Vote and reason why, can a Cap improve, be a band aid or a waste of Farad? - diyAudio
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Old 31st December 2008, 02:00 PM   #1
mikee55 is offline mikee55  United Kingdom
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Default Vote and reason why, can a Cap improve, be a band aid or a waste of Farad?

Just a thread for fun or usefullness Whats the word on Capacitors?

Mikee55
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Old 31st December 2008, 10:38 PM   #2
mikee55 is offline mikee55  United Kingdom
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Default Shall I start then?

I vote it as a band aid. Your go then
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Old 1st January 2009, 12:18 AM   #3
MadMutt is offline MadMutt  Australia
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Waste of money.
You already have one of the biggest caps possible in the car.
The battery.

If your getting voltage sag, you need to go back to basics.
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Old 1st January 2009, 01:40 AM   #4
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I think they can be useful,but they're often way too over-hyped. They aren't going to 'fix' anything.

Useful,but often (mis)used as a 'band aid'
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Old 1st January 2009, 09:44 AM   #5
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Here are some things I have read that sound good:

"a power capacitor is placed much closer to the amplifiers than the battery is so that voltage drop is going to be much less all other things being equal. But second, your charging system probably isn't designed to provide current draws that large at any time. So your amplifiers are going to have to get the power from the vehicle's battery as well as the alternator. And the battery has its own internal resistance which, as stated before, is much higher than that of a car audio power capacitor. Because of this extra internal resistance it is not an effective means of delivering large amounts of instantaneous current. The capacitor acts like a small tank with a large hose while a battery acts like a large tank with a small hose. So with a capacitor installed you can deliver a large current burst during a music transient and then the capacitor can recharge during the non-peak portions of the music."

"The ESR of a battery is much higher when it's being charged. A battery's natural voltage is about 12 volts. It is at this voltage that it can deliver real current. When it's being charged, its voltage is raised above 12, but it will quickly drop to 12 volts under a load. This is what we refer to as "surface charge."

When the amplifier draws a lot of power the battery can't deliver much current until it drops to 12 volts. That's why the lights flicker much more when the engine is running. The alternator is normally charging at 14.4 volts but when the amp draws a lot of current, the voltage briefly drops to 12. This is because the alternator's regulator is very slow to respond. I guess you could say that the battery isn't in the circuit until the voltage drops to its natural cell voltage."

"The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge. That's why the electronic flash on a camera uses a capacitor "
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Old 1st January 2009, 11:36 AM   #6
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You can not even buy a stiffening capacitor from the retailer at which I work. It did not take us long to figure out that it was not doing anything to help the dimming headlight problems that people were purchasing them for. In order to remain a reputable shop, we refuse to sell them. So now if a customer comes in and requests a capacitor for their system we are installing, we try the best we can to convince them that the cap is going to do nothing to rectify the dimming headlights they are concerned with. Their answer is always the same, they must work, my boy has one and his lights do not dim at all. Then they ask, if I go get one will you install it. Of course we say yes. They leave and come back an hour later, proudly toting the cap in one hand and the lighter wallet in their pants pocket. We install it and then they get mad at us because their lights are dimming. Come to find out, their boy has 2 10s on a 400 watt amp and we just put 2 3000 watt amps on his 6 13.5s.

I have told the boss we should get some for the ones that insist we sell them one, she refuses to knowingly help them throw their money away.
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Old 2nd January 2009, 08:20 PM   #7
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I had one successful implementation of a capacitor in my 1996 Thunderbird, and it was for an issue that was NOT advertised. I installed it to get rid of a noise problem that had several other installers as well as myself baffled. After I put the capacitor in my system, the noise went away.

A friend of mine from here, who moved out to California when he joined the service actually recommended the cap to solve the problem! IIRC a huge capacitor can filter out high frequency noise, but I never understood why the filtering caps in the amp couldn't handle that duty
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Old 3rd January 2009, 06:06 PM   #8
jol50 is offline jol50  United States
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Seems obvious to me a typical cap holds a tiny amount of power. If you need that tiny amount of power for an instant to fill in a lag, then sure it will work for that purpose. So if you are right on the edge of capacity it may help, just seems most are way over what the car can produce so it is not going to help that. It will filter too, and I've been told it can help lifespan of other electronics in the car as well as alternators. I agree its not going to do that much. Seems proper use for power issues is to get a huge alternator and huge bank of caps, then you can run 14.4v solid long as the caps cover the regulator lag and you don't overdraw what that alternator puts out. Aside from that you just need more battery to keep from dropping under 12v, if you don't go the big alternator route or play it with car off.

Would be great if someone could give more detail how a cap might affect other electronics in the car or the voltage regulator. I was told on an amp hit it would drain the input caps of anything in the car and a large cap on the amp might help it not do that so much. I got a 1f for $15 I will try, I figure it can't hurt. But also I am not running that much power likely will stay under 600-800rms total and I think I have a 125A alternator. I get a slight pulse in lights without one, but not bad. I fail to see how a cap could hurt, though it may not be worth the money you could use for other improvements.
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Old 3rd January 2009, 06:28 PM   #9
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Quote:
Seems proper use for power issues is to get a huge alternator and huge bank of caps, then you can run 14.4v solid long as the caps cover the regulator lag and you don't overdraw what that alternator puts out. Aside from that you just need more battery to keep from dropping under 12v, if you don't go the big alternator route or play it with car off.

I think this is a key problem. People don't seem to understand that *ALL* of that power,has to come from the alternator.Once the car is started,it's not running on the battery anymore,the alternator is supplying all the power for the car. The battery will come into play if you draw a large load,and the voltage dips..the battery will 'buffer' it. A cap does something similar,but on a smaller,faster scale.

A cap does *NOTHING* if your alternator cannot support the load.

The bottom line is: Your alternator must be able to supply the current needed by everything. *THAT* should be your first upgrade.
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Old 3rd January 2009, 07:03 PM   #10
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Quote:
A cap does *NOTHING* if your alternator cannot support the load. The bottom line is: Your alternator must be able to supply the current needed by everything. *THAT* should be your first upgrade.

Well said and SO true. I have seen car battery's dip to 8 volts on heavy load as they are SLOW to meet the demand also, and cold they are even slower. Or they are just being loaded beyond there rating so badly that they drop output trying to supply current.

Some alternators are also slow, and all have High Temp current limiting inside then as built in protection for the diodes and such. And there output is Shaft Speed dependent. If its not turning enough RPM then its just not capable of handling the load also. Hence the use of smaller over-drive pulleys to rev up the shaft speed at idle. But this adds limitation on high RPM speed also.

Adding a properly spec'ed cap can improve noise issue somewhat, and can buffer the slow responding charging system and battery, and help out a little bit on many of these things. But its not a properly engineered solution unless all of these facts and data are put together to get a clear overall picture of where the problem is. Some things need to be directly addressed before anyone should even think about adding a cap system.

BUT most people just have no idea how all this stuff works and what the variables are and how they effect the overall performance of the charging system, and eventually the car audio system. Hence the "Bad Bandaid Rap" Caps have.

Dealers spend X time building up a system in a car and never even look at weather the car can actually handle the load that is getting installed. It reminds me of a picture I had sent to me of a donkey cart tipped backwards lifting the Donkey into the air. Funny how stuff like that happens. Sell 10 Grand of car gear and install it on a car that can barely keep its head lights on when running...lol lol lol Seen it a million time it seems like over the years ..lol lol lol and everytime I see that poor Donkey in mid-air in my mind ...Lol lol lol
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