Cap or not to cap, capacitor
#1
11-03-2010, 01:33 PM
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Cap or not to cap, capacitor
So everyone says Capacitors are not needed (as I recently found out).
After revising my Electrical 101, here is my rant.
Capacitor will protect factory alternators.
Every time the amp wants more current, the battery and alternator will see a drop in resistance on the entire 12V bus on your vehicle. If the battery is unable to provide that current, your alternator will try to. This means that your alternator will have peaks of higher current running at those times.
Heat generated is a squared function of current, meaning if your alternator is providing 1A constant, instead of peaks of 0.6A --> 1.4A, the 1.4A peaks will generate more heat in bursts within the coil. This will in no doubt shorten the life of your alternator.
Now if you put in a Capacitor, the current bursts that were being provided by your alternator will be shared with the capacitor, your alternator will have load spread over time.
Given the choice, I would generate less current over a long period as the function for heat generated is ((I^2)*r*t), where I is the current, so if current goes up, more heat is generated as current is squared, time on the other hand is not squared.
So IMO, if you feel you are gonna strain the alternator, put in a capacitor.
If you got a huge alternator, skip it.
Please let me know of gaps in my analysis.
After revising my Electrical 101, here is my rant.
Capacitor will protect factory alternators.
Every time the amp wants more current, the battery and alternator will see a drop in resistance on the entire 12V bus on your vehicle. If the battery is unable to provide that current, your alternator will try to. This means that your alternator will have peaks of higher current running at those times.
Heat generated is a squared function of current, meaning if your alternator is providing 1A constant, instead of peaks of 0.6A --> 1.4A, the 1.4A peaks will generate more heat in bursts within the coil. This will in no doubt shorten the life of your alternator.
Now if you put in a Capacitor, the current bursts that were being provided by your alternator will be shared with the capacitor, your alternator will have load spread over time.
Given the choice, I would generate less current over a long period as the function for heat generated is ((I^2)*r*t), where I is the current, so if current goes up, more heat is generated as current is squared, time on the other hand is not squared.
So IMO, if you feel you are gonna strain the alternator, put in a capacitor.
If you got a huge alternator, skip it.
Please let me know of gaps in my analysis.
#2
11-03-2010, 03:19 PM
#3
11-03-2010, 05:34 PM
The analogy of a glass of water would be true if your battery was disconnected suddenly, and the capacitor completely discharged, but the capacitor can only discharge whatever % of the charge it has over what the charging system is currently at. If your charging system is at 14 volts, then a pull of music takes it down to 12 volts, you'll only pull 2 volts out of the capacitor (1/7th of it's total capacity). If you have a sustained bass note at all, you drain that capacitor nearly instantly (remember all their advertising about "instant power?" yeah, instantly gone. Once that tiny reserve above the charging system's voltage is discharged, it's doing *NOTHING* at all. And there's no such thing as free energy, or 100% efficient energy conversion either, so after that beat and your system is able to sustain 14 volts, the amp won't see 14 volts until the capacitor is charged again. Now the capacitor charges fast, but it's still wasted energy with the capacitor there.
So what are they good for?
They look cool, they impress high-school kids who don't know any better and they make the manufacturers a LOT of money. That last bit is important; it's the reason that they're in virtually every single car that is sponsored or is trying to get sponsored.
So what are they good for?
They look cool, they impress high-school kids who don't know any better and they make the manufacturers a LOT of money. That last bit is important; it's the reason that they're in virtually every single car that is sponsored or is trying to get sponsored.
#4
11-04-2010, 12:02 PM
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I still haven't seen evidence that cap is useless, and stop talking in volts when talking about a cap, its storing charge which provides current to your amp, sharing load with your alternator/battery.
For an alternator,
Case 1) providing 10 Amps for say 2 second
is 4 times better than
Case 2) providing 20 Amps for 1 second.
Alternator will generate only quarter of heat spread over twice the time. Less chances of burning your alternator.
A capacitor lets you do exactly this, spread current needed from the battery/alternator over a longer time frame. Going back to my first post, heat generation in your alternator, current is squared, time is not.
For an alternator,
Case 1) providing 10 Amps for say 2 second
is 4 times better than
Case 2) providing 20 Amps for 1 second.
Alternator will generate only quarter of heat spread over twice the time. Less chances of burning your alternator.
A capacitor lets you do exactly this, spread current needed from the battery/alternator over a longer time frame. Going back to my first post, heat generation in your alternator, current is squared, time is not.
#5
11-04-2010, 04:04 PM
I still haven't seen evidence that cap is useless, and stop talking in volts when talking about a cap, its storing charge which provides current to your amp, sharing load with your alternator/battery.
For an alternator,
Case 1) providing 10 Amps for say 2 second
is 4 times better than
Case 2) providing 20 Amps for 1 second.
Alternator will generate only quarter of heat spread over twice the time. Less chances of burning your alternator.
A capacitor lets you do exactly this, spread current needed from the battery/alternator over a longer time frame. Going back to my first post, heat generation in your alternator, current is squared, time is not.
For an alternator,
Case 1) providing 10 Amps for say 2 second
is 4 times better than
Case 2) providing 20 Amps for 1 second.
Alternator will generate only quarter of heat spread over twice the time. Less chances of burning your alternator.
A capacitor lets you do exactly this, spread current needed from the battery/alternator over a longer time frame. Going back to my first post, heat generation in your alternator, current is squared, time is not.
No sense in re-typing up something well said already:
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 (usable 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 - all 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.
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 (usable 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 - all 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.
And for more in-depth reading: http://www.welcometotheden.8k.com/caraudio/Captest.pdf (you must copy and paste this link, clicking it doesn't work)
The TL;DR of that? Your charging system maintains a slightly lower overall voltage with the cap installed, meaning, your alternator is working harder.
Last edited by Wrathernaut; 11-04-2010 at 04:12 PM.
#6
11-07-2010, 07:01 AM
I know im not a expert in this field and being that i have 5 min left at work until i go home i would add a little input.
Of course I have some experience or else I would not have the ***** to add my 2 cents to this conversation with the experts.
i thought a capacitor was only there to protect against a sudden surge are spark above 12 volts to protect the alternator and other devices
Of course I have some experience or else I would not have the ***** to add my 2 cents to this conversation with the experts.
i thought a capacitor was only there to protect against a sudden surge are spark above 12 volts to protect the alternator and other devices
#7
11-07-2010, 07:11 AM
I know im not a expert in this field and being that i have 5 min left at work until i go home i would add a little input.
Of course I have some experience or else I would not have the ***** to add my 2 cents to this conversation with the experts.
i thought a capacitor was only there to protect against a sudden surge are spark above 12 volts to protect the alternator and other devices
Of course I have some experience or else I would not have the ***** to add my 2 cents to this conversation with the experts.
i thought a capacitor was only there to protect against a sudden surge are spark above 12 volts to protect the alternator and other devices
The marketing behind capacitors claims they're there to provide energy in case there's a need for more than the alternator can give. As pointed out in the above, the usable energy in them after the alternator is overtaxed, and before the capacitor drops below the battery's voltage is so small that it's worthless. Similarly, the energy conversion being less than 100% means that it takes more work for your alternator to fill that capacitor between its discharges than if the capacitor wasn't there at all, so any claims that it reduces strain on the alternator are similarly discountable.
That said, if anybody has any non-subjective evidence showing that a capacitor helps sound, feel free to post it up.
Such evidence would be a graph showing the output voltage at the speaker terminals with a test audio pattern comparing with and without the capacitor installed and without.
Claims of better sound by ears or other anecdotal evidence is not.
If you believe anecdotal evidence of sound quality, I've got some volume ***** to sell you.
Last edited by Wrathernaut; 11-07-2010 at 07:19 AM.
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#8
11-07-2010, 07:38 AM
So from what your saying a cap does more harm than good
I always thought a cap was a added security protecting the car from the high output of a upgraded system.
Also wrathernaut if one wanted the best system setup what would you recommend?
I know your like a fan of jl audio
I was thinking maybe a 4080 enclosure with a jl 10W6 with jl1000/1 with stock Bose head unit or 4080 enclosure with a jl 10W6 with jl1000/1 with jvc kw nx7000 HU I would love to hear you shed some light on this lol
Also explain the pros and cons of the sizes like the difference between 10" and 12" and is it better to get single or double subs
Sorry if it sounds confusing
I always thought a cap was a added security protecting the car from the high output of a upgraded system.
Also wrathernaut if one wanted the best system setup what would you recommend?
I know your like a fan of jl audio
I was thinking maybe a 4080 enclosure with a jl 10W6 with jl1000/1 with stock Bose head unit or 4080 enclosure with a jl 10W6 with jl1000/1 with jvc kw nx7000 HU I would love to hear you shed some light on this lol
Also explain the pros and cons of the sizes like the difference between 10" and 12" and is it better to get single or double subs
Sorry if it sounds confusing
#9
11-07-2010, 08:08 AM
All I know is I had two 1-farad caps installed on my previous car and they definitely helped in a way. Before installation, the headlights would noticeably flicker every time the subs hit. After installation the lights were normal. But, I did replace alternators about every 1.5 - 2 years.
#10
11-07-2010, 02:36 PM
All I know is I had two 1-farad caps installed on my previous car and they definitely helped in a way. Before installation, the headlights would noticeably flicker every time the subs hit. After installation the lights were normal. But, I did replace alternators about every 1.5 - 2 years.
Using a multimeter that attaches to a data logger of some sort can easily sort out whether there is a difference.
I wouldn't say that capacitors do any harm, but they add unnecessary complexity to a system where simple is better, and a charged capacitor is dangerous if you don't know how to handle them.
I like JL Audio, and they're good, but they're more expensive than they are good. Their amps are some of the few that are designed to take differential-balanced signals, so I highly recommend them when somebody's keeping the Bose headunit.
Subs though? I have one, but if I had to buy again, I wouldn't get another 10w6 when there's ones with equal or better sound quality for less. I'd go with a sundown SA-10 or a Image Dynamics IDQ10v3.
For our car, a well-powered 10" is just fine. Some always want more though, but for me, having nearly all my trunk available is always nice.
#11
11-07-2010, 03:19 PM
Ok because I trust your word next system I do I will check the voltage of the car with stock system at high with the engine running and without the engine running
Then I will install the system and check the voltages again
Then check it without the capacitor
I always wondered why the stock system in a BMW hits so hard with superb clarity at all volumes is it because of the fiber optic cabling used I know the cabling is super expensive can it be used or installed in a g35
I have a 2005 BMW 530i and I wanted to install a system but I was doing some reading first
Then I will install the system and check the voltages again
Then check it without the capacitor
I always wondered why the stock system in a BMW hits so hard with superb clarity at all volumes is it because of the fiber optic cabling used I know the cabling is super expensive can it be used or installed in a g35
I have a 2005 BMW 530i and I wanted to install a system but I was doing some reading first
#12
11-07-2010, 06:25 PM
You'll need a very high sampling rate on your datalogger, just throwing a multimeter won't be able to show a whole lot.
BMW has some good premium systems available, but I wouldn't say the base audio system in the 2009 M3 coupe I drove for a couple weeks was anywhere near as good as the system I've installed in my G35.
BMW likely is using the fiber for other reasons, not noise reduction. Fiber's used for transferring digital audio when you're sending a digital signal like Dolby, Surround, stuff like that. My guess would be to send 11 or 12 channels, or however many the premium systems in BMWs use these days, without needing to send 20+ wires just for audio signals to the amp.
As for fiber optic for audio in you car, whatever you'd have to do to use it, ain't worth it. Any minor noise reduction would be completely trumped by the sound of your own breathing. Shielded RCAs in a car that acts as a decent Faraday cage to begin with is plenty.
BMW has some good premium systems available, but I wouldn't say the base audio system in the 2009 M3 coupe I drove for a couple weeks was anywhere near as good as the system I've installed in my G35.
BMW likely is using the fiber for other reasons, not noise reduction. Fiber's used for transferring digital audio when you're sending a digital signal like Dolby, Surround, stuff like that. My guess would be to send 11 or 12 channels, or however many the premium systems in BMWs use these days, without needing to send 20+ wires just for audio signals to the amp.
As for fiber optic for audio in you car, whatever you'd have to do to use it, ain't worth it. Any minor noise reduction would be completely trumped by the sound of your own breathing. Shielded RCAs in a car that acts as a decent Faraday cage to begin with is plenty.
#14
11-09-2010, 02:50 AM
I have:
JL 300/1v2 (Speakers)
JL 500/1v2 (Sub)
4080 Enclosure
JL 10w6v2
BA Pro60se's up front
BA SC65's in the rear
Pioneer Z110BT
sounddeadenershowdown.com CLD tiles in the trunk and on one door (didn't finish before deploying)
dynamat is crap, but it's easy to buy locally, but the SDS CLD tiles are much better in terms of price, adhesion and vibration dampening.
JL 300/1v2 (Speakers)
JL 500/1v2 (Sub)
4080 Enclosure
JL 10w6v2
BA Pro60se's up front
BA SC65's in the rear
Pioneer Z110BT
sounddeadenershowdown.com CLD tiles in the trunk and on one door (didn't finish before deploying)
dynamat is crap, but it's easy to buy locally, but the SDS CLD tiles are much better in terms of price, adhesion and vibration dampening.
#15
11-09-2010, 11:04 AM
Dynamat is easy to buy locally but if I can buy something better I would wait for it so I can just do the job once and get it over with and have immediate Gratification.
Isopod try the cld tiles next time
I don't think pioneer HU have detachable face so that something I would never do again
I take it you like the 4080 better than the zenclosure I'm hearing the zen sucks
Did you not like the stock speakers and amp
Isopod try the cld tiles next time
I don't think pioneer HU have detachable face so that something I would never do again
I take it you like the 4080 better than the zenclosure I'm hearing the zen sucks
Did you not like the stock speakers and amp