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PostPosted: Mon Mar 22, 2004 11:11 am 
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It seems that there is a lot of misconceptions as to the use of capacitors for car stereo use. I see the same questions/arguments coming up all the time on audio forums as well in the audio sections of non-audio forums. I guess people don't understand the use/proper implementation of the little devices that audio companies would have you think is the equivalent to adding a 100 shot of Nos to your audio system. Hope it all makes sense.

First and foremost. I am not against the use of a capacitor when used in the proper application. Capacitors (if used) should be used on vehicles where the charging system is more than able to power the requirements of the vehicle. In other words if your total, worst case scenario, current draw is 100A you should have an alternator that can output 110A-120A. If your current draw is 150A then you should have an alt capable of 165A-180A. You get the idea. I try to have (and these are my personal guidlines) around 10%-20% more amperage availabe then total amperage drawn. Some people actualy prefer 20%-30% more.

This next part has the two best explanation I have read yet. They are, again, members from another forum I'm on.

Yonzie wrote:
"Why caps don't do much good - the extremely short and basic version.

Let's imagine a car with a 12v battery and an alternator putting out 14v. This car also has a 1000watt amp powering some random sub.
We now add a 1 farad capacitor.

A 1 farad cap charged to 14v stores about 84 joules.
Since we have the battery sitting at 12v, the potential (useable power) of the cap is 2v or 12 joules.
We CANNOT use more than the 12 joules, since that would put the cap below the magical 12v where the battery kicks in.

In order to use the power stored in the cap, we would have to turn off the alternator, or the power it outputs would somehow have to drop - like if it's overloaded (BAD).

Note: 1 joule = 1 watt-second. 1000w for one second is 1000 joule.

Anyway, our 1 farad cap has 12 joules of power we can actually use. this translates into 12 watt-seconds. This can power our 1000w amp for 12/1000s of a second, or 0.012seconds.
This means that if we charge the cap to 14v, and turn off the alternator, we can play a single test tone of 83hz one single time before the cap becomes useless.

Since I'm not at all an expert on this, I have neglected to mention ESR and ESL, which would significantly reduce the benefit we get from the cap.
Because of ESR (ElectroStatic Resistance), an amount of power will be converted into heat in the cap. The more power you try to pull, the more heat and the less useful it is.
Additionally, the amp will convert some amount of power into heat - alle depending on the amp.

In the end, the cap may give us as much as .005 seconds (single 200hz tone) of power at 1000w amp output, IF the alternator suddenly dies or for some magical reason (it's overloaded, duh) it drops it's output to 12v. If you only run 500W, it would be about 0.01 second or a single 100hz test tone."


Here's another one...

defiance wrote:
Caps DON'T cover up problems with an electrical system. That's why they have such a bad name, that's what people TRY to use them for.

In fact, caps are best used with a more-than-capable charging system, and provide several benefits - most of which boil down to less stress on your charging system and amp (assuming it's a PWM power supply - more power otherwise). Why? Simple - because if your amp draws (sampled 3 times over a second) 20, then 80, then 20 amps, your main supply will have to send 20, then 65 or so, then 35 or so amps. Notice that the peak is cut off severely, because the capacitor supplements the current temporarily. Of course, the current draw increases later, totaling out to the same amount of overall current, but the increase is at a low-draw point, where it doesn't have as stressful of an effect. Thus, during peak points, your main power wire and charging system are asked to supply less current. As a result, voltage remains higher during peaks (even if you have 4/0 power wire, there is SOME voltage loss, and it will always be more loss at higher amperage - not to mention, the charging system will drop a bit during peak draw as well). Less current drawn during peaks= less stress to your alternator, and higher voltage present during peaks = less heat from your amp (or marginally more power).
This is all provable, testable fact, not opinion.
Now, having said this, you must notice: a capacitor on your system does not change the total current draw. Thus, if your alternator won't keep up, it STILL won't keep up with a cap. That's why they got a bad name, people using them in the wrong application.

AFTER you get your charging system fixed up, then put a cap on it if you have extra cash. It's a nice little device. No, it's not vital. No, it won't make an audible difference. But it will reduce stress & heat, and will probably make your amps, and possibly your alternator, live a while longer.


This link here is a test done by Richard Clark. It shows further proof to what a cap really does in your electrical system. It's also done with a 15F cap as opposed to a more common 1F-2F. These tests show that the usefulness of a cap is basically nil. It certainly doesn't do what audio companies say they will. Keep in mind also that even though the test was done in the year 2000 capacitor technology hasn't really made any leaps and bounds in the last four years. Most notable is just the actual increase in capacity they have. 100F nowadays is readily available in a single chassis.

So, bottom line, where does that leave us? Caps are absolutely not a necessity in a car audio system. Even after you have spent the money to upgrade the electrical system in your car they still don't do much. If you are looking to get that minuscule extra out of your system for an RTA (which I still doubt would do much) or extra points for a show car then by all means, yes, get a cap. For everything else...you can spend your money better elswhere.

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PostPosted: Sat Jun 05, 2004 10:31 am 
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I think you missed the point of the capacitor?

The Cap eliminates the AC waveform riding on the 12V DC bias of your electrical system. The wires alone will have a natural inductance in them, that resists the change in flow of current, that a sudden voltage drop would ask for.

So when the amp pounds and asks for 1000 amps spike for two nano seconds, the capacitor will instananeously fill the void while the electrons rush up the wire to meet the demand. It may only be a couple of joules, but the job of a capacitor is not that of a battery. It is not designed to "store" charge, its designed to absorb temporal spikes in + or - charge.

Take a look at your AC waveform before and after a 1F capaictor on a 12V system with the music cranked. Use an oscilliscpoe, you will see a major reduction, which means better audio quality.

Also keep in mind, that bigger caps, like 15F (is there such thing?), are TOO big to respond to instant (or high frequency) voltage drops. The smaller the capacitor, in particular when you leave electrolitic capictors out of this, the better the response. A small capacitor will be able to handle very high frequency current requests, but it will not have much power to back it. A bigger capacitor while "in theory" should be able to help out just as more, will actually be alot worse at higher frequency response because the wire acutally inside of it is TOO long, and it does take time before the electrons in it begin to flow.

Ideally you would want to have have an assortment of capacitors in your audio system. Like .5F Electrolitic, .25F MOS, .1 Tantalum etc. See here for a list of types:

http://users.telenet.be/educypedia/elec ... stypes.htm

This is why most manufactured capacitors for sale in store for your audio system are really just a collection of smaller capacitor networks in a nice casing. This ensures best performance, and believe me, it DOES make a difference in audio quality. It even helps to absorb the spikes on your 12V line from your ignition.

-Steve


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PostPosted: Sat Jun 05, 2004 2:42 pm 
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I agree with some of what you are saying...

BV1 wrote:
I think you missed the point of the capacitor?


I don't think so. I've explained why they don't do what audio companies claim they do. Audio companies would have you believe that the cap is there as a device to supplement your electrical system by supplying a burst of energy when your amps demend more current than what the electrical system is capable of. They aren't. They are there to smooth the voltage ripple.

BV1 wrote:
So when the amp pounds and asks for 1000 amps spike for two nano seconds, the capacitor will instananeously fill the void while the electrons rush up the wire to meet the demand.


Have you ever measured the length of a drumbeat? It's much longer than a nanosecond. Use a hip hop beat as your reference and some of them are straight tones of more than a second. Your saying here that the 10W-15W a 1F cap sends the 1000W amp to fill a void will actualy fill a gap that big? No way. The cap, as you said, is there to stabilize a ripple...not a big voltage drop.

BV1 wrote:
It is not designed to "store" charge, its designed to absorb temporal spikes in + or - charge.


No, a capacitor is a storage device. That's why you have to charge it and that's why the charge is stored until it's required by the electrical system (in this case a ripple). It differs from a battery in that it cannot make electrons but it is definetly a storage device. The farad reading on it is the indicator of how much capacity (to store energy) it has.

BV1 wrote:
Also keep in mind, that bigger caps, like 15F (is there such thing?), are TOO big to respond to instant (or high frequency) voltage drops. The smaller the capacitor, in particular when you leave electrolitic capictors out of this, the better the response. A small capacitor will be able to handle very high frequency current requests, but it will not have much power to back it. A bigger capacitor while "in theory" should be able to help out just as more, will actually be alot worse at higher frequency response because the wire acutally inside of it is TOO long, and it does take time before the electrons in it begin to flow.


If the resistance in the cap is the same it shouldn't react any slower than a smaller cap for it's intended purpose. This is where the problem exist and I think you are understanding it but explaining it in a difficult manner. You don't need more than 1F to smooth out the voltage going to an amp. In fact you need much less than that (which I will touch upon in a moment) to smooth it out. A 15F (or 50F or 100F) is marketed by audio companies as a faster acting battery for your amps. That is not what a capacitor was designed to do. We both agree on this and this is why I say that the only way a cap would benefit a system is when the electrical system is 100% able to power the stereo's current demands.

BV1 wrote:
This ensures best performance, and believe me, it DOES make a difference in audio quality.


If you can hear the difference that a 1F (or multiple smaller ones) cap makes to an audio system then I suggest working for an audio company where you will make millions. Amplifiers have capacitor banks in them to do just what you are saying adding a cap should do. You could argue that there isn't enough capacitance on board but if the electrical system of the car can supply the proper amount of current to the system the capacitance will be ample. It's been shown through blind tests, ABX comparisons, and RTA measurements that the differences a cap can make to sound quality, that you can actualy hear, are pretty much non existant. I wish I still had some of the tests because I wanted to add these to the FAQ. Unfortunately I only had RC's current charts. They basicaly show that if a $2500 pickup can't hear (or in this case see) the difference in frequency response then there is no way that the human could. You can, however, deduce from the findings of RC in his charts that there was a greater strain from having the capacitor wired up to the system in the typical manner that an audio company would advise you to do. This could actualy have a negative impact on sound quality. The strain we see in the charts would not be caused by the fact that the cap was 15F either.

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PostPosted: Fri Jun 18, 2004 9:50 am 
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Ahh I don't feel like writing a huge ass response. I will make some quick points that need to be made.

1st, sorry about my previous response, I didn't intend to present my tone with a negative demeanour.

When an amp pounds, the temporal voltage drop is about 2 nano seconds, the beat maybe alot longer, but the temporal void in your wiring to the amp is responable for the voltage drop, not the length of the beat. After 2 nano seconds the battery supplies enough current to restore the proper voltage. This number will vary on a number of factors.

However that temporary surge in current, causes a voltage drop, and then a spike. Think of it like a long hose of water. You ask for alot of water and it takes a second mefore all the water in the hose starts to move, and then you shut the tap, and all the water slams into it. The capacitor is like putting abucket at the end of the hose. In reference to the lake where the water is coming from, the bucket isn't much. But in reference to the hose the water is drawing on, the bucket is alot, and therefore, helps the hose conduct better, and makes up for any surges or lack of water in it.

The bottom line is, if you take a portable oscilloscope an look at your 12V line with reference to ground, at the amplifier, you will see an electrical difference before and after the cap.

You get:


----------------

or:

~~~~~~~~~

instead of:

-`-_-`-_-`-_-


No worries,

-Steve

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PostPosted: Fri Jun 18, 2004 12:23 pm 
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I have 2-1F caps and I too have always believed they are just there for "top up" during drum solos etc. My car sounds SOOOOOOOOO good they must be working! LOL I only run 200 watts (hee hee) so I don't have to worry about these 1000W scenerios :)

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PostPosted: Fri Jun 18, 2004 12:59 pm 
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BV1 wrote:

1st, sorry about my previous response, I didn't intend to present my tone with a negative demeanour.

-Steve


Steve, I didn't take your post in a negative way at all. I'm not gonna reply with huge post either except to say that the way a properly designed amplifier is built there is enough capacitance onboard to smooth voltage and account for the temporal voids. You will definetly see an electrical difference on the scope but this difference is filtered out in the amp.

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PostPosted: Fri Jun 18, 2004 6:42 pm 
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I've gone sideways LOTS of times and I could have sworn there was more places to go!!!!!!! LOL

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PostPosted: Sun Feb 01, 2009 2:34 pm 
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150dollarcar wrote:
thanks, that's not a really lengthy one, and it does leave things a little unclear. it's still a subject with more opinions than facts. the theory is all there, and I was actually wrong about a cap being better for a smaller charging system, but at the same time, no matter how much there is against a cap being a helpful part of a system, there is usually a noticeable difference in the rest of the electrical system of a car (not necessarily the audio system), when comparing with and without one.

thanks for the reference to that post, was just wondering your opinion.



My opinion is that they aren't needed. What part do you find unclear? The math is there to show why they can't do what they are claimed to be capable of.

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PostPosted: Mon Feb 02, 2009 4:29 pm 
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150dollarcar wrote:
thanks for the info. it's a bit brief, wish there was more. it seems a debate that has more opinions than facts as yet. it doesn't address the noticeable difference in the rest of a cars electrical system (not necessarily the audio system) with and without a cap. tghat's one thing I'm curious about, because you can usually see a difference, not necessarily hear it. I've also heard that a cap is supposed to boost a systems peak output power. probably something else said by manufacturers in order to make sales. doesn't make much sense to me. have you heard this before



I'm not sure how you aren't seeing the facts in here. Its written in plain english. Any noticeable difference on the rest of the vehicles electrical system is basicaly a band aid covering up a problem. The voltage drops and the headlights dim. The cap may have enough in it to lessen (or sometimes stop) the dimming but the root problem is still there. Your alternator is still not powerful enough to meet the current demands. Only way your going to boost a systems peak power is to raise the voltage (which won't do anything for you if the amp is tightly regulated)which the cap cannot do. If you have a huge 50-100F it may stabilize the voltage enough (though the test done by Richard Clark showed otherwise during his test...I'll see if I can find the graph as the link no longer works) but ultimately your electrical system should be able to output more current than what is required before a cap does what it was designed to do.

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PostPosted: Tue Feb 03, 2009 1:46 am 
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Ok Ok...

For the electrically dis-inclined... A capacitor is not a reserve source of power, it's a buffer... multi-stage capacitors are used to smooth out and keep voltage smooth... they do not act as small batteries, while they maintain a charge that charge is just to keep 12v clean, your drop the input power it drops. Capacitors drain a huge amount of energy when they are depleted, this is why if your Altenator isn't strong enough to power the system with stability, putting a cap in line, will kill it fast. This is because the cap has to allow the power the components are pulling go through but it has a parasitic effect in that it wants to refill up to it's optimum level.

Computers use capacitors wherever there is something pulling power, this is because the chips inside require DC line voltage, and they like their to be no dirt or wavering in that voltage. Caps clean, caps don't supply... That is why Caps don't do what you are claiming they do... :wink:

Line on a gauge without caps: -_-_-_-_- = noise

Line on a gauge with caps: --------- = less noise, the higher the farad rating the more noise they can filter from a higher throughput.

If your charging system is fully capable of handling the power requirement of the system, a cap will remove line noise and static. If your charging system isn't up to snuff, the capacitor will make it fry. :)

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PostPosted: Tue Feb 03, 2009 2:08 am 
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and, since your amp already has a capacitor bank inside it no need for big caps in a system either

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PostPosted: Tue Feb 03, 2009 3:08 am 
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Funny how this post has stayed alive and contraversial. :vibe:

I thought I would point out a few misunderstandings and misconceptions I've been reading above though.

First, the purpose of a capacitor in a DC system: In a DC system a capacitor has only one function and that is voltage support when wired in parallel to a power source. Capacitors appear as an open circuit to DC systems if wired in series which is done in analog circuitry to block DC bias signals (unwanted DC current). Capacitors are also used in filtering circuits (parallel or series configuration) but this applies to AC circuits ONLY.

If you believe my basic explanation above (and you should... :) ) then we can discuss why and why not to install a capacitor in a car (with or without a stereo).

If you install one amplifier and the manufacturer is not too cheap, they will install enough capacitors on the amp to support the voltage demands of the single amplifier. The manufacturer does not try to account for every charging system in every vehicle. They just assume you will provide the amp with proper voltage and current. Now if you install a second amp, the manufacturer is still making the same assumptions about proper voltage and current supply. Many cars do not have enough excess current supply to run multiple amps and now this assumption is incorrect. Try and draw too much current long enough and you get a fried alternator. Again, capacitors are voltage support, NOT current sources so in this scenario a capacitor does nothing to help you out. In fact, they require current from your alternator just like your battery to charge, this is where the argument that they actually hurt alternators comes from. Fairly speculative in my opinion.

Sapposing you have a big enough alternator to supply the constant current demand of your amps, pulling large amounts of current very quickly from your charging system (like during a big bass hit) WILL cause a voltage drop in your electrical system. The voltage drop can be calculated fairly easily utilizing differential equations and something like MatLab or MathCad software. In this scenario, a capacitor can be used to help support the system voltage. Add capacitance to your MatLab model and run it again. Do this iteratively until your voltage drop is acceptable. Applying an appropriate sized capacitor WILL HELP hold the system voltage above 12V and this is why your lights stop dimming. Back to the internal amp capacitors, in a multi-amp system the internal capacitors are generally not large enough to provide adequate voltage support due to design and space constraints. Adding a system capacitor adds another layer of voltage support on top of the internal capacitors. This is NOT a bad thing.

I am not about to argue that adding a capacitor to a low end system will make it sound like a show car, but for the price I add them just to make the lights stop dimming and the voltage regulator stop working so hard. For reference, I add .5F to a system with a total RMS output of about 300 watts. These 15F caps that people are selling are a bit rediculous. Unless you are pushing huge amounts of power anyhow. They are also quite dangerous in the right scenario, I hope people realize that!

Any more "factual" explination will have to come from your local community college electronics course or 4 year university I promise!

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PostPosted: Tue Feb 03, 2009 5:32 pm 
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akmetro wrote:
Funny how this post has stayed alive and contraversial. :vibe:

I thought I would point out a few misunderstandings and misconceptions I've been reading above though.

First, the purpose of a capacitor in a DC system: In a DC system a capacitor has only one function and that is voltage support when wired in parallel to a power source. Capacitors appear as an open circuit to DC systems if wired in series which is done in analog circuitry to block DC bias signals (unwanted DC current). Capacitors are also used in filtering circuits (parallel or series configuration) but this applies to AC circuits ONLY.


There are several inaccuracies here.

Capacitors appear as an open circuit to DC systems - true - but only when that DC is at a constant voltage, which it rarely is in either an automotive environment or an audio amplifier.

If you have access to an oscilloscope hook it up to a DC line and switch it so the input is capacitively coupled - feel free to use the +12V system in your car - take a look at the wave forms that exist on that 12V line and then switch the coupling so it's direct and reset the scope so you can see the trace - do you see more or less wave form with the cap or without it? All the cap does is allow you to remove the DC offset, the noise passes through the cap like if it wasn't there.

Capacitors are also used in filtering circuits ..... but this applies to AC circuits ONLY - take a look at any audio amplifier, there are going to be a couple of large filter caps in the power supply area - this is actually a DC circuit, not an AC circuit.

Caps are used in different circuits for different purposes - I've seen caps used to remove DC from AC circuits, and to remove AC (ripple) from DC circuits, I've seen caps used to filter low frequencies from high frequency circuits and to filter high frequencies from low frequency circuits. I've seen caps used to turn triangular waveforms into near pure sine waves

Last but not least - I've also seen caps used to supply standby power in exactly the same fashion as a nicad battery would be used (4.5 farads 3V, in an old JVC VHS recorder, feeding the timer and recording presets for almost 15 minutes after an outage) - I've seen them used to retract disk drive heads in a power failure (to prevent a head crash), I've seen them used in ATMs to eject your card in case of a power failure, so yes, caps are also used to supply power.

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PostPosted: Wed Feb 04, 2009 3:35 am 
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fordem wrote:
akmetro wrote:
Funny how this post has stayed alive and contraversial. :vibe:

I thought I would point out a few misunderstandings and misconceptions I've been reading above though.

First, the purpose of a capacitor in a DC system: In a DC system a capacitor has only one function and that is voltage support when wired in parallel to a power source. Capacitors appear as an open circuit to DC systems if wired in series which is done in analog circuitry to block DC bias signals (unwanted DC current). Capacitors are also used in filtering circuits (parallel or series configuration) but this applies to AC circuits ONLY.


There are several inaccuracies here.

Capacitors appear as an open circuit to DC systems - true - but only when that DC is at a constant voltage, which it rarely is in either an automotive environment or an audio amplifier.

If you have access to an oscilloscope hook it up to a DC line and switch it so the input is capacitively coupled - feel free to use the +12V system in your car - take a look at the wave forms that exist on that 12V line and then switch the coupling so it's direct and reset the scope so you can see the trace - do you see more or less wave form with the cap or without it? All the cap does is allow you to remove the DC offset, the noise passes through the cap like if it wasn't there.

Capacitors are also used in filtering circuits ..... but this applies to AC circuits ONLY - take a look at any audio amplifier, there are going to be a couple of large filter caps in the power supply area - this is actually a DC circuit, not an AC circuit.

Caps are used in different circuits for different purposes - I've seen caps used to remove DC from AC circuits, and to remove AC (ripple) from DC circuits, I've seen caps used to filter low frequencies from high frequency circuits and to filter high frequencies from low frequency circuits. I've seen caps used to turn triangular waveforms into near pure sine waves

Last but not least - I've also seen caps used to supply standby power in exactly the same fashion as a nicad battery would be used (4.5 farads 3V, in an old JVC VHS recorder, feeding the timer and recording presets for almost 15 minutes after an outage) - I've seen them used to retract disk drive heads in a power failure (to prevent a head crash), I've seen them used in ATMs to eject your card in case of a power failure, so yes, caps are also used to supply power.


No one is denying that a Capacitor can store and output power, hell I've seen all the warnings on the big caps they use for monitors, LCD and CRT. Caps can be used to store large burst currents(electric motor starter) and trickle currents(clock in the vhs player).

The issue at hand is people using them to feed systems, when the charging system can't keep up to the sound system without one, and thinking "Oh I can just install a cap or three, and badda bing, problem solved." The thing with that is though, is the system constantly pulls more than what can be supplied, and you have Capacitors adding a load, which is what blows up altenators and the like.

I'm foggy on the details since it's been awhile but for every amp that comes and goes through a capacitor you need 1.1-1.2 amps to output that 1 amp. Thats a 10-20% increase that really makes itself felt when you are constantly draining the caps and they are of course opening the taps bigger and bigger, and that leads to component failure.

Adding Caps to a system that is being properly supplied by the charging circuit is just doing a job twice. The only time you will notice any gains from it are when you are using poor equipment, since everything already has built in banks of capacitor to actively or passively control power fluctuation.

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PostPosted: Tue Feb 10, 2009 2:09 am 
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fordem wrote:
akmetro wrote:
Funny how this post has stayed alive and contraversial. :vibe:

I thought I would point out a few misunderstandings and misconceptions I've been reading above though.

First, the purpose of a capacitor in a DC system: In a DC system a capacitor has only one function and that is voltage support when wired in parallel to a power source. Capacitors appear as an open circuit to DC systems if wired in series which is done in analog circuitry to block DC bias signals (unwanted DC current). Capacitors are also used in filtering circuits (parallel or series configuration) but this applies to AC circuits ONLY.


There are several inaccuracies here.

Capacitors appear as an open circuit to DC systems - true - but only when that DC is at a constant voltage, which it rarely is in either an automotive environment or an audio amplifier.

If you have access to an oscilloscope hook it up to a DC line and switch it so the input is capacitively coupled - feel free to use the +12V system in your car - take a look at the wave forms that exist on that 12V line and then switch the coupling so it's direct and reset the scope so you can see the trace - do you see more or less wave form with the cap or without it? All the cap does is allow you to remove the DC offset, the noise passes through the cap like if it wasn't there.

Capacitors are also used in filtering circuits ..... but this applies to AC circuits ONLY - take a look at any audio amplifier, there are going to be a couple of large filter caps in the power supply area - this is actually a DC circuit, not an AC circuit.

Caps are used in different circuits for different purposes - I've seen caps used to remove DC from AC circuits, and to remove AC (ripple) from DC circuits, I've seen caps used to filter low frequencies from high frequency circuits and to filter high frequencies from low frequency circuits. I've seen caps used to turn triangular waveforms into near pure sine waves

Last but not least - I've also seen caps used to supply standby power in exactly the same fashion as a nicad battery would be used (4.5 farads 3V, in an old JVC VHS recorder, feeding the timer and recording presets for almost 15 minutes after an outage) - I've seen them used to retract disk drive heads in a power failure (to prevent a head crash), I've seen them used in ATMs to eject your card in case of a power failure, so yes, caps are also used to supply power.



My original post was made in the interest of providing information for folks without a good knowledge of AC/DC circuits so that they can properly apply capacitors to their audio systems. I stand by my original post and again will point out some things, let me know what you think.

"Capacitors appear as an open circuit to DC systems - true - but only when that DC is at a constant voltage, which it rarely is in either an automotive environment or an audio amplifier." - I constantly monitor my battery voltage in my car in it rarely differs more than +- .05 Volts. I would argue a system with much more than that has a faulty regulator? Putting a cap in series with your alternator would result in zero current flow once the cap charged (DO NOT DO THIS!)

"Capacitors are also used in filtering circuits ..... but this applies to AC circuits ONLY - take a look at any audio amplifier, there are going to be a couple of large filter caps in the power supply area - this is actually a DC circuit, not an AC circuit." - Maybe my original post was unclear, you are only partially correct here. If you can get your hands on a schematic for an amp board take a look, I suspect you will find the largest caps on the board are connected in parrallel with the main power supply terminal, these are voltage support capacitors which serve the same purpose as a cap added externally to your power system. Several smaller caps on the board will be used for filtering in both parallel and series arrangements. Also note, the board of an amp contains both AC (sound signals) and DC (power supply for your MOSFETs) circuits.

The last two paragraphs really don't seem to apply to stereo systems and would only seem to confuse those seeking info so i'll only comment on a sentence: "I've seen them used in ATMs to eject your card in case of a power failure, so yes, caps are also used to supply power" - This may be semantics but to say capacitors supply power is not true strictly speaking. A capacitor is a power storage device, like a battery. They should never be applied to an audio system for increasing available power. Conservation of energy is working against you, ie if you add a capacitor, the total power output of your electrical system is still constrained to the power output of your alternator, the only power supply in the system, the capacitor does not add to available power output.

Let me know your thoughts, specifically I'm curious if you are a proponent of caps in car audio or not?

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1994 xfi
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I really want a Turbo or GT Metro!


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PostPosted: Tue Feb 10, 2009 10:20 am 
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akmetro wrote:
I constantly monitor my battery voltage in my car in it rarely differs more than +- .05 Volts.


I guess you're using a DVM here - what is the response time of that DVM, how many samples per second does it take? Hang a 'scope in there and see what the actual waveforms look like - in particular take a look at the ignition coil's positive terminal, the one that is probably wired directly to the battery positive via the ignition switch and a fuse or two. Do it with the engine both off and on.

Quote:
Maybe my original post was unclear, you are only partially correct here. If you can get your hands on a schematic for an amp board take a look, I suspect you will find the largest caps on the board are connected in parrallel with the main power supply terminal, these are voltage support capacitors which serve the same purpose as a cap added externally to your power system. Several smaller caps on the board will be used for filtering in both parallel and series arrangements. Also note, the board of an amp contains both AC (sound signals) and DC (power supply for your MOSFETs) circuits.


I'll skip hunting down a schematic for now - but only because I have a long history in audio - not only repairing but re-engineering and building my own HiFi amplifiers, that predates ICE (In Car Entertainment), 8 track tape (remember those?), cassettes and CDs. Call it voltage support if you wish, but - take an AC powered amplifier and remove those caps from the circuit and see what happens - the hum will be audible in the output, and visible on the power supply rails if viewed with a 'scope - what they are doing is filtering the AC ripple.

I know you want to tell me that home audio and car audio are designed differently, but let's not get ahead of ourselves, I'm coming to that.

Now let's take a look inside the average hi-output car audio amplifier - note I said hi-output please. The limiting factor in power output in a car has been the "rail voltage" - with 12VDC, the available power is limited to V2/R (voltage squared, divided by resistance - sorry no superscripts) or with a 4 ohm load, 3 and some watts.

The first attempt to get around this was to use bridged output stages, connecting the load across two identical amplifiers and driving them out of phase, which effectively doubles the rail voltages and quadruples the available power, and then to DC-DC converters which boost the rail voltage itself by first switching the DC to a high-voltage, high-frequency AC voltage, and then rectifying it to get it back to DC. Can you see where this is going? Yes - we now have an AC power source, albeit at a higher frequency, but this time a square wave (think sine wave PLUS harmonics) and again we need to filter out the ripple.

What we have is capacitors being used in a DC circuit to remove or filter out the residual AC ripple.

Quote:
specifically I'm curious if you are a proponent of caps in car audio or not?


I'm not - I've tried them and I see them as having a function only in SPL situations, which I am not a proponent of. I've seen too many SPL systems that are built as show pieces and to win competitions and render the vehicle unable to used on a daily basis, much less as In Car Entertainment. I cringe when I hear a car drive by me, license plate rattling from the one note bass emanating whatever contraption the driver has in the trunk and if you're close enough the scratchy sound of a wall of cheap piezo horns.

Don't get me wrong - in my youth I walked the walk, building my own amplifiers, building subwoofers to complement studio monitors, had a tri-amped system with active cross-overs etc., etc,., but my focus was always on fidelity (or SQL if you like) a concept that seems to have gotten lost along the way. I had a "party wagon" with speakers in the tail gate and Fosgate amps under the seats - it's primary focus was not in car entertainment, but out of car entertainment.

I have a moderately sized system installed, a Panasonic head end driving Kenwood separates directly and a small subwoofer to augment the bottom end - it doesn't need a cap and the stock alternator is more than adequate.

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PostPosted: Sun Sep 06, 2009 10:12 pm 
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lol

Its just a bit of bling with a volt meter on them i understand that it would be an idea if u were like parked up for ages pumping music but in theory we should not be making the poor car need to get anything else in it. now i run a small system as i believe u look like a nob with to much power in such a little car that all it does is vibrate the living shite out of it. ive got a small pioneer setup and it powers it nice enough to keep everything happy and i can run that at full lights on and wipers and anything else i can get on and i still see no problems with voltage drops or any of the lights dimming. so maybe people should be out checking their earths ????

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PostPosted: Sun Aug 01, 2010 12:29 pm 
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I'm just passing through, shopping for large capacitors for sale in winnipeg actually, and found your discussion.

A cap IS a current storage device, so is a car battery.
Batteries are sold with different ampacities, but the same voltage output.
A power amp needs CURRENT to move the diaphram via the voice coil.
All the voltage in the world will not move a speaker coil if it doesn't have the required current to finish the job.
To believe this is about keeping voltage ripple off the power bus is... well you wouldn't have to worry about voltage if the current was available. Current will drop before voltage.
Besides, any amp will have inductive chokes inside the amp to remove AC off the DC bus.

To avoid loss of needed power you need a bigger alternator for more current output, more voltage is so very bad as the amp is built to use 13.5-14VDC. That's why alternators have built in voltage regulators.

Bigger the capacitor rating, the better. Period.
The RC-time constant formula cements that fact. T = R * C
R - resistance of the load of the amp on 12VDC power bus (not speaker-ohms) at any given moment of time
C - the unit of capacitance in microFarads.
Time is in seconds.
Since R is very small under load, we need a very large C in Farads, not microFarads.
The formula tells us how long before a capacitors charge is reduced by to 37% output.
http://www.tpub.com/neets/book2/3d.htm

So, as amp draws more power,Watts are increasing,
V * I = Watts = I(squared) * R,
V is constant (or supposed to be)
I is increasing exponetially, so R is decreasing proportionatly.

R*C, where C is fixed, so when the R is decreased, T becomes smaller, the cap discharges faster, and less charge available to draw from for the amp to pull the voice coil back for the alternate cycle of the coil movement and following push-pull cycles.
But, if we increase C, that changes the formula for a longer dis-charge cycle, and more boom-boom for you.

Note that the Charge/discharge cycle is a two-way street.
The Charge resistance R, is the wire resistance from your alternator, (without consideration to any effects of inductance to an LC-time constant), forgiving the amp drawing against total available current while you are trying to charge the cap.
So, to get the benefit of a stupid-huge cap, you need either bigger wires, or shorter wires, or both, assuming you have a alternator capable of supplying more than you can use in current.

Here are illustrations of people who get this concept:
http://www.youtube.com/watch?v=RRDA64OegJY
http://www.youtube.com/watch?v=r1tDElOuLCw
Quote:
30,000 - 50,000 watt set-up with 5-super high output alternators with a bank of batteries in the back to provide the 2500-amp draw of the linears. Vehicle has 454/w nitrous. For keydown leave it in park floor it hit the amp and nitrous´╗┐ at the same time so the motor wont stall out and you have time for a 5-7 second keydown before you pass-out from rf burns.

70,000 watts:
http://www.youtube.com/watch?v=JTW3LmM7qBA
Quote:
extremes of a hobby. puttin out 20,000 more watts than the big clear channel commercial AM stations like WOWO. I saw the le clip of this from a guy who was also cam-cording and the guy who did this tape 75 feet away when he keys down then the camcorder went blank and ejected the tape. the dude inside said his vision gets so badly effected that he can barely see when he's keyin this´╗┐ thing down.


Once everything else has been considered and addressed, then yes, there is the law of diminishing returns. But then I think a 1000Watt sub-woofer has already past that point.

How about instead of just "more power", try a different type of speaker like this:

http://www.youtube.com/watch?v=0sne_uI2Yq4
http://www.youtube.com/watch?v=2Lr8tVC-Qx0
http://www.youtube.com/watch?v=YyVTvtgm11o


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PostPosted: Mon Aug 07, 2017 4:58 am 
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Joined: Mon Aug 07, 2017 2:42 am
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do you think is a lot of work to put the whole engine in??? did it get on the 4wd gearbox??? what about the electric sistem???

gclub


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