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Capacitor Myth

64K views 145 replies 56 participants last post by  tomtomjr 
#1 ·
Could we have something in here explaining this issue?
 
#3 ·
capacitor | eHow Search

What Is an Electrical Capacitor?

By Paul Dohrman, eHow Contributor

An electrical capacitor is a device on which a charge collects. The usual shape is two metallic plates parallel to each other but touching only two terminal ends of a circuit wire, not each other. Electrons flow from one plate through the electrical circuit and to the other plate, due to the electromotive force of a battery or other source of energy. The charges on each plate are equal and opposite in polarity. The plates are therefore attractive.

Storage of Energy

1. Because the battery, or some other source of electromotive force, displaces electrons from one plate of the capacitor to another, energy is built up and stored in the capacitor. The circuit wires could be removed, and the charge difference between the plates would remain. The energy stored in the capacitor equals the energy required to keep the two plates apart, opposing their Coulomb attraction (an attraction due to their electrical charge). If the plates were not held in place, they would attract each other, make contact, and discharge.

Discharge

2. A voltage can be discharged by placing a piece of metal between the two plates, making contact with both. The excess electrons of the negatively charged plate would then rush over to the other plate, thus removing the excess negative charge on one plate, and the excess positive charge on the other.

Charge Accumulation

3. Charge accumulation is not absolute. That is, it does not stop until the capacitor is detached from the circuit. This is because getting the capacitor's voltage (due to the accumulation of charge) any proportion closer to the final voltage takes a finite amount of time. The voltage building up between the plates therefore has an asymptotic shape, when graphed against time.

In Alternating Currents

4. When the power source supplies an alternating current, the capacitor alternates charge polarity along with the circuit. Electrons falling onto one plate are then pulled off and sent to the other plate, and so on, each time the power source switches polarity.

Use in Electronic Products

5. Capacitors can be used for pulsed power, upon discharge of the charge on the capacitor plates. Pulsed power is useful when sudden bursts of energy are required, e.g. in a laser, or a linear accelerator.

Capacitors, after charging, can be used like a second battery, when the primary battery is being recharged. This is particularly important when vital memory is involved.

Capacitors can be used to smooth out fluctuations in power supply inside electronic equipment.

Capacitors are also used as noise filters, radio tuners, in amplifiers, and in numerous other devices.
 
#4 ·
A capacitor is NOT a substitute for an inadequate electrical system. It takes power (current) to make power (watts) and most of the smaller capacitors will drain faster than one can blink their eyes.

The larger capacitors, 40 farads or more, have been alleged to help in some situations. Unfortunately, at that pricing point, one would be better off purchasing a second "new technology" fast discharge battery.
 
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#5 ·
+1 ChrisB. Figured this would be a good subject for this section.

Rich
 
#9 ·
I use an Alumapro Carbon 15 farad and I will swear by it. i had light dimming issues and once added these symptoms went away completely. Not to mention that this does my power and ground distribution nicely. I do agree however that most caps are a bandaid. I used to have a Stinger 1 farad capacitor and it wasn't very effective.
 
#138 ·
Knowing that your cars alternator was designed to have somewhere around 30% or so of reserve power, how much reserve power does your alternator have versus what your amp is trying to draw? If your amp is asking for more than the reserve, then that is why your lights are dimming. The cap will only mask the real issue. Caps were not made to fix light dimming issues. I believe they were made for competition settings to store energy to get the most out of that first bass drop.

Its usually recommended to first upgrade your wiring between alternator and battery if you are having light dimming issues. Even look at adding additional grounds in your system. Only after that would you look at replacing your existing battery if the problem still persists. A battery that was designed to handle additional load. Only after these steps would you look at replacing the alternator. And you don't have to replace it. There are places where you can have your existing alternator respun for additional amperage.

Now with that being said, I am curious to know what amp and sub you have that were causing these issues?
 
#10 ·
So you replaced a weak bandaid by a strong one?

If you "need" a 15Farad capacitor to prevent the lights from dimming, you *need* a better battery and alternator!
 
#13 ·
I have an Optima yellow top and stock BMW alternator. I'm an Industrial/Commercial electrician with 20+ years experience... I know how power is stored and discharged. The Alumapro isn't your average "bandaid". You say I "need" an extra battery and alternator? thats your opinion. My solution worked perfectly for me. Thanks for your opinion.:)
 
#12 ·
One possible use >>>>

Energy storage

A capacitor can store electric energy.
In car audio systems, large capacitors store energy for the amplifier to use on demand. Also for a flash tube a capacitor is used to hold the high voltage.
[edit] Pulsed power and weapons

Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor banks) are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle accelerators.

Large capacitor banks (reservoir) are used as energy sources for the exploding-bridgewire detonators or slapper detonators in nuclear weapons and other specialty weapons. Experimental work is under way using banks of capacitors as power sources for electromagnetic armour and electromagnetic railguns and coilguns.

Power conditioning
A 10,000 microfarad capacitor in a TRM-800 amplifier

Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage.

Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the lead-acid car battery.
I've looked for articles on capacitors used as energy draining devices , couldn't find any .

Can one of you enter one in WIKI ....
 
#14 ·
If you know how power is stored and discharged, you also know that a capacitor only catches up the peaks in the current-demand (but most amps already have capacitors inside to do this), but raises the constant current-demand.

The only difference is: without a capacitor, you're kicking your alternator and battery untill it finally dies and with a capacitor, you're letting it die a slow and painfull death.

I'm pretty sure your alternator will die one day (probably taking the battery with it) and I'd recommend you to get an upgraded one + a better battery (an Optima Yellow Top isn't exactly the finest quality, it's just well known...) and then try out the install without the 15F capacitor in between.
I'm sure the lights won't dim anymore and as long as the battery is fine or you replace it in time, and you don't add power to the system, the upgraded alternator will last untill the carbon-brushes are worn out.

Isabelle
 
#15 ·
Yes... I understand that a capacitor "catches up" the peaks. and yes it does raise the constant current demand. But if your new constant current demand is within acceptable/safe limits your alternator and battery will be fine. I've considered a second battery but the real estate taken up is not something I want to part with. I appreciate your advice, thank you :)
 
#18 · (Edited)
I am a UNION electrician and proud of it. trained in not only AC but DC.. as well as complex motor controls, relays, etc,... I know what i'm doing. i don't need to defend what I know to 24 and 25 year old kids. I was trying to be civil and polite to you by simply responding. try doing the same.

ps.. I also have a degree in electrical engineering from The university of California, Berkeley but I chose to work in the field since sitting behind a desk doing CAD drawings bores the **** out of me. I am also an Electrical contractor. thanks again for your opinions... I will consider them when doing my install.
 
#23 · (Edited)
FartinInTheTub, very impressive !!

My father-in-law was doing the programming of machines,{EPROMS}, at a company that made automotive firewalls and such , [ subcontractor], when he passed.

Worked for Edison Electric for years ,{ his home was a centennial }, sponsored by Edison.

He had numerous accomplishments and Titles in his time.

His barn was loaded with a variety of electrical parts leftover from his business.

He was District D-2 governor for The Lions Club.

He seemed to think of a capacitor as being beneficial in certain applications , based on his limited experience !
 
#27 ·
Capacitors have some great uses.

Capacitors are NOT for letting you put in a "bigger system". Capacitors do not give you more energy. Capacitors will not give you more "watts".

A Capacitor is great for allowing a 4 channel amp to have instant access to all the power it needs, and for cleaning up the power generated by your alternator. Capacitors are also nice for helping to negate light dimming from using your windows, etc. while listening to your music. A big capacitor can be a good thing, and when used as a SUPPLEMENT, its a valuable piece of equipment.

If your amp pulls 200A and your car only has a 110A alternator, a cap will not help you. In fact, it might make your problem worse. If your car has an ailing alternator, and you have recently started to get light dimming from it, a capacitor will not help you and will help kill your alternator faster.

As an aside, I'm an EE here too. Wish i could get a nice internship at a power utility, I'd love to get a job in a power plant. Nice stable and high paying work there.

I couldn't imagine going through EE school to just be an electrician. The money's just not in the same league, and it's a whole lot of time spent for no reason. I can understand wanting to be more hands on (I'm the same way), but man, I just don't think I could make that same decision. EE is 5 years pretty much country wide now, that's a lot of time to get into something that's not what you graduated in.
 
#28 · (Edited)
Actually the money is there if you are motivated. My Union Wireman make an average of $75k/yr. As a contractor/owner I pull in after overhead/expenses between 200k and 250k. I could NEVER make that working strictly as an EE. And with my degree and experience I don't have to hire EEs to design for me. It's a win win for me and I get to truly enjoy my work and get out in the dirt with my boys.

PS:

"Just an Electrician" isn't a very nice thing to say. The IBEW Union apprenticeship is 5 years of school and 8000 hrs of OJT just to qualify to take your Journeyman exam. I did the entire 5 years of apprenticeship as well as my time at Berkeley. IBEW Union wireman are some of the best trained Commercial/Industrial Electricians in the world. 300+ apply every yr just for the opportunity to enter the apprenticeship... maybe 20-25 a year are let in. So being "Just and electrician" is an understatement in my opinion. :)
 
#33 ·
I'm gonna replace my battery with these. :p

Actually, I'm poking fun now, but honestly 15 years ago people would have poked fun at people wanting to use LEDs for lighting. Nobody's laughing now, it's actually cutting edge and a very real future technology.
 
#39 ·
You know, I've always thought this is weird. Why do they have 1 farad capacitors that are about the size of that thing or smaller, that thing which claims 3000 farads at that size, but most 1 farad capacitors in cars are the size for a thermos? Just because people think the bigger they are the better they must be?
 
#42 ·
lol. I was actually thinking they would have a tiny 1 farad capacitor inside of it, like the little 1 farad capacitors one might see in a physics class, then just a bunch of padding. I wish I could tell what that stuff is, it looks like just some foam insulation mostly.
 
#44 ·
On a positive note about capacitors... In 1997, I had a 1996 Thunderbird with an impossible to solve noise issue. I tried everything I could think of and three different shops tried all sorts of things, but nothing worked. I called a buddy of mine who was out in California in the service and he told me to try a capacitor because it helped a noise issue in his truck. I installed a 1/2 farad capacitor and it filtered out the power line generated noise that no one else could solve.
 
#45 ·
Caps are indeed great for that. That's exactly why they are used in power supplies: smoothing the power signal.
A capacitor reacts a lot faster than a battery and especially older amps can't handle a seriously soiled power signal on their own, so adding a cap right in front of the amp(s) is the best way to clean the power signal up before it enters the amp.

The only reason why a cap also helps light-dimming issues is because it keeps the voltage as stable as possible, not only when the power coming from the battery/alternator is soiled, but also when an amp pulls the voltage down by asking more current than the load-system can handle.
The problem is a capacitor is actually too fast to do this. It will catch up the peak in the current demand, but it will recharge to 99.999% (a capacitor is never 100% full) as fast as it can, causing probably an even higher current-demand on the load-system and eventually drain itself and the battery, and kill the alternator when you play dynamic music at high volume level for a long time.
A bigger capacitor will only stretch this process.

An extra battery will also try to keep the voltage stable and catch up peaks in the current demand, but will recharge slower, causing less drain on the load-system.
Yes, this will eventually drain the load-system and maybe even kill it too if the extra battery has to catch up every single peak all the time, but that's why you have to start with a strong enough alternator and power wiring!


So:
- A capacitor is great for reducing distortion on the power signal, but NOT for dimming lights, whatever the size of it (smaller capacitors are even better in doing what they're designed for!!!), and now even the most critical people know and understand why!
- The only solution for dimming lights is upgrading power wires, alternator and battery-bank. It isn't called the BIG 3 for nothing!

/thread

Now can somebody make a permanent sticky of this that won't get lost when somebody messes with the forums again?

Isabelle
 
#46 ·
but it will recharge as fast as it can, causing probably an even higher current-demand on the load-system and eventually drain itself and the battery, and kill the alternator when you play dynamic music at high volume level for a long time.
This is where I have doubts. I do believe a capacitor will only replenish itself as fast as the circuit will allow it to. Just like an accumulator, it can only take what is available. Since it uses no power of its own (except for maybe a little dissipated in the form of heat), it will not consume any energy; therefore not putting any extra load on a circuit.
 
#51 ·
Caps work depending on what you want to fix. You can't use a screwdriver to use a nail, and you can't use a hammer to put in a screw. Different tools for different jobs.

The problem with a cap is not only that its fairly lossy, it also will charge and discharge more. Think of it this way, say you have no cap and your amp pulls enough power to drop you down to 12V from 14.4V, Your lights will dim but after the bass hit its over. If you have a cap, you may only drop to 12.2V or something, but then after the hit the electrical system must recharge the cap up to 14.4V, causing extra strain. Now imagine you're doing this on a weakened alternator that is already too small to power your system. The extra strain of having to charge and recharge the cap, as well as power everything will cause your alternator to die a premature death.

Capacitors can be made in different ways, many of the "super caps" are constructed in a different way than your normal caps. The normal caps you see are basically scaled up versions of the ones you would find inside your amps, they're considered to be better for signal transmission, and easier and cheaper to make. Things like the BatCap and the Soundsstream and other big caps are constructed in a different way that allows them to hold more energy.
 
#52 ·
Excellent job all! This explanation of a highly debated subject is perfect for this section. It is also why this forum is so valuable to all.

Thanks everyone who contributed.

Rich
 
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