caps - what do they do or what do they supposedly do?

[geolemon 10+ year member]

Well, either way i dont have room for one, so i say screw the cap and i'm just gonna get a bigger alt, new battery, and upgrade the "big 3".

I'd frown on an alternator upgrade for many reasons.

• "upgraded" alternators often don't deliver much more idle-RPM current than stock alternators
  
• "upgraded" alternators inherently rob horsepower, proportional to their increased size, by their larger drag on the motor at all RPM's
  
• alternators are expensive, and possibly not available as a bolt on... rewinding a stock alternator leaves reliability concerns
  
• if you have enough power in your car to actually seem to justify an alternator upgrade, and you can actually stand to be in the vehicle, under those conditions, for time periods long enough to seem to justify an upgrade - the alternator isn't your problem. You need to track down serious inefficiencies in your system.. in other words, you could be (should be) getting more output, with less power.
  
• the money spent on an alternator could be more usefully spent elsewhere.
  

New battery might be nice, and the "magic 3" are always a good idea... but even more fundamental is their connection points.. metal on metal.

Bear in mind what happens when your lights dim. That's no sign of a problem or distress.

The frequency of headlight dimming might be.

But, you'd virtually need to be dimming your headlights for fully 50% of your driving time in the vehicle before you'd reach the point where the battery wasn't fully recharging back to it's full 12v level when you were done operating the vehicle. And that would be the point where you would, legitimately "need" to upgrade the alternator.

I doubt you are at that point.

Obviously I don't know your system or listening styles, but listen to my logic:

• Bear in mind that music is dynamic, and only infrequently does any component of the music reach that maximum recording level - there is headroom.
  
• Music has a "duty cycle" if you will. A bass drum is not a constant tone, but rather something that is only present in the music a certain percentage of the time.
  
• Even given music recorded at the maximum recording level - even using something continuous like test tones recoded at that 0dB reference recording level, your amplifier's output will be proportional to your volume knob. Your amp won't produce max power unless your volume knob is set to maximum output (and therefore the amp won't draw it's maximum current unless your volume is cranked fully)
  
• High decibel levels can be damaging over long periods of time, your volume will more often be set at a tolerable level than a maximum level. If you can truly tolerate the maximum level, there are problems in the design of the system, not the electrical system.

All these factors converge to a point where even a massive, high power system will have an average current draw only somewhere in the 20a-40a range, if even that....despite the ability to draw peak current over 200a even. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Don't have room for a capacitor?

The nice thing about capacitors is that they can be hidden anywhere. Your rear quarterpanels usually have voids in them, as does an entire trunk... all over the place.

With the budget available for an alternator, you should be able to afford even a slick installation to keep it out of your way. It's only a 3" round little thing. They can be tucked away anywhere, they aren't wired in series, after all. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[Phatillusion 5,000+ posts]

I don't know if it's been stated yet since I really didn't feel like completely reading long posts, but if a capacitor stores power, then it must get that power from a source (alt or battery) therefore, how is it helping your system? To me a capacitor is a load. Until I can hear a difference, I would rather spend my $100+ on something else, and I suggest you all do the same.

 

[tommyk90 5,000+ posts]

Well, i have a regular cab s-10, so i KNOW i don't have anywhere to put it. Check out my sounddomain page to see for yourself.

As for dimming, it happens when i am both sitting idle and driving(1500-2500 RPM). But yet the voltmeter stays at 13.9 volts. And for alternators, i can get one from http://www.excessiveamperage.com that puts out its power once the RPM's go up to 900, and once that happens it stays on throughout the RPM range.

And actually, the dimming is worse on kickdrum bass than it is on long, drawn-out notes.

 

[havoc06 10+ year member]

two questions for you geolman. First off, deep cycle batteries are not recommended as system dedicated batteries? Then why do many people use Optima Yellow Tops? Second question. Say i had a 100 Farad Cap, and 5k of power. Would i notice an increase on SPL on the first burp?

 

[maylar 10+ year member]

I don't do "bullshit".I also don't do reading comprehension seminars...

I suggest you revisit my words to see where you went wrong. I never said that electrons flowed slower or faster.

I'm pretty sure I uderstood you... that a battery is slower to respond to a quick change in demand than a capacitor. If that wasn't your point, then please ignore this post.

I said that batteries are slower to respond to discharge, and are also proportionally slower to charge. That's not a function of electron speed.

Capacitors have lightning fast discharge times, and proportionally lightning fast charge times.

I'll give you one large difference (related to their speed, charge and discharge) - ESR.

The internal resistance of a fully charged car battery is on the same order of magnitude as a cap's ESR, maybe a bit higher. But that has nothing to do with how quickly it'll respond to transient currents.

By the virtue of your post above, you seem to think that alternators, batteries, capacitors all do the same job, as sources of electricity. Very interesting.

All three are voltage sources. All can be represented by a Thevenin Equivalent of an open circuit voltage and a series source impedance. At least for transient conditions, which is the case in point. That's what I was taught in EE school.

The first sentence says it all.

To quote that sentence: "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 itself." Whoever wrote that is an idiot. The time it takes to discharge a cap depends on the RC time constant. A battery could last ~hours~ not minutes, but that has nothing to do with how fast it can respond to a transient demand.

So I would take that beer now, except I don't drink (maybe you've had too many yourself). 

Maybe you can shed some of those unedjumicated myths that you cling to (my doubts are that you even understand where they came from - do you? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif).

Too many beers is true. If I came off a bit sarcastic, I apologize.
As to uneducated myths, I've been an EE for 30 years and I know for a fact that batteries have superb "speed" (called transient response). In fact, instrument makers like HP and Keithly make electronic equipment that can simulate batteries, and transient response is a key issue. Read the product description of one of them:

http://www.keithley.com/servlet/Data?id=369

 

[zane 10+ year member]

Uggh.

Another Cap thread.

I have argued this point too many times allready. It will not happen again.

I will only point out that once a cap discharges (lightning fast) it then becomes just another strain on a weakened charging system; thus making them virtually irrelevant.

The alternator has to catch up some time to charge the battery and the cap, plus maintain all car electrical current while doing so.

Cap's are merely a load once discharged and remain as such until the alternator recharges it, after recharging the battery.

An Automotive Charging system does not re-charge anything "lightning fast" once current is down. It takes a little while.....

Batteries and caps alike are dependant upon the alternator, thus making it a arguably better choice in a problem charging system.

As for robbing horsepower... Pshhhhhh! //content.invisioncic.com/y282845/emoticons/satan.gif.9c6a335ed7aeeed3ee273e573f1fcaac.gif

Me done with this thread.

-zane

 

[helotaxi 5,000+ posts]

I will only point out that once a cap discharges (lightning fast) it then becomes just another strain on a weakened charging system; thus making them virtually irrelevant.

Unless you have exceeded the capacity of your alternator for a prolonged period of time, you will not "discharge" the cap. A millisecond musical transient will barely touch the charge stored in a 1F cap.

The alternator has to catch up some time to charge the battery and the cap, plus maintain all car electrical current while doing so.

Cap's are merely a load once discharged and remain as such until the alternator recharges it, after recharging the battery.

You have no concept of the amount of charge stored in a 1F cap do you. A 10ms defecit in current of a 100 amps will not make much of a dent in the charge. Also since the ESR of a cap is less (even if only by a miniscule amount) than that of the battery, it will charge first.

An Automotive Charging system does not re-charge anything "lightning fast" once current is down. It takes a little while.....

Batteries, yes. Caps, no. A battery relies on a chemical reaction to create electrical potential. A cap stores a static charge. When you charge a battery, you are in effect reversing the chemical reaction and that takes time. You can force it to be quicker at the risk of sending the battery thermal and greatly shortening its life. A cap takes whatever current is excess and stores it a quick as it gets it. It is a static charge. It "is" lightning.

Batteries and caps alike are dependant upon the alternator, thus making it a arguably better choice in a problem charging system.

If you are continually running in a current shortage situation, then upgrading the alternator is a must. If, however, you get a bit of headlight dimming when the bass hits at moderate to high volume then a cap MAY help. That being said, if you are an SPL competitor, avoid caps like the plague unless you are running way more alternator than your amps could ever draw. In that case a huge capacitor array MAY stabilize the voltage enough for that one peak that could get you that extra .1 dB you need to win. Not a guarantee by any means though. Running the hell out of a system for 30 sec where you are exceeding the capacity of the alternator the whole time WILL drain the cap and it WILL **** even more current and put you further in the hole. This is especially the case with Street class competitors where there is no alternator and all the current is coming from the battery. If you run a cap in the street class you had better peak your score in the first sec or two of your run cause it won't get any louder as the run continues. Also if you listen to a lot of "music" with continous droning bass, the effect of a cap will be mostly negated by the continous draw.

 

[paikiah 5,000+ posts]

oh please let the madness stop....

to each his own about caps.

I say if you have a healthy electrical system, a cap can in fact compliment it (came to this decision after dealing with HO alts on a personal basis, no EE background whatsoever to speak of, though).

Callme dumb, but do i use a cap? Yes. Why? Cause I bought it a long, long time ago.

Would I buy it now if I didn't own a cap? Yes. Why? cause it eliminates dimming of my lights. I don't know how, why, nor do I care..it works for me in that aspect, so I use it. My voltage drops only with lights on at a very slow changing traffic light.

 

[maylar 10+ year member]

You have no concept of the amount of charge stored in a 1F cap do you. A 10ms defecit in current of a 100 amps will not make much of a dent in the charge.

That's the crux of the matter right there. The formula that relates that is this:
i = C dv/dt

A 1F cap will supply 100 amps for 10msec and lose 1 volt of charge while doing so. And somehow this formula never gets mentioned in the literature that discusses them.

The series resistance (ESR) in a cap also introduces losses. Add another .5 volt for a typical .005 ohm ESR at that 100 amps. Not much, but it's there.

If the transient lasts 50 msec (just one cycle of a 20Hz thump), we're down to 5.5 volts of lost charge + IR. The question becomes then, how much time do you expect the cap to maintain terminal voltage at the amp? If you want to cover for a 1/2 second bass guitar note, 1F ain't gonna cut it.

Of course this ignores the fact that the alternator is sharing the load with the cap. And once the voltage gets dragged down to 12.5 V, the battery also helps. Parallel sources get complicated to evaluate.

Think of the total circuit; alternator, battery, cap, wiring, and load. If the source impedance feeding the amp (mostly alternator impedance) is just 20 milliohms, there'd be a 2 volt drop at the amp, and at your lights. A cap COULD reduce that considerably for a very short time. How much difference that makes depends on the music you listen to.

A far better solution is to reduce the source impedance. Upgrade wires and alternator.

 

[helotaxi 5,000+ posts]

That's the crux of the matter right there. The formula that relates that is this:
i = C dv/dt

A 1F cap will supply 100 amps for 10msec and lose 1 volt of charge while doing so. And somehow this formula never gets mentioned in the literature that discusses them.

If the transient lasts 50 msec (just one cycle of a 20Hz thump), we're down to 5.5 volts of lost charge + IR. The question becomes then, how much time do you expect the cap to maintain terminal voltage at the amp? If you want to cover for a 1/2 second bass guitar note, 1F ain't gonna cut it.

If you are running 100 amps in the hole on your current draw, then duh, you had better be running an upgraded alt. That is around 800-1000 watts (ballpark) of power that you just don't have the electrical system to support. A more likely scenario is 10-15 amps. I used 100 amps in my example as just that, an example, not a real world situation (though I know some people who would try it...). I couldn't remember the formula but I knew someone would.

 

[geolemon 10+ year member]

two questions for you geolman. First off, deep cycle batteries are not recommended as system dedicated batteries? Then why do many people use Optima Yellow Tops? Second question. Say i had a 100 Farad Cap, and 5k of power. Would i notice an increase on SPL on the first burp?

Right... deep cycle batteries would not recommended as dedicated system batteries ...for those who are concerned with the impulse or transient response of the battery to sudden demands for current. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

People use deep cycle batteries because deep cycle batteries can survive being discharged numerous times, without suffering the permanent, non-recoverable damage that sort of abuse would impart on a standard battery.

What you trade off, inherently, is the transient performance of the battery.

The thicker plates in a deep cycle battery gain you durability, but cost you performance.

It's your trade off.... just like one person might select a sports car, while the other selects a pick-up truck. Depends on your priorities... performance, or survivability in the face of abuse?

Personally, I think it's like letting your tank run out of gas...you can monitor voltage, and not abuse your batteries. I'd always choose the red tops.

 

[jlaine 10+ year member]

I'd frown on an alternator upgrade for many reasons.

• "upgraded" alternators often don't deliver much more idle-RPM current than stock alternators
  

 
No, but you are driving the car, are you not?
 
Or do we all sit at idle for 4 hours at a time pegging our system?
 
Therefore that one is flawed and the benefit of a higher output unit is still quite there.
 

[*]"upgraded" alternators inherently rob horsepower, proportional to their increased size, by their larger drag on the motor at all RPM's

 
If you notice the "HP robbing alternator" - you have about 3 squirrels for a engine. I suggest you shoot the car now.
 

[*]alternators are expensive, and possibly not available as a bolt on... rewinding a stock alternator leaves reliability concerns

Nothing about rewinding an alternator equates to reliability issues. If you find someone that actually knows what the hell they are doing - they can do more than just rewind the unit - the life span of the alternator can be greatly extended with a few higher duty parts.
 

[*]if you have enough power in your car to actually seem to justify an alternator upgrade, and you can actually stand to be in the vehicle, under those conditions, for time periods long enough to seem to justify an upgrade - the alternator isn't your problem. You need to track down serious inefficiencies in your system.. in other words, you could be (should be) getting more output, with less power.

 
That's personal opinon - not factual documentation. It's pretty much impossible to turn around and go "my subwoofer is inefficient, there... fixed." The listening habits of people vary quite drastically. Your idea of adequate, is NOT someone elses.
 

[*]the money spent on an alternator could be more usefully spent elsewhere.

Personal opinion only. The advantage of the higher output unit is quite evident, no matter how you'd try to cover it up.

New battery might be nice, and the "magic 3" are always a good idea... but even more fundamental is their connection points.. metal on metal.

If you don't manage to cover all of this before finishing your installation - you shouldn't be installing anything in the first place. Fundamental stepping stones to installation shouldn't be a part of this conversation - as the user should be aware of them already.

Benefits of the alternator?

1. Chances are, you can find one with YOUR case, for a very reasonable price, with a much higher amperage, and a warranty.

2. Permanent solution to a supply problem - less chance of failure of the alternator in the future, because you aren't running the new one balls to the wall all the time.

3. Leaves room for future expansion, if you choose to add onto the system in some way.

Benefits of the cap?

Eh... may get rid of your dimming - may not. Still popped 100 bucks out to install something that is a half-assed attempt at a repair. Not a primary supply device, it's just a storage unit.

 

[geolemon 10+ year member]

I'm pretty sure I uderstood you... that a battery is slower to respond to a quick change in demand than a capacitor. If that wasn't your point, then please ignore this post.[/b]

The internal resistance of a fully charged car battery is on the same order of magnitude as a cap's ESR, maybe a bit higher. But that has nothing to do with how quickly it'll respond to transient currents.

[/b] All three are voltage sources. All can be represented by a Thevenin Equivalent of an open circuit voltage and a series source impedance. At least for transient conditions, which is the case in point. That's what I was taught in EE school.

[/b]

To quote that sentence: "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 itself." Whoever wrote that is an idiot. The time it takes to discharge a cap depends on the RC time constant. A battery could last ~hours~ not minutes, but that has nothing to do with how fast it can respond to a transient demand.

Too many beers is true. If I came off a bit sarcastic, I apologize.

As regards your response to the sites I linked to you, I suppose all the other documents out there stating the same thing are written by misguided, uninformed people also?The R/C car people have no application, their observations are a result of the phase of the moon, like our tides, or just their imagination?

Same goes for people who have installed simple 1F capacitors and have noticed improvements in their headlight dimming (which is a direct reflection of the voltage situation, as I described)?

Warewolves, snake oil, capacitor salespeople? //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

Would you say then, that there is no purpose for a capacitor in a DC circuit?

With respect to that, and also to the questions posed by, how would YOU comment with regard to my (and not just "my", I'd point out) statements above, regarding the trade-offs inherent in deep-cycle batteries, that transient response is slower in deep cycle batteries compared to standard batteries?

And if you would not argue that deep cycle batteries respond (transient response, yes) slower (comparing two theoretical "all other factors being equal" batteries), how could you possibly argue that capacitors do not similarly (meaning due to their different properties) have faster transient response than batteries (or at least different, by virtue of the argument)? //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

The construction of these two products are completely different...

And different in such a way that they store charge differently, and release it differently.

As to uneducated myths, I've been an EE for 30 years and I know for a fact that batteries have superb "speed" (called transient response). In fact, instrument makers like HP and Keithly make electronic equipment that can simulate batteries, and transient response is a key issue. Read the product description of one of them:
http://www.keithley.com/servlet/Data?id=369

This leads up well to Maylar's post..

Maylar... What is my response... I'm sorry that you are an EE and that you arent' familiar with this? //content.invisioncic.com/y282845/emoticons/wow.gif.23d729408e9177caa2a0ed6a2ba6588e.gif seriously... let's discuss it, not make seeminly inaccurate statements and then try to drop a title.

Believe me, I've been in EE myself, I've been in this industry (and others, for the past 10 years even) long enough to know it's integrity that matters... not titles. Plenty of pretenders, and plenty of competence to be found even under different hats. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

You linked me to an electronic gizmo that's not a battery, seems to simulate NiCD batteries, and doesn't have any references to the response speed of a battery in comparison to a capacitor. I'm confused by that.

 

[geolemon 10+ year member]

That's the crux of the matter right there. The formula that relates that is this:
i = C dv/dt

A 1F cap will supply 100 amps for 10msec and lose 1 volt of charge while doing so. And somehow this formula never gets mentioned in the literature that discusses them.

Your math is also not considering the true scenario playing out...

The capacitor will be charged not to 12v, but to 14.4v.

During the transition time, it'll have 2.4v worth of charge to give up.

Also, during this transition time, it's not unassisted.... the battery is coming up to speed with it's charge you aren't factoring that in AT ALL - you are calculating as if the battery were completely missing, a non-contributor.

One factor to consider would be the time element involved in the voltage drop from alternator to battery.

The most important, regardless, would be asking yourself how - if this capacitor being present only gives a small amount of support - how you can justify that having no capacitor would be better... since that would be zero support. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

Possibly your argument justifies higher amounts of capacitance... but not less, not zero. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

I do note that you seem to be a fan of recommending 'alternator upgrades'.

All this talk of performance, and you'd upgrade the alternator? //content.invisioncic.com/y282845/emoticons/wacky.gif.cf4a48f9e6dfe9504ffd2c946fd2f340.gif

The law of conservation of energy states that it can not be created nor destroyed, you know... it has to come from somewhere.

You'd upgrade the alternator, and put a heavier drag on the motor, making it less efficient from both a horsepower (loss of HP) and fuel mileage (loss of gas mileage) ALL the time, so that you might cover some (not all) of the transient peaks, that only occur some of the time? //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

In reality, when all is said and done... even systems boasting 1500w amps on their subs, when in normal operation, will still only draw on average around 15a-40a range - the latter being earbleed listening levels, the sort of thing that might cause permanent hearing damage, and not the sort of average current draw that would justify an alternator upgrade, even for those with little 75a alternators.

The justification vs. the penalties - in terms of short term cost (money spent), value (engine efficiency/HP losses, reliability concerns, actual current supply difference near idle RPM, etc), and long term costs (engine efficiency/HP losses, reliability concerns) just doesn't seem to be there for the average person.

Particularly when (as I mentioned earlier), the apparent "need" for one wouldn't point so clearly at a true need, as much as it would wasted install efficiencies... and with that respect, the 'alternator upgrade' would not be a solution, but a band-aid, or mask of the true problems. //content.invisioncic.com/y282845/emoticons/greedy.gif.5a53e6246569d7ab79867170f3b06629.gif

So with respect to this...

It would make more sense to upgrade your wiring (overkill is always good), upgrade your "magic 3", ensure your install efficiencies are in line (such as enclosure design, since subwoofers make up such a large percentage of the current demand), possibly add a second battery to the rear (non-deep-cycle), and possibly not just install capacitors at the amplifiers, but also underhood.

Even with all this (factoring out expenses that were already present), you still wouldn't have spent nearly the money an alternator would cost, and you'd have an efficient supply system.

And if you got to THIS point, and truly needed an alternator upgrade - then the decision could be made with a clear mind.

However, as I mentioned... if you did truly NEED an alternator upgrade... the alternator upgrade still won't stop your headlight dimming, because you'd be talking about peaks not in the 150a range, but rather in the 200a-250a range or more. //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

 

[havoc06 10+ year member]

geolman, what about my question for spl purposes. Same system with and without caps, will i notice an spl difference on the first burp?