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Old 6th July 2011, 07:00 PM   #1
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Default Real Capacitors

I'm not sure why people buy those "car audio" capacitors when computer-grade capacitors have a lower ESR, higher current rating and can dump all of their energy near-instantly without damage.

Here is a picture of my capacitor bank. Since my hobby is a bit different from yours it's a 700V 24800uF bank, but the same construction would apply to low voltage capacitors. Although if you get a big enough capacitor you wouldn't even need busbars. Large real caps do exist, such as the 1F 25V cap on this vishay datasheet.
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Old 6th July 2011, 10:35 PM   #2
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Computer grade caps are OK. Well designed and what not for their intended purpose, but they usually cost significantly more then the typical grade devices used by most audio manufacturers. And they are usually huge size wise in a use where small size is very important. It's all a matter of build costs and physical size limitations IMHO. Also most likely due to limited discharge rates required for audio, and the huge discharge rates and internal heat build up for industrial usages like lasers, flash tubes, and rail gun technology's.

Plus in large banks like yours, variances in ESR and voltage drop across each individual capacitor comes into play and usually requires some form of active or passive control method such as resistors < passive> or diodes < active> to equalize drops and current sharing issues associated with very large capacitor arrays.

I don't claim to be anywhere near expert in the area but, in most cases where large arrays of any device are used, high precision tolerance matching usually comes into play so each individual device performs equally, and or some active or passive matching networking is designed into the scheme just to maintain electrical uniformity of operation. This includes those large SUPER caps used in electric cars also. They even advertize either active or passive methods in their option spec's. Presumably due to their extensive use of very large cap arrays such as yours. Since they manufacture cap banks I am guessing they have a firmer grip on the technology then me.

PS the largest cap bank I ever saw was at the Lawrence Livermore Labs used on the Fusion project they have going on their. < it's online if you care to take a look, just Google Fusion LLL > The cap bank was the size of a high school gym as I recall. The steel beams were coated with fire retardant just in case the room was to go up in flames so the steel would have some fire/heat protection for a while.
I am guessing by your 700 volt rating your either into high power discharge devices such as laser's and flash tubes or perhaps small rail gun technology. All very neat stuff...Most car and home audio is designed and built on a much lower level of technology, with a very high safety factor involved.

Large cap array's can be very volatile upon failure, Fire, explosions and so on. This is also probably another reason why you don't see such huge efforts at energy storage in audio. it can be very dangerous to the inexperienced and unqualified..

Last edited by 1moreamp; 6th July 2011 at 10:46 PM.
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Old 8th July 2011, 03:31 AM   #3
jol50 is offline jol50  United States
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Audio only needs so much storage anyway, people can buy huge caps they just don't they buy a larger alternator.
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Old 8th July 2011, 03:58 AM   #4
ppia600 is offline ppia600  United States
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Lower voltage high capacitance caps were more difficult to manufacture but are getting more inexpensive. The higher voltage lower capacitance ones have been easier to make for ages and of course you can get them for less. You can build a large bank with electrolytics or carbon foil types but by the time you add in material cost, size, and performance for the same single aftermarket version you end up spending more. Why would you buy sixty kazillion electrolytic (or carbon) smaller capacitors and spend all of the time fitting and building the rail system and even having to design the resistor equalizing circuits mentioned above when you could just buy one 20-25farad low voltage cap for $100? I'm not saying I like sending $100 to some random asian factory but I also don't want $15-20lbs of stuff taking up space in my vehicle that I could be using for other things. Yeah, individual "super" or "ultra" caps seem cheap but multiply how many you will need to achieve the same capacitance times the other materials and time you spend building it. Yeah, its nice that we can build them but why?
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Old 8th July 2011, 04:30 AM   #5
JZatopa is offline JZatopa  United States
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second battery > cap.
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Old 8th July 2011, 05:09 AM   #6
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All good points.

Quote:
Originally Posted by DJNUBZ View Post
second battery > cap.
This is a good point too. I have an AGM battery that can well... do this.
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Old 8th July 2011, 01:11 PM   #7
Cr@sh is offline Cr@sh  United States
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They make 50 farad caps but like others have stated there useless in car audio applications at least for high output spl.
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Old 9th July 2011, 06:19 AM   #8
ppia600 is offline ppia600  United States
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Quote:
Originally Posted by DJNUBZ View Post
second battery > cap.
as long as its not a tiny flooded plate lead acid battery, agm's are best imo

Quote:
Originally Posted by grenadier View Post
All good points.



This is a good point too. I have an AGM battery that can well... do this.
I do as well but high farad caps are great at filtering ripple from the alternator, and are getting smaller.

Quote:
Originally Posted by Cr@sh View Post
They make 50 farad caps but like others have stated there useless in car audio applications at least for high output spl.
Caps are not useless, so much heresay in this thread. Have you ever tried batcaps? "If its on teh intarwebz it must be true"
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Old 9th July 2011, 08:25 AM   #9
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Here you go guys. Some ULTRA CAPS

Electric double-layer capacitor - Wikipedia, the free encyclopedia


I like bat caps and have recommended them a many a time in the past, but not since these puppies became available. Their is a guy selling a 7 cap stack and he starts a diesel engine with them. And another fella on tube runs a color 32 inch tube tv for 10 minutes with a 5 stack of the 2600 farad units, its only about 500 farad real world at 12 volts to a inverter.
Be fore warned though, don't allow any one of these individual caps see over 2.5 volts Dc to them. You have to stack them for higher voltage use. I even saw a 125 volt and a 48 volt one on that auction site. Pre-built ready to run, and about 180 pounds to lift and carry...Yes Sir ULTRA CAPS

Oh and don't forget the voltage balancing circuitry across the cap stacks to keep the voltage to each cap at or below 2.5 volts max. This is that balancing circuitry I mentioned in my earlier post. It is very important for safety and life expectancies reasons if you build a stack of these puppies...and please be very careful when working with large capacity systems...

Last edited by 1moreamp; 9th July 2011 at 08:29 AM.
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Old 9th July 2011, 12:48 PM   #10
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Those supercaps suffer from high esr, so I'm not so sure about their filtering capabilities. They are usually used for storing energy during regenerative braking on e-cars.
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