capacitors

Discussion in 'General Electronics Chat' started by joshwhitesub, Jan 19, 2010.

1. joshwhitesub Thread Starter New Member

Jan 19, 2010
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Im learning about electronics, but i came across something i dont understand and I hope someone out there can clarify it for me. I've taken apart capacitors before, and i found the two prongs were connected to long plates seperated by oily paper, the two plates never touch otherwise the capacitor would never hold a charge, but if the two plates never touch each other then when you put a cap in line with something like a tweeter to filter the low frequency's how does it still create a loop, the plates never touch, what exactly makes the continuous loop, someone please help

2. retched AAC Fanatic!

Dec 5, 2009
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[ed]Think before you type retched[/ed] Manufactures change the value of the caps by changing whats inbetween the plates or how close they are. The closer, the less power they can fill with before emptying, and the faster they cycle from empty to full and empty again. That is a frequency. With careful selection of caps, you can filter out frequencies due to this trait.

http://en.wikipedia.org/wiki/Capacitor

Last edited: Jan 19, 2010
3. Audioguru New Member

Dec 20, 2007
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A capacitor passes high frequencies like a piece of wire and blocks low frequencies like a resistor. It does not pass DC.

4. joshwhitesub Thread Starter New Member

Jan 19, 2010
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Thank you, that makes alot of sense, i have another question, i dont understand capacitance, if you have a 1 volt 100 micro farad cap, does that mean you have 100 sets of 1 volt

5. Audioguru New Member

Dec 20, 2007
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The lowest voltage rating of a capacitor that I have ever seen is 10V.
A 100uF has a value (its capacitance) of 0.0001 Farads. Its cutoff frequency can be calculated with its load resistance.

6. peranders Well-Known Member

May 21, 2007
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There caps are caps with lower rating than 10 V. 6.3 V is common and for special ones I have seen 3 V also.

7. rvh002@gmail.com Active Member

May 15, 2009
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I suggest you read up on capcitors in the references at the top of this page. A capacitor is also used as an energy storing device. Typically capacitors in the micro-farad range are used for this. Power supplies etc.
Regards

8. joshwhitesub Thread Starter New Member

Jan 19, 2010
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I still dont understand wht the difference between a 10 volt 1uf cap and a 10 volt 100uf, does it hold more current?

9. joshwhitesub Thread Starter New Member

Jan 19, 2010
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I am now confused again on the capacitor, im asking about if you have a red wire going to the positive terminal on a speaker and a black wire going to the positive terminal on the speaker, you have a closed connection so the speaker can work, if you add a capacitor inline with the red wire, you filter out frequencies depending on the cap your using but its still a closed connection so the speaker can still work, but if the plates inside the cap never touch whats the diference between the capacitor in line with the speaker, versus a on and off switch in the off position,

---------red-wire------l l---cap-----------------speaker
-------black-wire-------------------------------speaker
either terminal on the cap never touch so what makes the continuous loop to close the circuit?

10. Audioguru New Member

Dec 20, 2007
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Repeat:
The capacitor passes high frequencies like a piece of wire but blocks low frequencies and does not pass DC.

Some amplifiers have DC at their output that will cause a speaker cone to be pulled in or pushed out causing distortion and maybe damage. A high capacitance capacitor in series with the speaker passes all audio frequencies but blocks the DC.

A tweeter is designed to play only high audio frequencies because it is fragile and low frequencies cause distortion and destroy it. A low capacitance capacitor in series with a tweeter passes high audio frequencies but blocks very low audio frequencies.

11. joshwhitesub Thread Starter New Member

Jan 19, 2010
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I appreciate you being so patient with me, but Im not talking about frequencies i just dont understand how if the plates inside a cap never touch its like a switch on the off position, electricity doesnt pass through the two plates, but when you put one end of a wire(like the speaker example) to one side of the cap,(which does not touch the other, and then take the other wire and put it on the other side of the cap, (again neither plates touch, the that wire goes to the speaker, if they never touch how does the electricity continue from one side to the other, if they never touch, its like hooking something up normal and cutting one of the wires, now the wires arent touching, so it doesnt work, but the caps plates never touch yet in line with something it does work, thats what im trying to understand,

Apr 20, 2004
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13. dsp_redux Active Member

Apr 11, 2009
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I strongly suggest you to read the section on capacitors on this site. A capacitor is defined by $C=\frac{dq}{dv}$ or if you prefer $i(t)=C\frac{dv(t)}{dt}$. I'll try to explain it to you but I don't know how much you know about that stuff yet so I'll go wide. Current is created by charges (electrons) moving in a direction where there are holes for them to go. Holes attracts electrons and vice-versa (+ attracts -). If you put a certain voltage on a capacitor, you'll put lots of holes (+) on the positive side of it. Electrons will be attracted by those charges on the other side of the capacitor. +++++||-------. You can store those charges in the cap. C is the value of the capacitor in Farads (uF stands for micro-Farads). The higher the number, the more charge you can store. Now I don't know if you are familiar with complex numbers? That could simplify the explaination of capacitive/inductive vs purely resistive impedances, related to current and voltage behaviour in a circuit.

14. joshwhitesub Thread Starter New Member

Jan 19, 2010
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Thank you for everyone being patient with me, i understand what your saying but i guess i explained it wrong, i dont understand how if the two plates in a cap never touch what lets electricity to flow through it when its in line with something, because if you take two wires and never touch them together electricity wont go through it cause their not touching but a cap somehow does, in the cheap ass drawing i did above, i know how to charge a cap, i know all that stuff, i just dont understand how if the capacitor is inline with something --------l l-----even the schematic shows they never touch yet electricity can go through them even though there separated by an insulator, this is really hard to explain, without just talking to someone directly person to person, so i appreciate everyone being very patient with me

15. Audioguru New Member

Dec 20, 2007
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The plates on a capacitor are extremely thin so they have a huge surface area to hold many electrons. When a capacitor charges it holds the electrons on one plate and a lack of electrons on the other plate. Therefore an AC signal can charge and discharge the plates a little which causes the signal to pass through.

16. hobbyist Distinguished Member

Aug 10, 2008
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The plates are so close to eachother that allows a charge to be felt across the insulator.

poor example, but a wire broken with a small enough gap between can allow electric charge to flow, such as a spark plug.

Although a capacitor is not any thing like a spark plug, but you get the idea, that if the gap is small enough a charge can accumalate.

17. retched AAC Fanatic!

Dec 5, 2009
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The clouds do not touch the earth, but when enough power in built up in the clouds the electricity jumps to earth. Same concept. The amount of power needed to jump a gap between two conductors changes with the distance between the plates. So, if 100w will jump one inch(For instance) it would take more than 100watts to cross a 1.1inch gap. So a bunch of really smart people found out if you use some material besides air in between the plates, you can change the power needed to jump the gap.

So the same way the clouds keep building a charge until they discharge, a capacitor does the same. It keeps eating power until there is enough to jump that gap.

By using some math you can time the jumps. If you put 12 watts into cap A, it will jump every 5 seconds. if you put 24 watts into cap A it will jump every 2.5 seconds.

(the numbers are way wrong. very wrong)
This should help:
http://www.satcure-focus.com/tutor/page6.htm

18. joshwhitesub Thread Starter New Member

Jan 19, 2010
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Thank you Guys so much, i really understand it now, i've been picking my brain for hours trying to get this, so thanks again

19. BillB3857 Senior Member

Feb 28, 2009
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Last edited by a moderator: Jan 21, 2010