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Unread 03-24-2004, 05:31 PM   #1
phokur
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Choosing a Capacitor

I am searching on ebay, and I know I need a capacitor to help out my alternater. I have a 1200watt amp, and 3 10" MTX subs. I am browsing ebay, adn they all seem pretty expensive. I think I only need one farad, and I have heard good things about Stinger and RF, but which are worthe the money? I see some cheapo ones, would they need to be name brand to work well? I wouldn't mind spending money for a good one, but I rather not if I could just buy one of the cheaper ones.

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Unread 03-25-2004, 08:57 AM   #2
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Quote:
Originally Posted by phokur
I am searching on ebay, and I know I need a capacitor to help out my alternater. I have a 1200watt amp, and 3 10" MTX subs. I am browsing ebay, adn they all seem pretty expensive. I think I only need one farad, and I have heard good things about Stinger and RF, but which are worthe the money? I see some cheapo ones, would they need to be name brand to work well? I wouldn't mind spending money for a good one, but I rather not if I could just buy one of the cheaper ones.
1200W RMS? You need 2.5 farad for best performance. If your reading the scribble on the amp saying 1200W of power it's probably 300-600W of actual RMS output total so 1-1.5 farad would do you. The rule to follow is 1 farad per 500W of power or 1/2 farad for 250W. All power should be measured in RMS always as MAX potential doesn't mean anything usable 99.9% of the time.

Mostly, all caps are the same. There are some other options though like The C.A.P. which is basically 5 (versions of 15 and 50 available too) farads of capacitance in a very small package that cost about as much as 3 full-sized 1 farad caps. (kinda like buy 3, get 2 free and all in a small package)

But as for the cans style caps (standard round) they are almost identical. Very simple to build and not much stuff they can do custom to them accept add digital tops or distribution blocks or something of that nature. RF caps, lightning caps, scosche, streetwires, anyof them should be fine. (though I would get the audio specific models made by ONE of the audio companies as some bulk caps for engineering don't have the safety fluid break in them to prevent meltdown should a problem occur. All of the audio one's do...)
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Unread 03-25-2004, 04:12 PM   #3
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What's the problem? Caps provide so little for what they cost that I wouldn't bother. Are you dropping voltage? Cap won't fix that. Do the lights flicker to the beat of the music? A cap can help a little in that regard. Upgrading the grounds and alternator charging wire (aka the big 3 or the magic 3) will usually help quiet a bit.
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Unread 03-25-2004, 09:22 PM   #4
phokur
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Well last Jeep I had this system in, my alternator blew up. My lights would flicker really badly when I cranked the music up. I was only running half of my amp and it just died. I heard if I had a 1farad it would of helped me. I wouldn't need any more. I am not trying to have a perfect system, I just want to avoid replacing my alternators every week.
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Unread 03-26-2004, 09:12 AM   #5
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Quote:
Originally Posted by Jimi7
What's the problem? Caps provide so little for what they cost that I wouldn't bother. Are you dropping voltage? Cap won't fix that. Do the lights flicker to the beat of the music? A cap can help a little in that regard. Upgrading the grounds and alternator charging wire (aka the big 3 or the magic 3) will usually help quiet a bit.
Caps infact CLEAN the power signal (if in-line) to the equipment and also supply current-on-demand. They are pivital in getting the most out of your system.

They will not make up for a lack of charging system capability but they will maintain current for the split second the amp demands it and it will reduce the stress on the charging system of the punchy demands of high-output amps.

So if you think they are too expensive.. Dump a few batteries and alternators and see how cheap they start to become. Besides saving the charging system and improving the power signal to the audio/video system, it can also, by doing so, reduce the chance for a current spike in another device and causing a problem there too because the alternator charge has a place to store and doesn't cause standing current spikes.

If you don't believe they are worth the money, that's your option. And they aren't required for every install either. They are also NOT a replacement for an incapable charging system. They also do not add more strain to the charging system as some people believe but infact reduce it. And honestly, for a powerful system, I can't think of a better bang for the buck in performance than getting a cap. $50-$100 for a quality 1 farad (per 500W RMS) is nothing compared to replacing an alternator, battery, and what ever else you damage. And there's no cheaper way to get clean power to improve SPL and SQ at the same time. Will the CAP itself magicaly improve SPL/SQ? No... but it will supply the clean, more stable power to the amplifier to help it perform at it's best.

They ARE worth every penny when used appropriately.

Quote:
Originally Posted by phokur
Well last Jeep I had this system in, my alternator blew up. My lights would flicker really badly when I cranked the music up. I was only running half of my amp and it just died. I heard if I had a 1farad it would of helped me. I wouldn't need any more. I am not trying to have a perfect system, I just want to avoid replacing my alternators every week.
The cap will help with light flicker because it stores power needed for the amps and more slowly and fluidly recharges from the alternator keeping the current flow of the electrical system more even and smooth. However, if you had such a large system in your old vehicle that it was REALLY pulling in the juice, more so than your alternator could ever fathom of keeping up with, then it's not going to help you too much. It will still perform it's duties but without a sustainable source, it can't smoothen out and maintain the needed power level.

If that is the case, add caps and a more capable charging system. most factory alternators have on average 30-50A of extra capacity. Once you run beyond that, you need to upgrade. This is just a base-line area and every vehicle is different. The more electronics you have on it (the more loaded it is) the less extra charging room you have left!
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Quote:
Originally Posted by SirGCal
If you can't take a nano-second to press shift/period/etc. and make proper sentences and paragraphs, I don't know if I can take a few minutes to respond to your topics... It doesn't have to be perfect by any means, but a little effort goes a long way.
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Unread 03-26-2004, 11:42 AM   #6
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1 Farad per 500rms is the general rule of thumb and any of the name brands should work fine. Just make sure you're looking at the amps RMS output not it's peak or max output.

IMHO caps do very little. Richard Clark has a nice article showing how a cap actually reduces average system voltage during high demand passages, which makes sense since caps aren't 100% efficent. Isn't that exact opposite of what we're trying to accomplish? Sure your lights will flicker less, that's because you're voltage is fluctuating between 12.4v & 13.4v vs 12.4v & 13.8v. Will those fluctuations be smoother - yeah but so what?

http://www.welcometotheden.8k.com/caraudio/Captest.pdf

When the heavy bass hits the cap will fill the current/voltage void before the battery kicks in with it's current or the current demands drop. I certainly wouldn't pay $50-$100-$150+ for a cap for the .05 seconds of benefit it provides before becoming a drag on the system (as it recharges). OTOH you can upgrade the big 3 for ~$20 or get a high output alternator (additional drag on the engine though) for ~$175-250. Those things will actually increase the system's ability to deliever the current high power systems demand.

IMHO people just recommend caps everytime they hear about flickering lights, voltage drops, etc, without understanding how they operate and what they accomplish.

Last edited by Jimi7; 03-26-2004 at 12:57 PM..
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Unread 03-26-2004, 12:59 PM   #7
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The problem is 'dirty in' = 'dirty out'. You can't make clean SQ with dirty power. Even more power (over-powered alternator) is still a dirty signal. The cap cleans the signal and improves SQ capability.

The cap recharges off of access current on the line so there is not additional draw that directly effects the audio system. The sistained draw on the alternator is higher in that sence yes, however it is smoother and less impulsive resulting in less stress on the components.

It's probably from my competition experience but I have seen the benefits of caps. We had a few cars that were SQ class back in the day when the caps were less common. We were trying to get more SQ from these vehicles and the problem continued to be dirty power. Without going over our power limit for the class, we were running out of options to clean up the system.

Installing the caps in that system allowed us to get two points higher (2 dB) on the clean SQ chart. We were able to get a measured clean increase in amp output by an average of 6% per amp because the signal was clean (didn't drop quickly and maintained a good 14.2V average (tweaked regulator) which resulted in a higher clipping range than the average of 13.8 we were getting before due to the high drop-out rates.

Looking over the charts you linked to... This is what I see. (First responce) It looks like he did not have enough capacitance for the amplifier he was using... So the effect he saw was that the cap couldn't handle the load, resulting in a lower performance than otherwise expected. And/Or that the charging system is insufficient.

After reading:

He states at the bottom that it was a 2KW system (I have to assume RMS due to his apparent knowledge level) that was driven right to the point of clipping (distortion).

The first problem is the stock 80 amp alternator (as stated in the same paragraph)... This is NOT going to be enough even if the amp is the only thing running... As I said before, the cap is NOT a replacement for lack of charging system.

He states that he is using a "15 farad type" cap. I must assume that this is not a true cap but something like the alumapro-type caps which are diecent, but not TRUE caps. They are about 95% I'd guestimate in performance. But even so, the alternator can't keep up.

He admits to over-driving the alternator in some tests which we already established is incapable of dealing with a 2kW amp. He seemingly loaded this test from the start.

His wire might also be a factor. Current travels on the surface of the wire which is why large audio systems use extremely high strand-count wire. If he skimmped on the wire, that can be a HUGE factor, espically with a system as powerful as he's running. Infact, with that load I would run a 2 AWG or 0/1 AWG just to be sure the 'pipe' is large enough...

None of the charts I've made in the past have ever been as dirty as he is showing here. Every system will have fluctuations but I don't know if he's got a bad cap, didn't pre-charge, really really bad alternator or what but even for overloaded alternator, that signal is pretty dirty with 15 farads...

I want to see his results of a similar test with a true cap (or pair), 500W RMS amp (more realistic) and ample alternator... It won't show the same results if he gives it an honest try. At least none of mine have ever looked that bad...

You are right in the sence that a cap is NOT the savior of the audio world; it should be though of as more of a power-line conditioner and noise filter than anything else. Is it worth it? That's up to the owner/designer. But at $50 a farad and cheaper (my cost), I put them in every system I do. You can't put a price on clean power when your competing for clean sound... (like drag racers going for another .01 of a second...) Does the back-yard guy need it? If the $ is there, sure.. No one can have enough clean power... But is it required? Or will it give you 3dB simply by sticking it on? No... It might help you gain a few dB after adjusting your system to the new power level average, but it won't directly give you plug-in power... I don't know anyone who ever said it would. It's an incorrect assumption by many people...

If you don't wana use em, that's entirely up to you... I will.
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Quote:
Originally Posted by SirGCal
If you can't take a nano-second to press shift/period/etc. and make proper sentences and paragraphs, I don't know if I can take a few minutes to respond to your topics... It doesn't have to be perfect by any means, but a little effort goes a long way.
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Unread 03-26-2004, 01:40 PM   #8
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All good points SirG. RC kinda uses the extreme to illustrate what's happening. I do assume he's using proper wiring, etc, given his history in car audio.

I guess my original point to the OP is that cap money would be better spent elsewhere, ie upgrading the magic three, which is cheap and works 80-90% of the time. A HO alternator doesn't cost much more than a cap and provides more current where as a cap just stores current.

Also I have to point out that Caps don't charge off excess current. They charge to whatever the line voltage is. So if high power system hits a bass heavy passage and the voltage drops to ~12v the cap will be charging the whole time as the system recovers and returns to ~13.8v. There is no excess current as the cap is charging from 12v to 13.8v, as a matter of fact there is a lack of current.

Now if we're talking competition systems where people are doing everything possible to get a point, I see some benefit to smoother voltage fluctuations. IMHO for high power systems, big 3, HO altenator or extra battery or batcaps, and a cap would be the last on my list.
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Unread 03-26-2004, 02:06 PM   #9
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I think you mis-understood my intention when I stated access current.

The cap, when correctly installed in these systems, usually never has to charge when under max current request from the amp. The amp current request is in a much lower state on that portion of the curve however the alternator is already pumping out alot of current. The alternator maintains the higher level of current, thus charging the cap again. It's not that it charges off some left-over current that just hangs in the system... Most of the time it can charge during amp-draw low-time.

Remember too that the peak currents are only for hundredths of a second and a good 1farad cap can sustain the charge that an amp would call for for a good second or two. Even though they also have the ability to dump it all in a split second, they only dump what is needed. So they very rarely, if ever, dump completely. They dump current on the rise of the wave and recharge on the drop of the wave while the alternator maintains a constant current output demand all the time (or tries too). (this is, of corse, assuming a sign-wave input requirement of the amp. Perfect world scenerio.)

But that's what I ment about recharging off of excess current... I hope it makes more sence this time...

As for the big three, as you put it... Yes.. I would also always put them first. Alternator, regulator, battery AND also all at the same time (due to electrical memory which is just more extremist overkill). But I would also stick some caps in there. The way I see it: If you spent $3000 on hardware, and another $500-$1000 on charging system and quality wire, what's another $50-$300 to be SURE it's clean and protected... BUT, do I use them all the time? No... Some systems just don't need them and would recieve no practical benefit from them...

I think we are on the same page.. We just lean twards the opposite extreme of the theory and practice.. Which is good! If we all agreed 100% on everything, the world would be pretty friggin boring...


NOTICE to onlookers:

I hope other people reading this thread realise that Jimi7 and I are neither one wrong from an opinion's point of view. And not arguing against each other directly, but on the theory of the capacitor. Both of our reasoning is dead on and both arguments are valid. They are simply different points and areas of the same opinion which lead to slightly different output results.

It is up to you, the owner/builder to decide if the cap is right for you. Jimi7 and I are just putting out our precieved views of the situation. Will they help you? That's really, as you can probably now tell, up to your specific situation and current installation situation. Are they the 'magic solution' to all your charging problems? Hell no... THAT... is the misconception about them...

And for that part of the argument, I have to concede to Jimi7.. For the back-yard, home install to benefit noticably from a cap, it would have to be riding on the edge of the alternator balance... Your alternator would have to be running at peak output most of the time but still holding on... Otherwise, the benefit is mostly only going to be noticed with expert tweaking and monitoring equipment. ALTHOUGH... Your car may thank you if you do install one cause it does help clean up some of the steep current/voltage alterations. It might save some of your vehicles electronics down the road too... Power issues of one form or another account for 98% (if I remember correctly...) of all in-field electronic failures in the world today.

Good Discussion Jimi7.
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Quote:
Originally Posted by SirGCal
If you can't take a nano-second to press shift/period/etc. and make proper sentences and paragraphs, I don't know if I can take a few minutes to respond to your topics... It doesn't have to be perfect by any means, but a little effort goes a long way.
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Unread 03-26-2004, 02:22 PM   #10
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Agreed, SirG - and ultimately it is about having the knowledge and then deciding if a cap is right for you - just like one would research any performance upgrade.

One warning to anybody considering a cap - walk into any car audio place and tell them your lights flicker, etc, and the standard answer is spend $100 on a cap. Rarely do they take the time to find out what equipment you're running, alternator output, wiring, battery, etc. So how do they know the cap is the solution? For all they know it's corrision on the battery terminals, a dying alternator, etc. That is part of my problem with caps.

OTOH I've seen upgrading the magic 3 and voltage problems go away. BTW magic 3 = the alternator charging post to battery 12v+, the ground from the block to the battery and from the chassis to the battery. Just add 8-0awg wiring to the existing wiring (depending on current draw). Cheap and easy and works.
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Unread 03-26-2004, 02:33 PM   #11
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Agreed Jimi7, On all points in your last post.

I so often forget that I know what I'm doing that I also forget the results people will recieve when they go into an average store asking for advice.

Jimi is right. They often don't check your setup...
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Quote:
Originally Posted by SirGCal
If you can't take a nano-second to press shift/period/etc. and make proper sentences and paragraphs, I don't know if I can take a few minutes to respond to your topics... It doesn't have to be perfect by any means, but a little effort goes a long way.
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Unread 03-26-2004, 03:10 PM   #12
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WoW, sorry it took me so long to respond... I didn't expect this many posts...but thanks! Ok, I am pretty sure the peak on my amp is 1400. I can't tell the rms, I don't have the book. Here are the specs from the site: http://www.pyramidcaraudio.com/itemp...p?model=PB1080

I am geussing/hoping for 750rms, because that is my sub's max rms. Also, my headunit had mosofet power, would it pass that to the subs to? I put the system in my last with pretty thick wire. And I ground it in two areas just to make sure.

I am looking around on ebay and I see alot of capacitors going for all different amounts. I will gladly pay $30-$60 if it would help me out that much. I will certainly upgrade to the "big three" down the road, but after spending $1500 on a lift and wheels I don't have much money right now. But it's something to save up for.
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Unread 03-26-2004, 04:35 PM   #13
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That's a 4 channel amp... Not usually used for subs... I would put my money on the fact that it is really:

175W x 4 @ 4 ohms.
350W x 2 bridged channels @ 4 ohms.

NOT 2 ohm stable bridged.

That's not a sub amp from the looks of it but the stat page sucks and the site isn't very helpful...

Which MTX subs you you have exactly?
Single or dual voice coil and how many ohms per coil. (they should say somewhere and it's extremely important to setup and amp selection...) I might be able to tell from the model numbers.
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Quote:
Originally Posted by SirGCal
If you can't take a nano-second to press shift/period/etc. and make proper sentences and paragraphs, I don't know if I can take a few minutes to respond to your topics... It doesn't have to be perfect by any means, but a little effort goes a long way.
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Unread 03-26-2004, 05:16 PM   #14
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My subs: http://www.crutchfield.com/cgi-bin/S...610X3D&o=m&a=0
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Unread 03-26-2004, 07:38 PM   #15
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I tend to agree with SirG on this issue. My colleagues and I have argued this one endlessly before. I believe the technical merits have been presented quite well, but here is my .02.
1) There is nothing detrimental about a reservoir of power immediately adjacent to the amplifier(s)
2) When the battery recharges the cap, it does so at a fairly steady rate, eliminating sudden spiky drains on the electrical system.
3) Capacitors of the smaller variety are used in many applications(especially CB installs) to decrease dirty power, the larger versions also show this benefit.

I personally use a 1 farad Monster Cable digital capacitor(since every little bit of my system is wired with Monster). The benefits to several sets of professionally trained ears were immediately apparent. I have Alpine 3547 & 3548, an MTX 2150x and an AudioControl 2XS crossover. Since my jeep is always providing sound when tailgating and camping, I can check my power level and restart the engine as necessary. Underpowered amps=speaker damaging distortion.
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