just curious. i have some fun to post on them in a little bit, just want to see who still uses them.

 

i have one in my car. got a 600w amp and a 1 farad cap. when my alternator goes out i am goin to upgrade it and prpbably sell the cap. the cap does work great, no dimming at all and it looks cool. at the time i bought the cap, i got a really good price on it, so i got it

 

one here. 1 farad with a punch 800

 

Only use them when they are needed. Some amps have built in caps, not just ones for filtering but also for quick electron discharge.

I use a basic rule of thumb, for ever 1kw rms = 1f cap

 

i got a 2 farad cap in my setup.

 

i have 2 one farad caps and 2 400wrms amps. seems to work fine. they just recently aided me in some electrical gremlin diagnostics so i guess they are good for something.

 

i assume you also follow the rule that any capacitor with an ESR over 0.002 ohms is relatively useless?

here's my own personal novel on capacitors:
we've all heard of the case where someone just installed a sub/amp combo that does 500 watts and their headlights and interior lights are dimming when the bass hits. supposedly, the miracle fix is a 1 farad capacitor which suddenly stops this from occurring. i'll start off by saying a little background info about capacitors.

capacitors are constructed by separating two or more conductors called plates with an insulator called a dielectric. if an AC signal is applied to a capacitor's plates, the current will flow through the capacitor. what actually happens is that if an AC signal is applied to the plates, the capacitor will charge one way (hence current flows), then when the AC signal reverses direction the capacitor discharges and then charges in that direction. this makes it appear that the AC current is flowing through the capacitor. a DC voltage connected to the same plates will not pass through the dielectric, and no direct current will flow through. therefore, this capacitor will accomplish a few things: it will block most DC current (accessory noise suppresion), and it will store an electrical charge that can be used later.

now in theory, if your alternator is correctly charging the battery, then the battery will do a much better job of blocking DC current from being sent signal-wise and also produce the required amperage to power your vehicle and your vehicle's sound system. so why is a capacitor used? i personally don't use them except in show situations, however i imagine that in many applications, a capacitor is a more affordable solution than getting a new alternator and battery when you are only having a small power problem. also, it is likely unrealistic that a battery will do a perfect job of filtering DC current.

this is not to say that a capacitor is totally useless. it does a quality job of filtering voltage ripples, minimizing both the dips and the peaks in your system voltage. this is why they work in systems where the alternator is just barely short of producing the required amperage and you experience dimming.

but let's consider other situations, shall we? i mentioned ESR earlier. this is the effective series resistance of the capacitor (everything has resistance). a capacitor with an ESR rating higher than 0.002 ohms starts to become useless as it causes a certain level of voltage drop at the amplifier. the issue lies in the fact that a lot of the capacitors widely available have ESR ratings of 0.003 or higher. even worse, the large farad capacitors, which store the most energy, also tend to have the highest ESR ratings. here's some numbers to consider:
ir=v
where i=amperage of system
r=ESR rating of the capacitor
v=voltage drop experienced

100*0.001=.1V :this correlates to 14.3V system
200*0.001=.2V :this correlates to 14.2V system

that's not too bad. let's setp it up a bit to something you're more likely to find.
100*0.003=.3V :this correlates to a 14.1V system
200*0.003=.6V :this correlates to a 13.8V system

now for the drastic example. this is a 40 Farad capacitor with 0.03 ohm ESR rating. this is from a major company that we recently dropped from our sales floor.

100*0.03=3V :this correlates to a 11.4V system
200*0.03=6V :this correlates to a 8.4V system

pretty sickening. of course, 200 amps correlates to roughly 2500 watts, which isn't necessarily something everyone would go with, so i picked an example right out of my girlfriend's grand am.

1 JL Audio 500/1 with a capacitor with an ESR rating of 0.005 ohms (this is straight out of their owner's manual)
p=iv
where p=wattage
i=amperage of system
v=voltage
so,
500=i(12.6)
i=~40 amps

back to the ESR calculations:
40*0.005=0.2V :this correlates to a 14.2V system.

realistically, that's not too bad. but still, with her ohio generator 160 amp alternator and no capacitor, she is currently at the 14.8V-15.0V range. much better.

earlier i had also mentioned that once the capacitor is drained, it becomes a load on your electrical system and recharging becomes a much larger issue. here are some numbers indicating how big of an issue it can become.

time in seconds = (0.5*FARADs*TARGETVOLTS*VOLTSIN)/Power supply in J/s
we'll assume a 100 amp alternator (roughly the equivalent of most stock alternators) at 14.4 V. that's 1440 watts or joules/second

so,
t=(0.5*1Farad*12.6V*14.4V)/1440
t=0.063 seconds to recharge

what if it's a 40 Farad capacitor?
t=(0.5*40Farads*12.6V*14.4V)/1440
t=2.52 seconds to recharge

what if it's a 40 Farad capacitor and your amp and vehicle are already drawing 95 of your 100 amps?
t=(0.5*40Farads*12.6V*14.4V)/72
t=50.4 seconds to recharge

what happens when there is zero amps available from your alternator? recharge time becomes infinite.

in short, i'm not trying to say that capacitors are useless, but they are being misused and not enough research is being done before purchasing. i find it entertaining that people will spend a month picking out a sub and amp combination and then will throw on which ever capacitor has the most chrome on it.

happy bumping!

 

caps make you cool...thats why i have 2, i'm twice as cool as whoever has 1. simple math

 

Very good explanation. I thought that all caps, from Boss, to PG, were from like only two or three different manufacturers? Or maybe that's the way it used to be...

 

lol word.

but yea, i use capacitors on a case-by-case basis, because most of the time its merely a quick fix. some cars really dont need them.. but awesome cap. novel, Punk0Rama (aka: Neil).

 

It use to be like that.

Great info and you are quite right about anything with a high ESR being esentially useless. Caps can help, but after getting heavily into SPL comps, I learned how a capacitor can be more of a restriction instead of helping. I only recommend BatCaps now or upgrades to the charging system (i.e. Big 3 and/or Alternator)

Alright, To explain how Discharge/Recharge effects the ESR think of it like this:

The Cap can be used for filtering/storage. Sort of like a Water Tower if we look at it like Storage. When a Heavy draw occures at an Amplifier, the Capacitor Discharges. Then it has a Recharge time. This time to recharge will make the capacitor become MORE like a resistor and causes the ESR to Rise. Hence, you observe the figures above.

When you think about this for Bass and Test tones (Basic SPL set-up) it can cause an extremely high draw that'll Discharge the Capacitor faster than normal. We are talking mSec here. Also an SPL system being pushed to the Max will inevitably put it'self into clipping which basically looks like a DC current to the Amplifier and speaker. Very High draw of current and will Immediatly discharge the Capacitor then making it Impossible to recharge itself because the Amp will do it again Very rapidly.

Punk0Rama, You are a man after my own heart. Thanks for bringing something like this to Light. What's your Background? You mentioned a shop.

 

heh, my training thus far has simply been experience and a passion for audio, particularly the perils of car audio. i have actually just graduated from high school about a year and a half ago, and am enrolled in electrical engineering at the local university next year. it's a 4 year course. after completion of that, i intend to go west and do 4 years of acoustical engineering. after all this, i am hoping to take out a sizeable loan and start up my own car audio company. i know, lofty goals, but hopefully one day i can achieve them

in terms of where i have learned things like the above information, it's just a LOT of reading. i am a physics junkie and even while at work, i read whether it be books or just browsing the internet. i have worked for no one but myself (the exception being my current job for cingular) simply because i get the most money that way i do amp, sub, speaker, alternator, battery, and a lot of glass customization (that's how i first got started into car audio.) i did do temp work for a local shop where my job was mostly unique installs involving glassing or designing future products for them, but i quit that due to health problems and because i could make more money by keeping my own ideas to myself, lol.

btw, i love the format of this forum!

 

Oh, BTW welcome to the forum! I'm not like a mega-post ***** or anything, but I just like to pop in and share my knowlege with people ocassionaly. I too used to work in a shop a while ago ('95-'96) and have had car audio as a hobby since then. Again, welcome!

 

it is true only 2 or 3 companies actually still make caps they are all the same except for the covering the reason that no one uses them as much is that for the price of one cap u can add a second battery and never have to worry about having power i would recommend a yellow top optima over any cap

 

a capacitor can be very useful for some things, just misused by many people.

 

In what situations would you consider it useful?

 

a capacitor is good for smoothing voltage ripples. it will give you a more constant voltage rating at the amplifier as during heavy draw the rectification bridge of the alternator is not as efficient. but it still needs to have low ESR. before you ever buy a capacitor, you should ask to see the owner's manual or check it out online to know the ESR rating of that capacitor.
a capacitor (although not the style we're referring to) is also used in crossovers, so that's another good use for it.

 

Adding a second battery can cause more problems than it can help most times. Your alternator still ha to charge both of them. The ESR of a Battery is WAY higher than any cap out there. A second battery is only use full for extreme Draw (SPL) or long listening time.

Non-polarized capacitors are used for Filtering in x-overs and other similar stuff.

 

Out of curiosity, I have a Precision Power 1 farad capacitor that's about 4 years old. Any idea if the ESR is acceptable? They have nothing on their website in reference to their older models, and it was installed by a stereo shop and I never got the manual (long before I knew much about car audio).

 

there is a shop here that is a major dealer for PPI and all DEI products, i'll contact them for you and see what info they have.