# Grounding through Capacitor



## elvisjer (May 13, 2008)

Hey everyone! Partsexpress had the capacitor toppers that are distro blocks on sale for $7 so i bought one and am wondering about grounding. Is it better to ground amps to the distroblock on the cap, or directly to the chassis? Since i started my re-wire i've been having some odd popping and RF sounds, im wondering if it is from grounding to the cap. Thanks!


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## TXwrxWagon (Sep 26, 2008)

$7 is the only saving grace to why you are putting i a cap to begin with...

Why a cap? is there a "problem" you are trying to fix? or was it a "heck its cheap, let's try it" experiment... A cap is no different to the alternator than another amp, processor, battery or fancy blinking lights... its a load. It won't "fix" anything. It will temporarily stop major issues.. but not fix them.

if your alternator & entire electrical system is up to par, then yes there is a SMALL benefit to a cap. over 10-20 farads, that is..

For your specific question... cap should be grounded to the same central point as all the amps. Whether that is a ground block or a bolt to the chassis. Don't depend on the Cap as your primary ground. I guess if the cap has a Dist block on it... ground everything to the block & then an equivilent ga wire to your main power wire to the chassis.

Rob


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## elvisjer (May 13, 2008)

THe only reason im running the cap is because i had one spare, 2 farad, and the distro block is nice and was $7. Im not relying on the cap to have any benefits. So would it be better to ground things directly to the chassis or the cap?


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## [email protected] (Jun 12, 2008)

either way, dont think one would be better than the other, I see alot of grounding to the cap the cap to chassis


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## ChrisB (Jul 3, 2008)

I have two positive things to say about caps:
1. I used a cap back in 1998 to cure a noise problem that no one could solve. I used it purely as a filtering device and it actually worked, to my surprise, quite well!

2. Some of the newer ones have voltage meters.

3. If you already have one, why not use it?

Sadly, most capacitors DO NOT perform in the way that they are marketed. In fact, they usually do more harm than good because your charging system will have to provide current to charge the cap and keep the music running.

Another negative thing about them is that they can and WILL explode if directly shorted. I saw pictures of the aftermath of one blowing, and it left a three to four foot arc in the trunk. I am real good friends with the installer who was trying to fix that "self-install" and he is thankful that nothing happened to him when the capacitor blew up away from his face instead of towards it. Had it blown the other way, he would either be blind or dead!


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## Oliver (Jun 25, 2007)

Ground directly to a point on the vehicle [not to the capacitor ]

info:A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.Like a Water Tower
One way to visualize the action of a capacitor is to imagine it as a water tower hooked to a pipe. A water tower "stores" water pressure -- when the water system pumps produce more water than a town needs, the excess is stored in the water tower. Then, at times of high demand, the excess water flows out of the tower to keep the pressure up. A capacitor stores electrons in the same way and can then release them later.



http://electronics.howstuffworks.com/capacitor.htm

alot of things can hurt you {if you don't understand them}
in reference to this: Another negative thing about them is that they can and WILL explode if directly shorted.


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## elvisjer (May 13, 2008)

Agh im not trying to debate about whether capacitors are needed or not lol, there's enough of those threads all over the place already  Well now im getting some people say ground to the cap, and some to the chassis....is there an advantage of grounding to the cap?


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## ChrisB (Jul 3, 2008)

I just like to re-iterate the fact that capacitors have the potential to be dangerous if not handled properly. Many of the cap manufacturers say that caps won't explode, but instead will leak out their electrolytic fluid if directly shorted. Heck, I have seen my share of fried circuit boards where those tiny capacitors pop like firecrackers. 

The easy solution is to say "Well don't directly short it". Unfortunately, in the event of a car accident, no one knows what will happen to a cap that is connected to the audio system.....


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## elvisjer (May 13, 2008)

I like to live on the dangerous side.    Thanks for the info actually, its a good thing to know. Im sure Volvos have capacitor airbags now somewhere


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## [email protected] (Jun 12, 2008)

elvisjer said:


> I like to live on the dangerous side.    Thanks for the info actually, its a good thing to know. Im sure Volvos have capacitor airbags now somewhere


I have installed quite a few caps in my days, I always grounded to the cap and used the cap a a grounding block coming off the cap with 1/0 guage wire to the chasis of the car, my buddy has had his installed that way for 4+ years and not a single issue, I have 3 amps wire to it, 1 4ch and 2 small monos, its like a 5 farad cap i think


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## Oliver (Jun 25, 2007)

A load in electricity is something that "does work", speakers , headlights, motors , amps, etc..,

A capacitor is a "storage device" , plain an simple

In reference to this info:... A cap is no different to the alternator than another amp, processor, battery or fancy blinking lights... its a load.


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## elvisjer (May 13, 2008)

Awesome thanks for the help all!


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## MarkZ (Dec 5, 2005)

06BLMUSTANGGT said:


> I just like to re-iterate the fact that capacitors have the potential to be dangerous if not handled properly. Many of the cap manufacturers say that caps won't explode, but instead will leak out their electrolytic fluid if directly shorted. Heck, I have seen my share of fried circuit boards where those tiny capacitors pop like firecrackers.
> 
> The easy solution is to say "Well don't directly short it". Unfortunately, in the event of a car accident, no one knows what will happen to a cap that is connected to the audio system.....


That's a good point. They'll also do funny things if there's an overvoltage condition.

They should be installed under the hood. If there's no room, then in the trunk if it's sealed off from the cabin. Or under the backseat, if that's where your battery is.


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## exmaxima1 (May 31, 2007)

a$$hole said:


> alot of things can hurt you {if you don't understand them}
> in reference to this: Another negative thing about them is that they can and WILL explode if directly shorted.
> 
> 
> ...


You are incorrect on both points:

1. A charged cap should not explode if directly shorted. The instantaneous discharge through the leads may result in sparks and possibly heating of the leads, but any cap designed for automotive audio use will certainly handle the discharge without failure. For example, Alumapro's The C.A.P. has been tested to over ONE MILLION full charge/dead short cycles without failure.

2. A load must draw current to be a load, and VxI=Power. Once a cap is charged, typically in less than a second in an automotive application, it draws essentially zero additional current, so it cannot possibly be a "load". When something draws energy off the cap, such as an amplifier, the cap must be refilled but nothing is lost (it is typically over 99% efficient). In contrast, a battery draws significant current in the charging process and can be considered a load on the alternator (lead-acid batteries may be as little as 5% efficient in converting current to stored energy). Even when fully charged, a battery will still draw a few amps of current. Using multiple batteries multiplies the current drain on the alternator. Caps are therefore much more desirable when you must consider efficiency and charge rates.


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## exmaxima1 (May 31, 2007)

MarkZ said:


> That's a good point. They'll also do funny things if there's an overvoltage condition.
> 
> They should be installed under the hood. If there's no room, then in the trunk if it's sealed off from the cabin. Or under the backseat, if that's where your battery is.



Caps, like most electronic components, degrade from heat. Under the hood in the engine compartment is the LAST place to locate a capacitor.

The appropriate place to install a capacitor is as close as possible to the amplifiers. Ideally the leads to the amplifier should be less than 16 inches to minimize inductance (which limits cycle speed).


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## ChrisB (Jul 3, 2008)

exmaxima1 said:


> You are incorrect on both points:
> 
> 1. A charged cap should not explode if directly shorted. The instantaneous discharge through the leads may result in sparks and possibly heating of the leads, but any cap designed for automotive audio use will certainly handle the discharge without failure. For example, Alumapro's The C.A.P. has been tested to over ONE MILLION full charge/dead short cycles without failure.


I'll make sure I convey your message to my friend Nick who could have been seriously injured or killed by the exploding capacitor that left a three to four foot arc in the trunk of the car after it exploded!


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## chad (Jun 30, 2005)

exmaxima1 said:


> You are incorrect on both points:
> 
> 1. A charged cap should not explode if directly shorted. The instantaneous discharge through the leads may result in sparks and possibly heating of the leads, but any cap designed for automotive audio use will certainly handle the discharge without failure. For example, Alumapro's The C.A.P. has been tested to over ONE MILLION full charge/dead short cycles without failure.


I would like to add that THIS IS ONE OF THE PURPOSES OF A CAP! to provide HUGE instantaneous current, a cap does not know if it's supplying said current to a dead short or your sub amp making mad dee-beez, or your starter motor (since it's in parallel  )



06BLMUSTANGGT said:


> I'll make sure I convey your message to my friend Nick who could have been seriously injured or killed by the exploding capacitor that left a three to four foot arc in the trunk of the car after it exploded!



A it was not a cap but rather a battery called a cap like the [shudder] battcap

-or- 

B it was a faulty/damaged capacitor. I have seen caps blow up too, but it was physically damaged first, operated in a state it was not designed for, or was old enough to not take the heat anymore in which it's failure was unrelated to developing current as in a short situation. You sure it was hooked up correctly in regards to polarity?


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## ChrisB (Jul 3, 2008)

chad said:


> A it was not a cap but rather a battery called a cap like the [shudder] battcap
> 
> -or-
> 
> B it was a faulty/damaged capacitor. I have seen caps blow up too, but it was physically damaged first, operated in a state it was not designed for, or was old enough to not take the heat anymore in which it's failure was unrelated to developing current as in a short situation. You sure it was hooked up correctly in regards to polarity?


From the pictures I saw of the aftermath, I would be willing to bet that it was hooked up with reversed polarity and possibly charged @ 24 volts because I couldn't make heads or tails of that DIY dude's craptastic wiring from the photos. Regardless, my friend Nick has developed post traumatic stress disorder due to caps and he still will not recommend them!

ETA: The cap that blew up was just the standard, run of the mill 1 farad capacitor that you could get in 1999/2000.


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## SSSnake (Mar 8, 2007)

Actually a cap does know the difference between a dead short and an amp or starter... An amp or starter has resistance and therefore the current draw is fairly limited in comparison to a dead short. The only resistance in an ideal dead short (which is seldom encountered) is the ESR of the cap. Disapating all of the power across the ESR of the cap causes lots of heat to be built up in the cap. With those cheap 1F jobs that kept showing up in the mid nineties this can and has led to some nasty explosions.


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## chad (Jun 30, 2005)

06BLMUSTANGGT said:


> Regardless, my friend Nick has developed post traumatic stress disorder due to caps and he still will not recommend them!


I don't know if you meant it to be, but that was straight up funny to me 



SSSnake said:


> Actually a cap does know the difference between a dead short and an amp or starter... An amp or starter has resistance and therefore the current draw is fairly limited in comparison to a dead short. The only resistance in an ideal dead short (which is seldom encountered) is the ESR of the cap. Disapating all of the power across the ESR of the cap causes lots of heat to be built up in the cap. With those cheap 1F jobs that kept showing up in the mid nineties this can and has led to some nasty explosions.



Oh come now, have we never heard of inrush or even worse the back EMF coming off of that starter when it's disengaged? You know the things that happen to caps over and over when used in an automotive application? A cap sees an over-voltage condition all the time and nearly a dead short all the time when a car is started, don't believe me on the over voltage? Put your fingers across the cap, go ahead it's only 12V, while your fingers are there have a friend tick that starter and tell me how fast you get your hand off of it  Starting systems work as excellent de-sulficators for lead acid batteries  I would also recommend measuring the static resistance of a starter, especially old skool, non-gear reduced, it's pretty damn low. probably lower than that of the common device that will short a cap after heating.

That being said, along with my most recent post, a cap made in the mid 90's and used in a car in a climate that has a good summer is probably nearing the end of it's useful life due to heat, vibration, and possible physical damage.


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## ChrisB (Jul 3, 2008)

chad said:


> I don't know if you meant it to be, but that was straight up funny to me


He jokes about it now saying how he had to go home, shower, and change his underwear before he could finish un-fking that guy's ghetto fabulous install!


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## MarkZ (Dec 5, 2005)

exmaxima1 said:


> Caps, like most electronic components, degrade from heat. Under the hood in the engine compartment is the LAST place to locate a capacitor.
> 
> The appropriate place to install a capacitor is as close as possible to the amplifiers. Ideally the leads to the amplifier should be less than 16 inches to minimize inductance (which limits cycle speed).


Amplifiers don't need caps. Headlights do. They should be installed as close (electrically) to the headlights as possible. Next to the battery is a great spot.

And yes, I recognize that in some cars, under the hood isn't feasible. But not because of the heat issue. Most should be able to withstand those temperatures, unless you're bolting it to the block.


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## chad (Jun 30, 2005)

06BLMUSTANGGT said:


> He jokes about it now saying how he had to go home, shower, and change his underwear before he could finish un-fking that guy's ghetto fabulous install!


I was rebuilding on a QSC1400 that was in BAD shape, sometimes I'll leave the finals out and bring it up slow to probe around so I don't munch a rack of expensive finals  Everything LOOKED OK till it took off into oscillation (still don't know why) and the bank of filter caps went off like firecrackers. I screamed like a little girl.

There is still a can from a filter cap embedded in my parent's garage ceiling from when I built my first amp as a youngster and placed a filter cap in backwards. They won't let me remove it, but they sure remind me of it on a regular basis


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## Oliver (Jun 25, 2007)

Pics Chad !


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## exmaxima1 (May 31, 2007)

MarkZ said:


> Amplifiers don't need caps. Headlights do. They should be installed as close (electrically) to the headlights as possible. Next to the battery is a great spot.


I guess that it like saying the answer to gun control is to issue bullet-proof vests to everyone, instead of stopping the shooting at the source  

The reason the lights are dimming is that the amplifiers are demanding high peak currents and the draw is bringing down the electrical system voltage. If you address the headlights directly, you still have large voltage swings affecting other parts of the system such as radio/processors/computer. Mainly everything near the amplifiers. If, instead, you install the appropriately sized cap close to the amplifiers, the total system voltage will remain more stable and with less voltage fluctuation.

Also, while a cap should be fine if kept from direct engine heat, long-term elevated temps under the hood will still reduce the useful life of the device. Conversely, some caps may also be damaged by freezing temps in the airflow under the hood. It's just plain good practice to keep them away from wide temp extremes.


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## Oliver (Jun 25, 2007)

Quote>
It's just plain good practice to keep them away from wide temp extremes.
quote>

keep them in the stores !!


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## MarkZ (Dec 5, 2005)

exmaxima1 said:


> I guess that it like saying the answer to gun control is to issue bullet-proof vests to everyone, instead of stopping the shooting at the source
> 
> The reason the lights are dimming is that the amplifiers are demanding high peak currents and the draw is bringing down the electrical system voltage. If you address the headlights directly, you still have large voltage swings affecting other parts of the system such as radio/processors/computer. Mainly everything near the amplifiers. If, instead, you install the appropriately sized cap close to the amplifiers, the total system voltage will remain more stable and with less voltage fluctuation.


I agree. But the fluctuations in the electrical system don't really matter, except where they noticably manifest themselves: light dimming. There are a number of ways to address light dimming, of course, but if a capacitor is one of them -- it will most effectively reduce dimming by minimizing the series impedance to the lights themselves, not to the load that's drawing the most current (in this case, the amp).

In other words, installing it electrically close to the amps will minimize the fluctuation at the amps, but installing it electrically close to the rest of the electrical system will minimize the fluctuation to the rest of the electrical system.

Although, having said that, it's probably not that big of a difference where you put it. These are relatively low impedances we're talking about, especially if people are using big wires. Sometimes people want to show off capacitors too for some reason, so they may have a better spot for them. My only point is that you shouldn't let the old adage "cap near the amp" dictate where you install it, and I also don't believe it should be installed in the cabin (like if the amp is installed under the front seat...).

Maybe chad will remember this, but I thought on usenet a while back a guy claimed that his cap "exploded" and he had it mounted under the seat. I forget exactly how it went, but I think it was a rec.audio.car post...



> Also, while a cap should be fine if kept from direct engine heat, long-term elevated temps under the hood will still reduce the useful life of the device. Conversely, some caps may also be damaged by freezing temps in the airflow under the hood. It's just plain good practice to keep them away from wide temp extremes.


You might be right. I never considered them to be TOO extreme for caps though, although in some cars and some locations under the hood I could see that. 

But I wonder if there's any circuitry already under the hood that may have electrolytics in them? My last car had a remote start brain (of some sort) on the firewall. Those caps would be subjected to the same kinds of temperature extremes you're talking about. Maybe the bigger ones are more sensitive?, but I would think the opposite would be true...


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## exmaxima1 (May 31, 2007)

chad said:


> There is still a can from a filter cap embedded in my parent's garage ceiling from when I built my first amp as a youngster and placed a filter cap in backwards. They won't let me remove it, but they sure remind me of it on a regular basis


That's funny! My parents' garage still has a hole from a match cannon I shot 40 years ago---and they never knew about it!


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## exmaxima1 (May 31, 2007)

a$$hole said:


> Quote>
> It's just plain good practice to keep them away from wide temp extremes.
> quote>
> 
> keep them in the stores !!


Well, without power capacitors you wouldn't have:

1. Kinetic watches---they charge a cap to keep running

2. Satellites---pretty hard to service batteries in orbit, while caps last for many years. Solar cells only work when they in the presence of sunlight.

3. Disney rides---some use caps for their trackless people movers

4. Low-cost distributed accessory power for locks/windows---newer vehicles have a multitude of caps in the doors to alleviate the need for expensive/heavy copper wiring.

5. High-tech plasma guns---the future depends on advanced capacitor technology!


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## Hispls (Mar 12, 2008)

I used to blow up the little firecracker size caps for fun. One of those bling bling ones must go off like a half stick of dynamite!


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## elvisjer (May 13, 2008)

Wow, this thread would be nearly empty if people were talking only about the original subject


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## MarkZ (Dec 5, 2005)

elvisjer said:


> Wow, this thread would be nearly empty if people were talking only about the original subject


HAhaha...welcome to the magical world of DIYMA! I'm king of the sidetracked conversation.


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## SSSnake (Mar 8, 2007)

> nearly a dead short all the time


 <> dead short

Back to the original subject...

All high current paths (power and ground) should have as few connection points as possible to maximize usable voltage. This DOES NOT mean I am a proponent of no fuses or anything crazy like that. However, unless you know the cap is benefitting the system then I would not use it much less include it in the ground path.


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## TXwrxWagon (Sep 26, 2008)

a$$hole said:


> A load in electricity is something that "does work", speakers , headlights, motors , amps, etc..,
> 
> A capacitor is a "storage device" , plain an simple
> 
> In reference to this info:... A cap is no different to the alternator than another amp, processor, battery or fancy blinking lights... its a load.


Sorry... incorrect... if it needs to be "charged" it is a LOAD to the alternator. If the cap, as you stated cannot create electrons... then the electrons have to come from somewhere & when that peak need is reached, the cap has to be recharged. Plain & simple... Your bank account doesn't grow money, you make deposits. Same thing. If your account is low on funds its a DRAW.. its a load. 

Anything that is connected to the electrical system is a load. I agree that the cap can be a "storage device" until called upon. A battery is a storage device as well. But in order to store it has to be charged...

Rob


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## MarkZ (Dec 5, 2005)

TXwrxWagon said:


> Sorry... incorrect... if it needs to be "charged" it is a LOAD to the alternator. If the cap, as you stated cannot create electrons... then the electrons have to come from somewhere & when that peak need is reached, the cap has to be recharged. Plain & simple...


When does the cap recharge?

It (basically) recharges when the peak demands END. So, if it's an additional load, it's only a transient one. And so the load is maximal when the electrical system is doing nothing else.

As a result, the "load" the cap presents to the electrical system is inconsequential.


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## TXwrxWagon (Sep 26, 2008)

the application of Cap's in the car audio environment is a LOAD. Inconsequential or not,its a load... and the way they are marketed, as a band-aid for dimming lights & other electrical system maladies makes them an even greater load on the electrical system.

But I guess Richard Clark & all the other "experts" in our hobby are all stupid...

a capacitor in the role of a storage device, in a car audio is a joke... Unless you have 10+ farads of storage & everything in your electrical is completely in check.

The transient response rate of any given amplifier (aka slew rate) is a given. A cap is a band-aid... yes it may work temporarily, but it is a band-aid & a load.

Rob


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## MarkZ (Dec 5, 2005)

TXwrxWagon said:


> the application of Cap's in the car audio environment is a LOAD. Inconsequential or not,its a load... and the way they are marketed, as a band-aid for dimming lights & other electrical system maladies makes them an even greater load on the electrical system.
> 
> But I guess Richard Clark & all the other "experts" in our hobby are all stupid...
> 
> ...


See, you just admitted it may work. 

I don't really disagree with your take on it. I just think there are numerous cases where it reduces or even eliminates dimming. There might be better ways of achieving the same thing, but sometimes adding a cap is the easiest and cheapest. Especially for the folks who already have a cap sitting around.


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## TXwrxWagon (Sep 26, 2008)

I never said it DID NOT work I said & have always told my customers it is BAND AID... 

As I said to the original poster: If you've got it, or at $7 "to test it what the hell" I would too... but the bottom line is that the cap is a LOAD & it is a band aid/Marketing Hy[e-Fix to get people's money.

Otherwise we would see every single top IASCA & USACi competitor in the top classes running them. They don't... I admit I like to get my hair cut from a sexy, buxom babe @ the local shop... NOT because she gives me a BETTER hair cut... .. LOL

Rob


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## MarkZ (Dec 5, 2005)

TXwrxWagon said:


> I never said it DID NOT work I said & have always told my customers it is BAND AID...
> 
> As I said to the original poster: If you've got it, or at $7 "to test it what the hell" I would too... but the bottom line is that the cap is a LOAD & it is a band aid/Marketing Hy[e-Fix to get people's money.
> 
> ...


See? There's something to be said for band-aids...


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## TXwrxWagon (Sep 26, 2008)

yep band-aids can hold your finger in place on your way to the emergency room to have the digit reatched when you cut it off with the table saw....



Rob


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## TXwrxWagon (Sep 26, 2008)

MarkZ said:


> Amplifiers don't need caps. Headlights do. They should be installed as close (electrically) to the headlights as possible. Next to the battery is a great spot.
> 
> And yes, I recognize that in some cars, under the hood isn't feasible. But not because of the heat issue. Most should be able to withstand those temperatures, unless you're bolting it to the block.



I was re-reading this entire thread & I have to just say WTF!? HEADLIGHTS need caps?

No, the electrical system needs to be up to the task of supplying the LOAD of all the various components in the car.... 

If the car itself draws , say 45 amps of current (AC, headlights, accessories etc) then you add a 100amp draw from a stereo, you need 145 amps of current from the alternator. You do understand that the car runs on the ALTERNATOR not the battery, right? The battery IS a true storage device. its sole purpose is to START the car. Nothing else.The alternator provides ALL power for the car & its accessories.

There are VERY few cars/SUV's with an OE 145 amp alternator. So putting a Cap anywhere in the car is like adding another amp, a set of fog lights or a neon underbody kit... its a LOAD... it needs to be supported by the electrical source.

Putting the cap near the headlights... OMG! that is the best one I have heard in YEARS

Rob


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## MarkZ (Dec 5, 2005)

TXwrxWagon said:


> I was re-reading this entire thread & I have to just say WTF!? HEADLIGHTS need caps?
> 
> No, the electrical system needs to be up to the task of supplying the LOAD of all the various components in the car....


Yep. And, with very few exceptions, it does that successfully no matter what amps you hook up to them. So why do people upgrade their electrical systems? It's not like the amps are shutting off mid-beat. Or that the car is stalling. It's almost always because the HEADLIGHTS (or interior lights) are dimming with the bass. The goal, then, is to reduce the headlight dimming. There's no other goal.

Therefore, to address that goal, the best approach is to reduce the voltage fluctuations present at the headlight terminals. The ideal way to do that would be to diode isolate them, place parallel capacitors (and even series inductors!) in the circuit, and letting the headlight switch drive a relay. But that's a *****. The easier way is to put a big honkin' capacitor in the electrical system, as electrically close to the headlights as possible.



> If the car itself draws , say 45 amps of current (AC, headlights, accessories etc) then you add a 100amp draw from a stereo, you need 145 amps of current from the alternator. You do understand that the car runs on the ALTERNATOR not the battery, right? The battery IS a true storage device. its sole purpose is to START the car. Nothing else.The alternator provides ALL power for the car & its accessories.


Spoken like someone who's never inadvertently had their batter cable become disconnected with the car running.  I won't advise that you do that, because it's not generally a good thing. But if you did, you'd find that the alternator is incapable of sustaining its voltage during peak demands. What happens (at least most of the time) is that the voltage dips so low when the bass hits that the amplifier shuts off. 

Contrary to popular belief, the battery is SUPPLYING current during peak demands, especially when the RPMs are below the alternator's peak efficiency!



> There are VERY few cars/SUV's with an OE 145 amp alternator. So putting a Cap anywhere in the car is like adding another amp, a set of fog lights or a neon underbody kit... its a LOAD... it needs to be supported by the electrical source.


This isn't true, and I explained why in an earlier post. When the capacitor is recharging (thus appearing as a "load" to the electrical system), it's NOT during peak demand. It's in between transients. So the electrical system is really not doing anything else during that time. During peak demand, the voltage is at its lowest point and is in fact equal to the capacitor voltage (otherwise, the capacitor would still be DISCHARGING). Therefore, ohm's law dictates that it won't be charging at that time. It isn't until the electrical system's voltage rebounds that the capacitor can begin to draw current from it again.



> Putting the cap near the headlights... OMG! that is the best one I have heard in YEARS


Thanks. I think?


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## TXwrxWagon (Sep 26, 2008)

not a shot at you at all... we just see the electrical load & system requirements of the vehicle differently. 

My stance is that if the charging system, system wiring, & a quality battery, all coupled with sound installation techniques, there should never be a need supplementation. 

Even in the biggest of SPL vehicles, they use the caps from their sponsors, not that they need them, they run more batteries than many can carry on the street, the vehicles don't need to start or even drive. & those that do have 2 dedicated electrical systems & outboard 110v/220v power supplies keeping the batteries charged for that, I don't even remember the cycle burst time now, I don't keep up with SPL contests/rules anymore. 

Its all good.. 

Rob


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## MarkZ (Dec 5, 2005)

I mostly agree. But I would contend that it's often easier and cost-effective to add a cap than it is to upgrade the battery an alternator. And if it works, why not?


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## chad (Jun 30, 2005)

MarkZ said:


> I mostly agree. But I would contend that it's often easier and cost-effective to add a cap than it is to upgrade the battery an alternator. And if it works, why not?


Because the expense of a QUALITY cap LARGE enough to be effective would equate to or be more than a damn fine battery that will simply solve the issue at hand.


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## exmaxima1 (May 31, 2007)

chad said:


> Because the expense of a QUALITY cap LARGE enough to be effective would equate to or be more than a damn fine battery that will simply solve the issue at hand.


That reminded me of a cap we made for those jumping cars with the hydraulic suspensions. It is rated for 72 volts and 30 kJ (30,000 Joules). You hook this up to a 12 volt pump, and the car leaps into the air!

It was engineered specifically for this application and replaces (6) full-size lead acid batteries. In tests, voltage drooped to only 60 volts using the cap, while the battery pack would droop to 48 volts. In addition, it weighs at least 200 lbs less.

But the problem was cost---the cap would cost about $1500, and the necessary DC-DC converter to generate the 72 volts was pretty expensive as well. Even though it would win contests, and probably last forever, that industry prefers the K-Mart mentality.

One more point: the reason you don't see many caps in audio competition is that the big boys outlawed multi-farad caps. Guys like your hero, Richard Clark, had a financial interest in the 1F electrolytic cans and re-wrote the rules to push out a technology that would limit their sales. But before the rules changed, you would find many CAP15 and CAP5 devices in competition.


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## elvisjer (May 13, 2008)

Note to self, never mention caps in a thread ever again


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## less (Nov 30, 2006)

Haha,

I love this whole topic since there just is no universally agreed upon opinion... its great! Lets see if I can add to the entertainment value of this though...

30 years ago when I was in high school, I had an electronics class. Mr. DeGrow was the teacher and he was my favorite teacher ever... had a great sense of humor! He taught us stuff like the resistor color code: Bad Boys Rape Our Young Girls But Violet Gives Willingly! (At 16 that was pretty funny in the 70s!)

Well we were blessed to have Dow Chemical company to have been gifted huge numbers of old electrical components to tear apart and rebuild into things we could think of that might be useful. One of the parts we ran across on a regular basis was... old 1/2 farad capacitors! Weee... they make great toys! We would charge them up with a hand crank generator and short them out for fun.

The very first time one actually was shorted though was hilarious! There was a kid in the class after us that was just a goober! He'd come into our class early at times and just grab whatever and start messing with it. Mr. DeGrow charged up one of the biggest caps we'd ever seen and set it on the counter at the front of the class... then he told us all, "Watch, Danny is going to come in here and pick it up and start to play with it... I am going to tell him to lick the two poles!"

I couldn't believe it! Literally, thats exactly what happened. Danny came in immediately picked it up and started to swing it around and play with it... DeGrow says... stick your tongue on it... Danny takes the thing and moves it toward his mouth and you could literally hear the intake of breath from everyone in the room... We all just sat there staring at him... waiting! He stuck his tongue out and kept it out for what seemed like minutes... all the time looking at us.

Suddenly, its like a lightbulb went off and he put it down and said... "you guys are all acting like this thing will hurt me but no way!" He then tapped the two terminals across a stainless steel faucet spout that was sticking up off the desk. 

The sound was amazing..... ZZZZZzzzzwwwaaapppppp! Sparks flew everywhere and Danny screamed like a girl. The look in his eyes was the best thing ever.... shocked, pissed, scared to death and unbelieving all at once. After that we slid two or three of the charged caps into metal trash cans where they nearly tore through the sides of these thick metal cans and left dents at least 1/4" deep as well as black scars roughly 5 inches around in a circle where they hit.

To do this story justice, I should add that Danny passed away the very next year. Poor Danny really was a kid who would try anything and one day his parents came home to find him with his nose literally impaled on the edge of a one gallon gas can in the garage. I always felt bad about not just telling Danny not to do it... because at one point I was 100% convinced he was going to do it... needless to say, he'd have lost his tongue and probably teeth and lips as well.

Life is strange at times...

Less


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## less (Nov 30, 2006)

Now that the story is complete, I'd like to raise a point for discussion or explanation. I've worked with electronics all my life but never had any real education besides that one electronics class - and that wasn't really a very good class if you honestly wanted to learn. So, my knowledge is sometimes great and indepth through personal study, but other times not so hot... so I rely on others. (I am referring to more advanced topics here - not basics at all... I've got those down=)

So, here it is: All amplifiers use a lot of capacitors in their power supply circuits... although for some reason it appears that home amplifiers tend to use much more massive capacitors then car amps. The reason for these capacitors seems to be to assure that there is always ample power available when the amp is asked to output high levels on peaks, to assure that the amp is able to continuously output quality sound... leaving no gaps in output or no degradation in output.

I've played out this whole capacitor discussion doing my best to understand both sides, but in the end, I always come back to the thought that every amp uses these in their power supplies for just about the same reason as why people want to put them in their power system - to fill the holes that occur during musical / electrical peak draw periods. 

I hear that they are a load... when it occurs to me that they don't use hardly any energy (except what is lost in conversion to heat) and instead aid the electrical system and all the electronic parts in the vehicle by allowing them to have a more constant and smooth supply of the power they all run off. This would seem to make them very useful in keeping things like your ECU and other electronic equipment in todays cars and assist them in their durability and stability.

I also read someones huge long demonstration the other day that adding a second battery is a load on the alternator - with the conclusion being that they are not good for the system. Well hell! I bought a second battery - one of the newer Stingers that discharge more quickly etc. I did this knowing full well that it would constantly be asking the generating system for power... but also that it would store much of that power and feed the entire system with power when the alternator can't keep up! The battery has to represent a load ... but (even though they are apparently not as efficient as a cap) they don't use the power they ask for... they store it and release it later when its needed!

I'd like an explanation of why the caps inside the amp are useful but ones outside the amp but feeding it aren't please. I've read plenty and even been convinced at one point that caps truly were useless... but no one has explained it in these terms that would help me feel more comfortable about this whole deal.

If someone wants to chime in on the battery comment I through in - feel free to do that too!

Sorry about the questions inside anothers post... but lets face it - this thread is way off the original point anyhow =)

Less


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## starboy869 (Dec 16, 2006)

less said:


> I'd like an explanation of why the caps inside the amp are useful but ones outside the amp but feeding it aren't please. I've read plenty and even been convinced at one point that caps truly were useless... but no one has explained it in these terms that would help me feel more comfortable about this whole deal.
> 
> Less


The internet bandwagon forgot about this


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## SSSnake (Mar 8, 2007)

Less,

A couple of thoughts...

The main culprit with caps is ESR. ESR can rob a cap of its usefullness. Why? ESR causes voltage and power to be lost as heat within the cap. Why would this NOT be the case in the amp and especially in home amps where large caps in the power supply are the norm (for high end amps). It is all a question of voltage... 

My guess (and someone who is familiar with amp power supply design please correct me - I have forgotten more than I care to admit) is that the caps are in a high voltage section of the power supply. In a high voltage section current is much lower therefore the voltage lost and power lost is much lower (power lost = current^2 * ESR or voltage^2 / ESR). If the voltage is 120V vs 12V then the power lost drops by a factor of 100.

It is pretty easy to see placing caps in higher voltage and lower current sections can yield some large gains in efficiency. But what does that mean in a car audio application where the additional caps are on the outside of the amp? IF ESR is too large the power storage provided the capacitor is quickly consumed within the cap itself providing minimal benifit. If ESR is low enough then the cap will porivde additional power to the amp to support transients. Why do some people believe that having a ton of 1F caps is better than a big 100F cap. Well capacitance adds in parallel but resistance decreases in parallel. Therefore a bundle of 100 1F capacitors will give you 100F and and ESR that is 1/100th of the single cap. But here's the catch... You have to connect all of those stinking caps together an all connections add resistance. Therefore the equivalent ESR for a bundle of caps can and typically is much greater than the ESR/100.

What does all of this mean to me... IMO - commercially available audio marketed caps, external to the amp, are typically more trouble than they are worth. If you really are set on adding caps check out "Boost Caps". They are used in some high current electrical motor applications and have been pretty effective. 


And I end this long winded response by saying all of this is IN MY OPINION. If you don't like it well... it is worth what you paid for it.


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## chad (Jun 30, 2005)

elvisjer said:


> Note to self, never mention caps in a thread ever again


LOL! That's sig worthy!


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## Oliver (Jun 25, 2007)

Great amps actually don't need what is already inside them, low priced amps are designed with minimal reserves of power [ headlights going with the music ], battery dies, alternator dies, etc..,


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## TXwrxWagon (Sep 26, 2008)

Damn I wish I could find that original Tech Brief from Autosound 2000 online to link too... I just don't want to type up 15 pages of stuff from the paper brief & link to it...

The story of the kid touching his tongue to the cap made me shoot my beer across the room through my nose... THAT was funny!

ESR is indeed the primary issue which relates to the REAL cost of building USEABLE & FUNCTIONAL caps for the use we intend here.

Thanks, to whomever, for the correction on the SPL rules outlawing the caps. Alumapro "semi-serious" caps are the only caps I have sold with out feeling I am raping a customer of their hard earned $$.. & then I still qualified them very VERy carefully to be sure they needed it at all.

The trick in the mobile audio market place is that accessories/add-on's = higher commission levels & usually spiffs & perks to selling them. So the push is for the "add-on".. For the most part, its a marketing game.

But, as I said in my very first post.. $7.. why not try it.. if it works for ya... GREAT 3 pages of back-n-forth out the window... LOL

Rob


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## elvisjer (May 13, 2008)

Hey, if it's sig worthy id be honored


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## sqshoestring (Jun 19, 2007)

Amount of capacitance in an amp is not really related to its quality. I see more in cheaper amps but sometimes the opposite. There should be more if the power supply is noisy, as they are there more to do that than hold power. I have a newer alpine with hardly any cap in it compared to other similar size amps, yet they are not considered a junk amp. Some high power amps do put a bunch of caps in there, or use a lot of smaller ones. I've been told it has more to do with how good/powerful the power supply is, also been told the rails are where you want to add more cap not 12v before the power supply. Yet I've had someone who designed amps say a good amp should not benefit from any of that, and he meant good not best...meaning most amps should not need any more capacitance anywhere. However he did think a big cap could help the electrical system of the car by smoothing voltage spikes. Said anything in your car electrical/electronic is seeing them.


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## elvisjer (May 13, 2008)

Is there anyway i can press a button to make everyone stop and consider whether they are helping with my original problem and if not, they must punch themselves in the face? That would be cool. Somebody is going to be having the same question as me initially and see a 3+ page thread and get very excited, open it, and then go kill themselves


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## MarkZ (Dec 5, 2005)

SSSnake said:


> My guess (and someone who is familiar with amp power supply design please correct me - I have forgotten more than I care to admit) is that the caps are in a high voltage section of the power supply. In a high voltage section current is much lower therefore the voltage lost and power lost is much lower (power lost = current^2 * ESR or voltage^2 / ESR). If the voltage is 120V vs 12V then the power lost drops by a factor of 100.


There are caps on the rails, but that's not what we're talking about here. The type of cap that's being discussed here is on the 12v section.

But you bring up an interesting point. Maybe we should be beefing up the caps after the transformer instead? 

I'd like to just reiterate that the role of the caps we're talking about ISN'T to help the amp. It won't make it sound better, live longer, etc [yeah, I know some of you will disagree...]. People generally install caps in an attempt to reduce headlight and interior light dimming. I think it's useful to always keep this in mind while discussing the issue.



elvisjer said:


> Is there anyway i can press a button to make everyone stop and consider whether they are helping with my original problem and if not, they must punch themselves in the face? That would be cool. Somebody is going to be having the same question as me initially and see a 3+ page thread and get very excited, open it, and then go kill themselves


Nah, we're having fun.  Seriously, though, I think getting sidetracked sometimes leads to some interesting observations, stories, and debates. Didn't you already get an answer to your grounding question though?


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