# Capacitor & Distribution Block Question



## Rboussey (Sep 21, 2012)

I'm running 0 gauge wire from the front battery to my trunk then having a distribution block going out to 2, 4 gauge wires leading to 1 amp for my sub woofers and another amp for all 4 door speakers. I want to install a capacitor but I'm not sure if I should get one large 1 to go in front of the distribution block or 2 smaller ones after the distribution block for each amp? 

Here's a picture to clarify what I mean:


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## jhsellers (Jan 7, 2012)

Rboussey said:


> I'm running 0 gauge wire from the front battery to my trunk then having a distribution block going out to 2, 4 gauge wires leading to 1 amp for my sub woofers and another amp for all 4 door speakers. I want to install a capacitor but I'm not sure if I should get one large 1 to go in front of the distribution block or 2 smaller ones after the distribution block for each amp?




IF - truly, this is a BIG if - you feel the need to install a capacitor, then the two scenarios you describe are equal, assuming larger size is the same as the two smaller ones added together. Capacitance is additive when paralleled. 

But, your picture is a bit misleading as far as actual connections are concerned. At least, it is for a capacitor applied per your question. The two terminals on a capacitor are not IN and OUT in this situation. The positive terminal is connected to the +DC line, the negative terminal gets grounded. 

I suggest you do some more reading about capacitors, before deciding that you really need one or not. 

Hope this helps,
John


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## nineball (Jan 17, 2008)

they are a waste of money. no need to read about them. be certain to fuse your 0g line within 18" of the battery as well.


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## MarkZ (Dec 5, 2005)

We've had a million capacitor "debates" in this forum over the years, and there's never been a consensus about how useful they are. We know _exactly_ how they work, and _exactly _how car electrical systems work, but nobody can ever agree on whether or not capacitors are worth installing, or under what conditions they might be useful.

I agree with the others above that you should hold off on adding a capacitor until you discover a specific symptom that you need to address (like dimming lights).

But you didn't ask that. 

To answer your question, there shouldn't be much of a difference between whether you get one big one or two little ones. EXCEPT that the ESR and ESL of the smaller capacitors are going to be smaller, all else being equal. [the ESR and ESL are numbers that describe how well the capacitor can discharge its energy to the electrical system at fast rates -- the smaller the number, the better] This is why you often see small capacitors in parallel with big capacitors in power supplies.


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## nineball (Jan 17, 2008)

After studying a little history on large 1 Farad capacitors in car audio, you'd be amazed that they even sell at all. How useful are they? What do they really do? Will a Cap 'improve' my sound quality? Will it Prevent my lights from dimming? Will it audibly affect my audio system in any way?

Before you get the truth to any of the above questions, chances are, you've probably spent $100 or more on one of these devices. However, let's study a little history regarding this issue.

A long time ago, in a land far away, 2 elves...Ok, Richard Clark & Wayne Harris (Carsound magazine and the inventor of DB Drag, respectively) separately came up with a solution to preventing their lights from dimming.

WHO WERE THESE GUYZ?

As you may know, Richard Clark is one of the founders of autosound2000 Tech Briefs, Carsound magazine, and a published author of the industry of mobile electronics. In SQ competitions, he posted a record of 1234 1st place finishes, and only ended up NOT 1st in his first event. I've heard that he had minor system problems, but judging by his record, he must have corrected it. (evidently, he needed a Capacitor )

Wayne Harris was previously a leader at Rockford Fosgate in their development. Later, in his free time, he created the organization we call DB DRAG. Wayne was the first SQ World Champion from the organization we know as IASCA (International AutoSound Challenge Association).

Both of these gurus are both legends, and considered the leading experts in the field. During their competition days, both guyz came up with a way to assist in the prevention of voltage drops. In SQ competitions, the look of your system is actually more important than the sound, and having your lights NOT dim under high playing levels is a competitive advantage.

As you may know, amplifiers are made up a bank of little capacitors, resistors, etc. What has been common engineering knowledge is that capacitors store energy, and more or bigger ones assist in balancing the power supply.

Wayne came up with the idea of putting several dozen 'little' (approx 100uF) capacitors on a circuit board to 'extend' the power supplies storage. At about the same time, or shortly afterward, Richard came up with the idea of one huge mondo capacitor (I believe it was 800,000uF or 0.8F) to do the job.

Eventually, Richard won. The large cylindrical tubes won over the complicated 48 caps strapped to a circuit board. However, what did this really accomplish? Let's start here:

WHAT IS A CAPACITOR?

Basically, capacitors are an energy storage device. Large, 1 Farad or more
capacitors store energy (electrons) between their plates. Capacitors differ
from batteries because batteries store energy in the form of chemical
energy--and rely on acid and lead plates, as the place of storage. For a more detailed
description of a capacitor, go here:

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

Then on the right hand side, scroll down to CAPACITOR. Keep in mind the use
of capacitors in an audio system.

WHY DO PEOPLE BUY CAPACITORS?

The number 1 reason would have to be because their lights dim when their
system is playing HARD. In car audio, we are told that a capacitor is
designed to prevent the voltage drop associated with your lights dimming.
The number2 reason is that it is rumored to 'improve' sound quality or
'stiffen' the power supply/source.

WHY DO MY LIGHTS DIM?

Headlights brightness is in direct proportion to the source voltage. For
instance, if your car is running, system voltage is ~12.5 -14.4 VOLTS. Your
lights will be much brighter than when your car is turned off--where battery
voltage is ~12V. Most car alternators put out between 75 to 120 amps of
current. When this current draw threshold of the charging system is
exceeded, system voltage will drop as power demands are now shared by the
alternator and the storage devices (battery & cap). We are using battery
reserves beyond this point until the demand lessens

When playing your system really hard. Your lights dim because your
alternator can't keep up it's charging voltage (around 13.5V) and therefore,
demand exceeds output. When this happens, your electronic devices are
dipping into the power storage of the battery. Since the battery stores
power at ~ 12-12.5V, there is a 1.3 to 1.8V drop in voltage available. This
in turn is why your lights dim down.

HOW MUCH POWER DOES A CAPACITOR STORE?

1 Farad = 100 joules or 100W/second
850cca battery = ~2,200,000 farads

For storage purposes, you'd need ~2,200 1 Farad capacitors to equal the energy of your battery.

Due to its impedence (ESR & ESL), a cap's energy is only 50% available. What's worse, is that in order for a 1 Farad cap to discharge, first the alternator output must have maxed out, and the voltage must have dropped around 1.5 volts. But I thought a cap was supposed to prevent that (voltage drop)!!!!!????? Yep, you got the point.


IF A BATTERY = 2,200 CAPS, THEN WHY BUY A (PUNY) CAP?

My question exactly. Marketing is the reason why people buy caps. In many cases, upgrading wiring will help your system get the maximum transfer of current. Once that has been reached, adding a capacitor may have a minor effect on your system. 50W over the course of a second is not a lot of power considering an amplifier may draw 2000W to put out 1400 watts. Let's look at the situation from a resources standpoint.

Alternator 80 amps
Car accessories (minus stereo) 40 amps
A large Car Audio system (DRAWS ) ~200 amps AT FULL OUTPUT

In this case, you have 240 amps of draw, but only 80 amps of current from the alternator. In your case, you need 160 amps x 12 volts or or let's say 1920 watts of energy. Since a cap stores 50W, how much of a difference do you think it's going to make? A cap is basically a peashooter. W+e need a Howitzer cannon here, to do the job well.

Also, Once a cap is discharged, where does it get it's power from? The alternator, which is already overloaded. Once a cap is discharged, it's worthless. Like SWEZ says, ・.The cap already shot its wad, an does limp til recharged・ I知 not so certain I will allow him to babysit my kids, but you get the drift. (I never said it quiet like that... and oh...I'm great with kids!)

SO, WHAT IS A CAPACITOR GOOD FOR?

1. Audio Jewelry- impress chicks with large cylindrical shiny thingy
2. Extra weight in winter time
3. A very POOR... BUT expensive distribution block
4. A projectile in the event of a crash
5. Rolling pin--for cooking purposes
6. A neat thing to tell your friend, "..Hey man, lick the top of this..


Please do not try # 6. New hairstyles are always refreshing, but if you are wearing railroad tracks across your teeth, you might have one big filling after it痴 over.

HOW CAN CAPACITORS IMPROVE SOUND QUALITY?

They can't. Sound quality is not dependant upon the presence of large bulky 1 Farad capacitors. How many 1 Farad Capacitors do you think the Boston Pops, Aerosmith, or Snoop dog use in the recording studio?

IN A NUTSHELL.......

When Richard, our fearless inventor, became World renown for winning every competition under the sun, people began copying what he did. Soon, every 'serious' competitor had a 'stiffening' capacitor--not to be confused with the 'loosening' capacitor.

WHY?

In the late 80s, people began sticking out their tongue when dunking the basketball because Michael Jordan did. Did sticking out your tongue improve your dunking ability? Same here with adding a capacitor to your electrical system.

STILL A GLUTTON FOR MORE PUNISHMENT?

Here's the Original Cap Debate.

http://www.carsound.com/ubb/Archives...-1-000307.html

Phoenix Gold's marketing guru had just posted information on how their Powercore (basically the Alumapro CAP15 in a Phoenix shell) had both stabilized their voltage and improved the sound quality. Richard called him on it (all in another post) and the marketing geek was unable to quantify any of the conditions that resulted in the voltage being HELD at 14.2V and the 'improved' sound quality.

Please do not read every stinking post as valid. There are a lot of people that have had the efficacy of capacitors inbred to their minds, and were not (and still not) convinced in the futility of a 1 Farad storage device.

In a final note, Richard relayed a quote regarding battcaps ( www.battcap.net ) as, "..The audio industry is the only place i know of where you can publish specs that show your product is useless and still be able to sell them------and whats worse is that technically ignorant people will argue against the math!!!!!!!..............RC.." when referring to the product. This also relates to most digital readout capacitors, and I wish my Archie Bunker skills could have said it better myself.


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## MarkZ (Dec 5, 2005)

nineball said:


> IF A BATTERY = 2,200 CAPS, THEN WHY BUY A (PUNY) CAP?


This is the conclusion (by whoever wrote what you pasted here). But they answer their own question here:



> Since the battery stores power at ~ 12-12.5V, there is a 1.3 to 1.8V drop in voltage available. This in turn is why your lights dim down.


So "why buy a puny cap"? The answer is easy: _because the battery cannot adjust its operating voltage to meet the operating voltage of the alternator, whereas a capacitor can._

When the goal is to reduce headlight dimming, it's not important that you supply all the current the amplifier needs with a capacitor. All you need to do is soften (or prolong) the dip in voltage to reduce its effect on our visual systems. The point is to exploit the fact that we're really good at detecting abrupt changes in illumination, but not as good at noticing more gradual changes. A capacitor used in this way is a lowpass filter... If you can lowpass your headlights, you'll reduce the percept of dimming. It would be even more effective if you could lowpass the headlights directly, but that's a topic for another day. 

Anyway... OP: install your system and see if you have headlight dimming before you bother dealing with any of this.


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## qwertydude (Dec 22, 2008)

Generally if you think you need a cap to prevent dimming, you could always go the second battery route. Put a good second battery in the back like a AGM battery which can discharge a lot of current. Then in order to charge that battery you can run a thinner wire from the front to the back like a 12 gauge wire. The reason for this is the wire will limit just how much power can be transferred from the front to the back by dropping voltage, when the wire drops voltage the second battery will be supplying the power to the amps. That way you're not pulling much power from the front.

Music works kinda funny in that you have to design the system for the peaks, but if you average it out you don't need that much current capability. Rockford figured this out on their new hybrid amps. Their fancy regulated energy storage device works similar to my AGM and thin wire to limit current spikes.


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## donnieL72 (Jun 20, 2012)

qwertydude said:


> Generally if you think you need a cap to prevent dimming, you could always go the second battery route. Put a good second battery in the back like a AGM battery which can discharge a lot of current. Then in order to charge that battery you can run a thinner wire from the front to the back like a 12 gauge wire. The reason for this is the wire will limit just how much power can be transferred from the front to the back by dropping voltage, when the wire drops voltage the second battery will be supplying the power to the amps. That way you're not pulling much power from the front.
> 
> 
> > Bad idea. Very bad idea.....
> ...


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## minbari (Mar 3, 2011)

donnieL72 said:


> qwertydude said:
> 
> 
> > Generally if you think you need a cap to prevent dimming, you could always go the second battery route. Put a good second battery in the back like a AGM battery which can discharge a lot of current. Then in order to charge that battery you can run a thinner wire from the front to the back like a 12 gauge wire. The reason for this is the wire will limit just how much power can be transferred from the front to the back by dropping voltage, when the wire drops voltage the second battery will be supplying the power to the amps. That way you're not pulling much power from the front.
> ...


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## qwertydude (Dec 22, 2008)

The wire will only carry as much current as the difference between the second battery voltage and the alternator. Given a fully charged lead acid battery of 12.6 volts and a running alternator voltage of 14.4 volts this means at most you can only have a 1.8 volt voltage differential across front and rear batteries until the rear battery supplies all the current for the amps instead of the alternator.

Given a 15 foot length of 12 gauge wire at .001588 ohms per foot, you're looking at a maximum theoretical current of 75 amps before all 1.8 volt difference is dissipated in the wire. In reality because of the maximum power transfer theorem, and the voltage rise of a charging lead acid battery, you're not going to be pulling anywhere near that you'll be pulling around 25 amps from the front because the AGM will be supplying most of the peak current limiting average current from front to rear to around 25 amps which is within the wire's capability. 

Believe me I tried it. If it really pulled enough to get dangerously hot I would have blown the 25 amps fuse long ago on my previous high powered builds when I was broke and couldn't afford to put a high powered alternator on my car.

Also when testing my car amps at home I use short lengths of 12 gauge to connect it to my power supply since it's nearly impossible to use thicker gauges without the risk of shorting out the contacts because the contacts are spaced closely. Even at 100 amps of current draw the wire doesn't get appreciably warm so a longer length at the same current wouldn't get any warmer than a shorter length, sure it would technically be dissipating more power but it's doing so over a greater length so the overall wire temperature stays pretty much the same.

But all the above still really wouldn't matter as the 12 gauge is fused at 25 amps so if you did exceed the current capability of the wire the fuse would blow.


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## donnieL72 (Jun 20, 2012)

The audio system runs off of the alternator until the amperage exceeds the alternator output. The simple fact that you have a battery in the rear is irrelevant. The current capacity of the wire running to the rear of the vehicle needs to be big enough to run the whole system. The rear battery is only a buffer. The thought that the amplifiers will only pull current from the rear battery is a push at best. When the audio system hits a big transient and demands high current, it will try to pull current from anywhere it can. That would mean both front and rear batteries. 

Wire size should never be used to limit current.

To the OP, I appologise for the thread hijack. 
I have said my peace here


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## MarkZ (Dec 5, 2005)

His implementation is wrong, but he's right that increasing the resistance of sources reduces the current draw. That's what Ohm's law tells us. If you have parallel sources (alternator, battery, second battery), and you change the ratio of their internal resistances (incl. wire), you alter current draw proportionally. There's no guesswork and subjective opinions about that. It's all math. 

I think it's more useful to take that knowledge and apply it in a different way, however. I usually suggest that people who have dimming headlights problems install their capacitor as (electrically) close to the headlights as possible, to minimize the resistance between cap and headlight while maximizing the resistance between cap and the rest of the electrical system. Maybe under the hood at the junction box, assuming there's space and the cap is rated for the temp. Hell, you could go full out and install a big inductor in front of the cap so that you can create a 2nd order lowpass.


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## sqshoestring (Jun 19, 2007)

I like this part of the paste:


> Alternator 80 amps
> Car accessories (minus stereo) 40 amps
> A large Car Audio system (DRAWS ) ~200 amps AT FULL OUTPUT


Not untrue maybe, but like everyone has a LARGE system that pulls 200A. I had a (tiny?) kicker 700.5 running 4x70rms and 1x420rms and it showed a max of 74A peak on a clamp meter and 30-40A rms. I was playing a bass CD full of sines full bore on the subs and just under clipping on highs (the amp had to be clipping on subs). The subs were rated for 600rms, but curious the subs never distorted that much no matter where the gain was. It had a 5ga wire from the battery (good for 860w class AB and 1075w class D according to bcae1.com), and that amp was class D on sub class AB on 4ch. Only did it for testing I never played it that hard.

200A will be ~1700w class AB or 2Kw+ class D....and using all of it.

That said with the kicker amp my headlights would dim if I had the AC on and brake lights on at a stop in drive. It was not very noticeable while driving unless you looked for it, and because this car tends to idle pretty slow. 125A alt.

Anyway a cap might make a difference with my dimming because it is barely dimming and would not take much to stop it. Now I have 4x125 (but 2ch are turned down) and 500rms on subs, but never have hammered it at night enough to notice any dimming since I put these amps in. I have a cap too, but its on my test bench instead of in the car lol. It was $15 off ebay.

I've also been told (by a tech) some old amps had weak power supplies because of two reasons: one it protected the amplifier section when overdriven so it could not exceed the output's ratings, and second because power supplies were harder to make before MOSFETS came along. Today amps tend to have a smaller power supply that makes more power and can easily deliver what the amplifier section requires....if designed to do so. So there may have been a greater need/effect with caps in the good old days because of that.

I've also read that you should put the cap near the headlights in an effort to have voltage drop more at the amps rather than the lights. I'm more interested in putting a cap on the remote wire to delay the HU from turning off so fast lol. That 1f cap will run the HU for a while, it may run it too long on the remote wire.


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