capacitor help-- supposed to discharge itself?!?

[CHEMMINS 10+ year member]

yeah... I know that. In fact your estimates of 70-80amps are exactly what I came up with myself (80amps @2000rpm on the alternator, according to the manufacturer... and given 700rpm at hte crank and roughly a 3:1 pulley ratio...)Which is enough to run the fan continuously but not enough to start the fan.

Why wouldn't a cap help with supplying the amperage surge to start the fan?

80 Amps at 2k on the tach mean about 50 at idle. No wonder you are having probs.

 

[05trailblazer 10+ year member]

//content.invisioncic.com/y282845/emoticons/uhoh.gif.c07307dd22ee7e63e22fc8e9c614d1fd.gif just a get a battery

 

[audioholic 5,000+ posts]

Cap threads always lead to people breaking the 'dont go off-topic' rule. Lets get back on-topic and stay there guys. Thanks.

To answer the OP, no, a cap should not discharge itself when there is no load on it. It should hold a charge for months, if not years, given no load to drain it. It may be that you have a bad cap (internal short), or that you are doing something wrong in your testing, its really hard to say for sure through a computer screen.

Yes, caps are used all the time as an auxiliary power source for 'starting' an electric motor. Large electric motors such as those used on large air compressors have them, for example. Its a very common use for a capacitor. But if your cooling fan requires a cap to start properly, you have bigger issues, tbh.

 

[BerniniCaCO3 10+ year member]

Chemmins, reread what I'd written before you're so quick to call me an idiot. 2k ON THE ALTERNATOR. 6" crankshaft pulley. 2" alternator pulley. 700rpm @crank =2100rpm @alt =>80amps.

Thanks audioholic; I might be returning this one then.

Not much could be wrong: charge it with a battery and resistor in series, check voltage with a quality (high-resistance) voltmeter.

My bigger issue is that it's a nonstock setup, crudely implemented.

In the original car that this fan was designed for, the engine computer ran the fan, which presumably, though I don't have inside knowledge of the programming, would enable the designers to slow the spooling of the fan with triodes/diodes/variable resistance of some sort so it didn't draw as much on startup; or simultaneously also bump the engine rpms before triggering the fan. So you don't ever hear of a car which was designed with an electric fan matched to it, stalling out just because the fan turned on

But rather than even attempt to reprogram the computer or somehow hook up a mark viii's ecu just to run my fan, which would rely on several sensors I don't have for it, much easier to put in a capacitor....

I did have a chat with a local audio shop this evening. He said that every capacitor he's ever sold or installed, does seem to drain itself very quickly even wholly unhooked.

I don't think a textbook capacitor should ever do this.

Is it possible these capacitors are being designed with some deliberate safety circuit in mind, to keep from holding a charge while stored off the vehicle, and/or to keep from running the car when some idiot --not knowing there's a capacitor in the trunk-- unhooks the battery and thinks he's safe to go swapping the starter motor and blows the capacitor when he shorts the positive to ground?

 

[BerniniCaCO3 10+ year member]

Figured I'd follow up on this!

I installed the capacitor yesterday,

and, to my great relief, it works perfectly.

Where before every time the fan kicked on, the engine would suddenly buck and rock the car as it stumbled to 200rpm and maybe recovered, maybe didn't; now... nothing, sweet nothing, not a ripple in the idle speed to tell you the fan turned on.

The capacitor seems to provide the current kick just to start the fan; the alternator, and engine, can keep up from there.

In my case I already had a huge battery, and it was already closer to the fan than even the alternator, by maybe 5 feet of wire; so a 2nd battery couldn't have been the answer.

I don't know where capacitors sit in the audio world.

I'm not sure how audio competitions are usually run.

If they're run with the car OFF a capacitor would do no good at all.

If you have an audio competition with the car, and therefore the alternator running, I could see it helping with the heaviest bass notes, so the draw is on the capacitor and not on the alternator. It does seem to have worked a miracle in that fashion with my cooling fan.

But it took a 70amp extra load to seriously affect my engine at idle: I'm not sure how much an amplifier will be drawing just for a bass note, if it's anything like 70amps or not close. If not close, then again, probably a capacitor is a waste.

 

[audioholic 5,000+ posts]

Figured I'd follow up on this!
I installed the capacitor yesterday,

and, to my great relief, it works perfectly.

Where before every time the fan kicked on, the engine would suddenly buck and rock the car as it stumbled to 200rpm and maybe recovered, maybe didn't; now... nothing, sweet nothing, not a ripple in the idle speed to tell you the fan turned on.

The capacitor seems to provide the current kick just to start the fan; the alternator, and engine, can keep up from there.

In my case I already had a huge battery, and it was already closer to the fan than even the alternator, by maybe 5 feet of wire; so a 2nd battery couldn't have been the answer.

I don't know where capacitors sit in the audio world.

I'm not sure how audio competitions are usually run.

If they're run with the car OFF a capacitor would do no good at all.

If you have an audio competition with the car, and therefore the alternator running, I could see it helping with the heaviest bass notes, so the draw is on the capacitor and not on the alternator. It does seem to have worked a miracle in that fashion with my cooling fan.

But it took a 70amp extra load to seriously affect my engine at idle: I'm not sure how much an amplifier will be drawing just for a bass note, if it's anything like 70amps or not close. If not close, then again, probably a capacitor is a waste.

We've discussed caps in a car audio system like 14,000 times before here. The answer is more complex than 'they help' or 'they dont help', but 9 times out of 10 it is true that the money spent on a cap could be put to better use elsewhere in the stereo or even the charging system. Not all caps are alike either.

Some amplifiers can draw hundreds of amps.

 

[BerniniCaCO3 10+ year member]

Hmm.

The fact that it seems like it is that simple... means I'm probably not getting something.

I hadn't meant of course to open a can of worms with a capacitor thread: just wanted to know why it was discharging itself when unhooked. And I'm glad it worked for me, of course; it was a nightmare driving home with a cooling fan that could kill the car.

I could probably waste a ton of time wading through 14,000 threads on capacitors: is there a very good and reliable website you would suggest as a source?

I've got the basics, but I'm curious about the 9/10 times they're not a good choice for the money.

Most of all I'm curious about how an extra battery helps. A larger alternator makes sense if the engine can handle it; mine obviously couldn't handle what was probably almost 90 amps drawn through the alternator while the engine was at idle, and I don't think a larger alternator would have changed that. Only an engine with more torque, or a higher idle speed. Cruising rpms are another story.

Didn't realize amps could draw that much; explains a lot. I only listen to my music in my car, casually, so I've never felt I needed a larger amp or large subwoofer than what I've got (which isn't impressive): I suspect audio competition is another league entirely.

 

[audioholic 5,000+ posts]

Hmm.The fact that it seems like it is that simple... means I'm probably not getting something.

I hadn't meant of course to open a can of worms with a capacitor thread: just wanted to know why it was discharging itself when unhooked. And I'm glad it worked for me, of course; it was a nightmare driving home with a cooling fan that could kill the car.

I could probably waste a ton of time wading through 14,000 threads on capacitors: is there a very good and reliable website you would suggest as a source?

I've got the basics, but I'm curious about the 9/10 times they're not a good choice for the money.

Most of all I'm curious about how an extra battery helps. A larger alternator makes sense if the engine can handle it; mine obviously couldn't handle what was probably almost 90 amps drawn through the alternator while the engine was at idle, and I don't think a larger alternator would have changed that. Only an engine with more torque, or a higher idle speed. Cruising rpms are another story.

Didn't realize amps could draw that much; explains a lot. I only listen to my music in my car, casually, so I've never felt I needed a larger amp or large subwoofer than what I've got (which isn't impressive): I suspect audio competition is another league entirely.

Amps = Watts/Volts. So figuring for (approx) 80% efficiency of the amplifier, you can figure on most amplifiers drawing about 85-90 amps per 1000 watts of output. Even many 'daily driver' systems these days utilize a few thousand watts.

I dont know why your cap discharged itself, it shouldn't. Does the cap have a voltage display? That would drain the cap fairly rapidly once the cap was disconnected from the batt/alt.

External caps are largely misused by the car audio community. And the car audio industry feeds off the basic misunderstanding, to make a buck. A cap, even a relatively large one like a 1farad or more, will discharge very rapidly (given the potential in system voltage drop). Small storage capacity, very rapid discharge rate. So with a car whose stereo grossly overpowers the charging system, the cap will dimply discharge down to the system voltage drop, and remain there until the charging system catches back up and voltage rises again. Since the cap's capacity is so small, and discharge rate is so high, it only provides a benefit to the system, in the form of being a power source, for a fraction of a second. This is why I say most car audio enthusiasts using a cap are using it for the wrong reason, as some sort of bandaide for an over taxed charging system. And the industry is making a buck off of this misconception, they market them as a charging system crutch.

The first person to use an external cap in car audio was Richard Clark. If you dont know who he is, he's a well known engineer, audiophile, car audio SQ previous world title holder, etc. Even Clark agrees that a cap will not help a weak charging system. He placed a cap (an array of smaller ones actually) before his amplifier(s) in his competition SQ car for SQ purposes, not because his alt/batt was insufficient. Richard Clark has very vocal for many years now about his views on the industry taking advantage of his idea, and twisting it into something it never was, to increase their profits.

Caps *can* benefit an audio system in the form of SQ because that rapid discharge rate can help supply an amplifier with current it needs in a more dynamic way than a tradition battery. In other words, as a bass note hits, the cap can discharge power very rapidly to catch that increase in current draw much faster than the batt. This very quick amount of supply power the cap provides will never be any real solution to keeping your battery from going dead (a bandaide for a weak alt), but it can help your charging system be more dynamic in providing the continuously varying power the stereo needs.

Now before anyone runs out and buys a cap because I told them it would improve their SQ, keep some things in mind. IN a system that has a sufficient sized alt, your system voltage may never drop, avoiding the cap from ever really discharging, thereby giving no benefit to the circuit. This is rare, as even 'H.O. alts' usually see some power draw spikes that will force it drop its voltage output, but its certainly possible.

Next point to remember, with a large enough system, by the time you array enough caps to get sufficient capacitance to make any real difference, you've probably added so much resistance to the circuit (caps do possess their own internal resistance) that you've outweighed any benefit you would see from the caps.

Next point, it would take a 'golder ear' to hear any noticeable difference in sound quality a cap would most likely provide, since it would be capable of discharging in fractions of a second. Im confident even Richard Clark would admit he mostly added those caps to his SQ car, all those years ago, simply for 'visual SQ' to appeal to the judges. Judging SQ is, of course, subjective. If a judge sees some fancy new gizmo under the hood that is suppose to make the stereo sound better, a psychosomatic episode tends to occur where that judge thinks it sounds better. This is a common tactic used by SQ competitors clean wiring tends to make a system 'sound' better.

Next point to remember, your amplifier already has an array of 'stiffening capacitors' in its input stage. So, in essence, when you go out and buy an external cap for your amplifier, you are telling yourself that either you know more about amplifier designs and the necessary input capacitance than the person who designed your amplifier, or you are buying it because you regard the amp's quality as not worthy of trusting that it was designed/implemented/built well.Read what Im saying one more time, slowly, and think about what it means... your amplifier already has stiffen caps built in.

Last point, for an insufficient charging system, a cap will make no real improvement. Some people experience less headlight dimming from this, which is possible, but ultimately all power must come from the alt. If the alt doesn't produce more current than you are drawing, the inevitable is a dead battery. There are many factors to consider though, such as how often you run your engine without the stereo being on, how loud you tend to listen to your stereo, and even what type of music you listen to can contribute.

An extra battery helps by adding to the storage capacity in the circuit. When the music is quiet (or the stereo is off altogether), and there is a surplus of power from the alt, it charges the battery. When current demand raises above the ability of the alt, that stored energy in the batt(s) is released to pick up the slack, until the demand decreases to a point that the alt is sufficient again. The more batts you have, the greater time can occur between sufficient alt and insufficient alt periods. But, even a large storage bank of batts requires a surplus of energy from the alt once in a while, or it will eventually go dead as well. So again an extra batt is a poor bandaide for an insufficient alternator. A second batt, presumably in the trunk, also provides a small benefit of having a power nearer to the amplifier(s), to minimize resistance in the supply circuit for those rapid transient spikes.

Music is transient, so the stereo's power demand is also transient (going up and down). Is for this reason that you have to look at power draw from your stereo as an average over time. Most people look at it as an instantaneous snapshot in time (my amplifier draws X amount of current, my alt provides Y amount of current), this type of thinking leads to inherently flawed logic and conclusions. One of which being that external caps will help a weak charging system.

There's tons of information on caps out there on the web. If you want to read from an expert, go to Richard Clark's forum over on carstereo.org (iirc) and read it straight from the horse's mouth. He invented the use of external caps in car audio, he's an electrical engineer, and he doesn't pull any punches to excuse an industry that all but lies to its customers to sell them a product they rarely see any benefit from what so ever.

A good website for basic car audio information is bcae1.com. The page talking about caps is here: http://www.bcae1.com/capacitr.htm

Hope that answered all your questions.

 

[Eraceman]

I am having similar frustrations and think some of the responses are quite hARSH!

I bought a 3 farad lanzar electrolitic cap.

it has voltmeter on it and well I charged it with the supplied resistor and it will sit there for a minute and actually starts discharging immediately within 2 min or so it is flat. directions say to charge before install ok so that makes sense dont want the 12 volts to hit it when cap is at zero

but directions also say to discharge after use when you unimstall. i dont see why you would need to discharge it when it goes to zero within three minutes of power disconnect. also when you change batteries on your car it will go flat then it will get a big spike wheN you connect your battery.

mY REAL CONCERN AND BIG QUESTION IS:

iS THIS CAP DAMAGED OR NO GOOD? i BOUGHT IT ON EBAY OPEN PACKAGE.,

IT WILL CHARGE UP BUT I EXPECTED IT TO HOLD ITS CHARGE LONGER THAN THAT. i HAVE OPENED RADIOS AND STUFF IE COMPUTERS WHICH HAVENT BEEN POWERED FOR DAYS AND GET A HUGE SHOCK.

tHANK YOU FOR ANY HELP

 

[jco1385 5,000+ posts]

Amps = Watts/Volts. So figuring for (approx) 80% efficiency of the amplifier, you can figure on most amplifiers drawing about 85-90 amps per 1000 watts of output. Even many 'daily driver' systems these days utilize a few thousand watts.
I dont know why your cap discharged itself, it shouldn't. Does the cap have a voltage display? That would drain the cap fairly rapidly once the cap was disconnected from the batt/alt.

External caps are largely misused by the car audio community. And the car audio industry feeds off the basic misunderstanding, to make a buck. A cap, even a relatively large one like a 1farad or more, will discharge very rapidly (given the potential in system voltage drop). Small storage capacity, very rapid discharge rate. So with a car whose stereo grossly overpowers the charging system, the cap will dimply discharge down to the system voltage drop, and remain there until the charging system catches back up and voltage rises again. Since the cap's capacity is so small, and discharge rate is so high, it only provides a benefit to the system, in the form of being a power source, for a fraction of a second. This is why I say most car audio enthusiasts using a cap are using it for the wrong reason, as some sort of bandaide for an over taxed charging system. And the industry is making a buck off of this misconception, they market them as a charging system crutch.

The first person to use an external cap in car audio was Richard Clark. If you dont know who he is, he's a well known engineer, audiophile, car audio SQ previous world title holder, etc. Even Clark agrees that a cap will not help a weak charging system. He placed a cap (an array of smaller ones actually) before his amplifier(s) in his competition SQ car for SQ purposes, not because his alt/batt was insufficient. Richard Clark has very vocal for many years now about his views on the industry taking advantage of his idea, and twisting it into something it never was, to increase their profits.

Caps *can* benefit an audio system in the form of SQ because that rapid discharge rate can help supply an amplifier with current it needs in a more dynamic way than a tradition battery. In other words, as a bass note hits, the cap can discharge power very rapidly to catch that increase in current draw much faster than the batt. This very quick amount of supply power the cap provides will never be any real solution to keeping your battery from going dead (a bandaide for a weak alt), but it can help your charging system be more dynamic in providing the continuously varying power the stereo needs.

Now before anyone runs out and buys a cap because I told them it would improve their SQ, keep some things in mind. IN a system that has a sufficient sized alt, your system voltage may never drop, avoiding the cap from ever really discharging, thereby giving no benefit to the circuit. This is rare, as even 'H.O. alts' usually see some power draw spikes that will force it drop its voltage output, but its certainly possible.

Next point to remember, with a large enough system, by the time you array enough caps to get sufficient capacitance to make any real difference, you've probably added so much resistance to the circuit (caps do possess their own internal resistance) that you've outweighed any benefit you would see from the caps.

Next point, it would take a 'golder ear' to hear any noticeable difference in sound quality a cap would most likely provide, since it would be capable of discharging in fractions of a second. Im confident even Richard Clark would admit he mostly added those caps to his SQ car, all those years ago, simply for 'visual SQ' to appeal to the judges. Judging SQ is, of course, subjective. If a judge sees some fancy new gizmo under the hood that is suppose to make the stereo sound better, a psychosomatic episode tends to occur where that judge thinks it sounds better. This is a common tactic used by SQ competitors clean wiring tends to make a system 'sound' better.

Next point to remember, your amplifier already has an array of 'stiffening capacitors' in its input stage. So, in essence, when you go out and buy an external cap for your amplifier, you are telling yourself that either you know more about amplifier designs and the necessary input capacitance than the person who designed your amplifier, or you are buying it because you regard the amp's quality as not worthy of trusting that it was designed/implemented/built well.Read what Im saying one more time, slowly, and think about what it means... your amplifier already has stiffen caps built in.

Last point, for an insufficient charging system, a cap will make no real improvement. Some people experience less headlight dimming from this, which is possible, but ultimately all power must come from the alt. If the alt doesn't produce more current than you are drawing, the inevitable is a dead battery. There are many factors to consider though, such as how often you run your engine without the stereo being on, how loud you tend to listen to your stereo, and even what type of music you listen to can contribute.

An extra battery helps by adding to the storage capacity in the circuit. When the music is quiet (or the stereo is off altogether), and there is a surplus of power from the alt, it charges the battery. When current demand raises above the ability of the alt, that stored energy in the batt(s) is released to pick up the slack, until the demand decreases to a point that the alt is sufficient again. The more batts you have, the greater time can occur between sufficient alt and insufficient alt periods. But, even a large storage bank of batts requires a surplus of energy from the alt once in a while, or it will eventually go dead as well. So again an extra batt is a poor bandaide for an insufficient alternator. A second batt, presumably in the trunk, also provides a small benefit of having a power nearer to the amplifier(s), to minimize resistance in the supply circuit for those rapid transient spikes.

Music is transient, so the stereo's power demand is also transient (going up and down). Is for this reason that you have to look at power draw from your stereo as an average over time. Most people look at it as an instantaneous snapshot in time (my amplifier draws X amount of current, my alt provides Y amount of current), this type of thinking leads to inherently flawed logic and conclusions. One of which being that external caps will help a weak charging system.

There's tons of information on caps out there on the web. If you want to read from an expert, go to Richard Clark's forum over on carstereo.org (iirc) and read it straight from the horse's mouth. He invented the use of external caps in car audio, he's an electrical engineer, and he doesn't pull any punches to excuse an industry that all but lies to its customers to sell them a product they rarely see any benefit from what so ever.

A good website for basic car audio information is bcae1.com. The page talking about caps is here: Capacitor

Hope that answered all your questions.

oh

 

[audioholic 5,000+ posts]

I am having similar frustrations and think some of the responses are quite hARSH!I bought a 3 farad lanzar electrolitic cap.

it has voltmeter on it and well I charged it with the supplied resistor and it will sit there for a minute and actually starts discharging immediately within 2 min or so it is flat. directions say to charge before install ok so that makes sense dont want the 12 volts to hit it when cap is at zero

but directions also say to discharge after use when you unimstall. i dont see why you would need to discharge it when it goes to zero within three minutes of power disconnect. also when you change batteries on your car it will go flat then it will get a big spike wheN you connect your battery.

mY REAL CONCERN AND BIG QUESTION IS:

iS THIS CAP DAMAGED OR NO GOOD? i BOUGHT IT ON EBAY OPEN PACKAGE.,

IT WILL CHARGE UP BUT I EXPECTED IT TO HOLD ITS CHARGE LONGER THAN THAT. i HAVE OPENED RADIOS AND STUFF IE COMPUTERS WHICH HAVENT BEEN POWERED FOR DAYS AND GET A HUGE SHOCK.

tHANK YOU FOR ANY HELP

The voltage gauge consumes power to operate. That is where your cap is losing its charge.