimming of lights, etc. However the cap, which has been previously charged to 13.5 V, will now release some of its charge into the circuit, thereby momentarily raising the circuit voltage back towards 13.5 V. The cap, therefore, acts to stabilize the voltage level to some degree, hopefully reducing or preventing dimming and maintaining full bass output. After the heavy current draw ends, the circuit voltage will return to 13.5 V and recharge the cap back to that level.

The Farad (F) is the unit of measurement of the storage capacity of a cap-the amount of electrical charge it can hold. As such, a 1 Farad cap has twice the storage capacity of a 1/2 F cap. Supposedly, using a cap with more Farads, or multiple caps, will act to further reduce voltage drop and provide more stability in a circuit. Although this is the theory behind cap use, not everyone agrees that it is effective.

02 DX Millenium Red

[steve_protege]

So in your opinion, Goldstar, is a cap a good investment for a sound system? What would be the best cap to get and recommended farads to have?

[walight01]

its recommended 500 watts per 1/2 farad. as stated above, they are to maintain voltage. The only true way to maintain voltage is to have a alt that can power the car and entire system. if you are having light dimming problems,they are a bandaid fix for them. The same fix can be done by upgrading your ground wires on your car, and the power wire from the bat to the alt, bat to the fuse box. on low powered systems, caps can help out to maintain voltage, but on high powered systems, they don't do much at all. The money you would put towards a cap, put towards a battery and upgraded wiring. caps are a reallly great idea, they just can't hold enough charge to do alot. there is a product called a batcap, which is a cap, but holds enough charge to be considered a battery. the run like 170 bucks and up. lightning audio/RF make the best caps, mostly b/c they are owened by the same company.

[goldstar]

steve_protege

Unfortunately, since I only have the stock audio system, I can't help you with your questions having never used caps myself for this purpose. However, there are many audio experts here that I'm sure could help you.

02 DX Millenium Red

[hihoslva]

Steve - don't waste your money.

See, your alternator has the job of charging your battery, and running the electronics of the car.

If your lights are dimming from the stereo (and ONLY from the stereo), it is because your alternator is over-taxed and not supplying enough voltage.

Now, a cap discharges very quickly - VERY quickly. One 2 second bass hit can discharge a cap significantly. So while that bass hit *might* have come in "stronger" or not caused dimming lights, what about the next one? The cap may still be charging, and therefore not able to provide the voltage. And now your alternator is taxed even MORE because it has to run the stereo AND charge the cap. See?

Slight light dimming is a NORMAL attribute of a car's electrical system. Tonight, go out, run the car, put the headlights on, and turn on your A/C (or defroster so the A/C compressor clicks on and off). Don't your lights dim slightly when the compressor kicks on?

Or, pull up on two power window switches at the same time - you'll see some good dimming.

A capacitor on the AUDIO system is not going to solve this. It's normal. If you're worried about dimming lights, you need to put capacitors ON the lights.

As far as audible differences with a cap and without - doubtful. Are there differences? Yeah, especially once you get over 1000 watts or so. Can you hear the differences? In all probability, not at all. They could be measured with test equipment, but you won't hear anything "better" unless you have either the best ears on the planet or a car that is sound deadened to the point of hearing NOTHING from the outside world.

Remember, at 70 mph with the windows open, none of this crap makes any difference.

Caps are useful to SPL (sound pressure) competitors, who fight for every last tenth of a decibel, trying to be the loudest.

But for a daily driver with a nice upgraded system (that you play MUSIC on; not test tones), the money spent on a capacitor would be far better served buying upgraded speakers, amplifiers, or a better head unit. You'll get MUCH more for your money.

Or buy a savings bond.

~HH

[steve_protege]

Thanks for the heads up man. I didn't really see the point of a capacitor besides to get better bass and less dimming of the headlights. Im not going to be in any kind stereo competiton soon, so I guess a cap would be pointless. I suppose that if I want bigger and better bass I should just save up to get a better amp and bigger subs. Oh well. Thanks again everyone who responded.

[walight01]

actually caps provide no spl. blue had a link a while back that showed a test with a 2000k watt system with and without a 15 farad cap. it did absolutly nothing,

[JJB]

In addition to what HH said, the time constant of a capacitor also comes into play. The intial charge and discharge occur very quickly and then the final charge takes a while.

So... that big ol' bass note hits for a quick time, the alternator can not provide the instanteneous current (not voltage) which then results in a voltage drop in the system... however, since there was a charge storage right near the amp (the cap) and it is on a lower inductance lead than the alternator (short wire close to the amp) it delivers the required charge out. This is all well and good... and for that moment when the amp slugged power it did help out, but now it also needs to recharge itself and (if you managed to get a good amount of charge out the cap) that can present a much bigger load than the amplifier to the battery/alternator system. So you get what?... yup, dimming lights agaim... it's just not the amp demanding the power.

Now, for most systems the capacitor can be made large enough to handle the amount of instaneous current that the amp can draw (which is where I assume the rule of thumb that walight01 posted likely originated). But, this is really for just times when you are not continually demanding a lot of power from the amplifiers (i.e. the occasional bass note)... in an SPL competition (from what I have seen) the draw required from the system is pretty darn big and for a relatively long period of time (as compared to your regular tunes) and in that case the cap might even hinder the system... as once you get a cap to really discharge it can present a very high load to the alternator (almost a short circuit in fact).

I will have to proof this over some other time when there is not so much in my system.

[blue LEDz]

great info in this thread the whole 1 farad per 1000 watts is total crap, IMO. you'd need more like 5 farad per 1000 watts to really notice a difference. there are only like 2 or 3 manufacturers of capacitors, 4 or 5 including the "super caps". the difference between a several hundred dollar brax cap and a $50 boss cap, is how efficient they are. since they can't hold a lot of power, the less efficient they are, the less they do. but it still comes down to a fraction of a second difference. in some SPL applications caps have been proven to help, but they only help for that initial 1/10 second burst, and the number of caps requireds is insane. that is one of the reasons why most extreme competitors run off a 16 volt battery system, so the audio system is running off over 16 volts, getting maximum power out of the amps in the cap test that i showed that richard clark performed, the cap actually hurt the system, since the cap was an extra load, and the alternator couldn't reach as high of a voltage as without a cap now if you want to install a cap to get rid of headlight dimming, don't bother. it's a waste of money, and even misterT has a 1.5 farad cap on his system, and it doesn't help much, if at all but i am working on finding a one way diode or rectifier that will allow me to make a device that you'd be able to plug it inline with each headlight, and then each headlight would get it's own cap, dedicated to it the one-way diode or rectifier is needed, so that the system can't draw current from them, and the cap is isolated to the headlights

[goldstar]

Diodes

blue LEDz,

That's an interesting idea you have about using diodes in conjunction with caps. Let us know how it would work. I know your parts sources are better than mine, but I came across some diodes that you might find useful. They are fast recovery diodes available in ratings up to 150 AMPS and are made by Fairchild Semiconductor. They can be obtained from: www.mouser.com

I hope that you find this helpful.

[MisterT]

Just going to give you my 2 cents on what I did to try and stop or reduce dimming and it has not helped:

4 Gauge groundkit. I have it grounded all over the engine bay.

4 Gauge upgrade from alternator to the fuse box, and fuse box to the battery.

Deep Cycle battery with over 1000 CCAs (IMO not a waste of money considering how much electrical system is taxed)

4 Gauge wire going from battery to a power distribution block to a 1.5 farad cap

Class D amp for the subs to replace an inefficient Class A amp (which helped some)

All of this and the stereo still dims head lights. The alternator is weak and if you do decide to replace it, it is very tricky to do so in that it must work with the ECU. A lot of people drive around with the service engine light on because they can't plug the ECU plug in with the alternator. I just live with the slight dimming because I have tried just about every thing and spent a good chunk of change. The other thing too, is that because I have dual voice coil subs running at 1 ohm, it is drawing more current than say if I was driving a pair of 4 ohm subs. If I could some how trade my subs in for single ohm subs, it would be interesting to see if that would help some what with the dimming.

Rider69 (I think it was him) made a good point before I spent hundreds of dollars trying to eliminate as much dimming as possible. He mentioned to drive around a few minutes before getting to your destination without the radio on or atleast playing at a low volume to allow proper charging of the battery after long sessions of jamming. In this case, you won't drain your battery only to kill it by the next time you try and start your car up.

[blue LEDz]

goldstar, didn't you post that link on mazdamp3? my screen name over there is got wake? i'm checking into them, and am waiting a reply to my e-mail about which would work for my application

[jnorion]

I've replaced the entire stereo system in my 03 lx with high quality components. I have no sub, but I have a 320watt amp on the main speakers. When I first installed it, the lights dimmed noticeably when I turned the stereo on. I put in a 1/2 farad Rockford cap in and the lights are fine now. However, my system is aimed more for clear sound than loud sound, and I've never tried it with a sub. I don't have a competition system, I just like my music to sound good. I only spent about $70 on the cap, though, so it's cheaper than redoing the entire electrical system. It really just depends on what you want out of it.

[goldstar]

Re: Diodes

blue LEDz,

Yes, I did post that same link on mazdamp3. I didn't realize that you are also got wake?, so I decided to post it again here.


02 DX Millenium Red