Do you often wonder “how does a capacitor work”? At least I asked myself that many times when I was younger.
I never really liked the “physics explanation”. It states something like “a capacitor works by storing energy electrostatically in an electric field”. I don’t know about you, but that sentence didn’t make me any wiser when I was starting out with electronics.
I like to answer the question of “how does a capacitor work?” by saying that a capacitor works like a tiny rechargeable battery with very very very low capacity.
The time it takes to discharge a capacitor is usually only a split second. And so is the time to recharge it.
What Is A Capacitor?
So the capacitor can store charge. And it can release the charge when needed. But how does it do this? How does a capacitor work on a deeper level?
A capacitor is made up of two metallic plates. With a dielectric material in between the plates.
When you apply a voltage over the two plates, an electric field is created. Positive charge will collect on one plate and negative charge on the other.
And this is what the physicists mean when they say that “a capacitor works by storing energy electrostatically in an electric field”.
There are many different capacitor types.
What Does A Capacitor Do?
A capacitor is commonly used for filtering. But what is filtering?
Battery Analogy
Let’s look at an example with a battery.
Many alarm clocks are powered by the electrical outlet on the wall in a house. Sometimes, the power goes down. Most alarm clocks have a backup battery that will take over and power the alarm clock until the power comes back on so that the time is not reset.
Well, in electronic circuits capacitors can be used in the same way.
Decoupling Capacitors
For example if you have a circuit with a microcontroller running some kind of program. If the voltage for the microcontroller drops for only a split second, the microcontroller restarts. And you don’t want this.
By using a capacitor, the capacitor can supply power for the microcontroller in the split second that the voltage drops so that the microcontroller doesn’t restart. This way it will filter out the “noise” on the power line.
This type of filtering is called “decoupling”. And a capacitor used for that purpose is called a “decoupling capacitor”. It’s also called a “bypass capacitor”.
Using Capacitors For Filters
You can also combine capacitors and resistors to form filters that target specific frequencies. For example in an audio system you can target the high frequencies to remove them (e.g. in a sub-woofer). This is called a low-pass filter.
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Please explain this sentence( I think this is crucial part) “Since it takes some time to charge the capacitor and it takes a bit of time to discharge the capacitor, the effect becomes that the capacitor will resist alternating currents (AC), but let direct currents (DC) pass.”
When the capacitor is charging, current will run through it until it is charged. When it is fully charged, no more current will flow in that direction.
So with DC, a current will flow until the capacitor is charged. Then no more.
But with AC the capacitor gets charged and discharged all the time, so that the current can flow back and forth through the capacitor.
Oyvind
Mr. Oyvind,
Isn’t it capacitors allow AC to pass and blocks DC? I just want to clarify. 🙂
Yep, that is correct 🙂 Connected in series, the capacitor will block DC and let AC pass.
Cheers!
Oyvind
What happens when it is connected in parallel to the ac source?
The capacitor will let AC flow to ground while not affecting the DC voltage except during the initial charge.
You are correct The AC passing is frequency dependent..The DC “seems” to pass only at initial charging.
Thanks a lot Mr. Oyvind for these info. May I ask how can radio reception in a solar home system be rectified. The reception is so bad unlike when connected to the grid. Thanks.
It sounds like the power from the solar system is very noisy. I would suggest creating some kind of filter for it…
Cheers!
Oyvind
Can you give an example of an audio filter circuit that can be used by anybody for free? Math is not my calling 🙂 I just like constructing pre-made circuits, and would like to know what capacitors to use in an audio filtering circuit, cutting frequencies above 15k and below 50hz, Thanks, ifya would, many Thanks indeed 🙂
Hey man!
Check out this document from Texas Instruments: http://www.vyssotski.ch/BasicsOfInstrumentation/FilterDesignIn30Seconds.pdf
Cheers!
Oyvind
Thanks a million dude, exactly what I was looking for. 🙂
No problem man =)
Hey, Hi ! I just want to ask how to select the values of resistor & capacitor to make a low pass, high pass frequency or a band pass filter….i have a enough knowledge of electronics components individually but how to club them together to make a circuit of interest….when to connect which component ?? these questions always get a place in my mind every time….
Hey!
If you want to make a super simple and basic filter you only need one resistor and one capacitor for either a low-pass or high-pass filter.
For a band-pass filter you can connect a low pass and a high-pass filter in cascade.
To select values for the resistor and the capacitor you use the formula: Cut-off Frequency = 1 / (2 * 3.14 * R * C)
So if you have decided on the cut-off frequency and the resistor value, you can find the capacitor value you need by re-arranging the formula above:
C = 1 / (2 * 3.14 * R * frequency)
Does it make sense?
Cheers!
Oyvind
how capacitor works as switch in multivibrator cct
I don’t think it even does work like a switch
thanks for your videos.
i am interested in energy storage. What are the best capacitors able to store and for how long?
Hey Bruce
Here is an article on different capacitor types: http://www.build-electronic-circuits.com/capacitor-types/
The capacitors with the highest storage capacity are called supercapacitors
Cheers!
Oyvind
Mr Admin I need all your e-books for free, can you help me. I would be grateful to you forever.
At the time of writing, it’s possible to get my ebook “Creating Cheap Circuit Boards” for free if you sign up for my newsletter 😉
Oyvind
Dear honorable Dr. Oyvind,
High regards to your good self and commendable efforts in imparting knowledge in others. First, kindly send me your e-book “Creating Cheap Circuit Boards” as a subscriber of your newsletter.
Second, is it possible to have the following books purchased in e-book format; either pdf or other format.
Electronics Concepts and Theory
#1 Getting Started in Electronics by Forrest.M.Mims
#2 Make Electronics – Learning by Discovery by Charles Platt
#3 All New Electronics – Self Teaching Guide by Harry Kybett & Earl Boysen
#4 Practical Electronics for Inventors by Paul Scherz
Best regards.
Nurudeen
Hey, the free ebook is in the first email you recieve after confirming your subscription. Check your spam folder if you can’t find it. The books you are looking for – I recommend you go to amazon.com and see if they have them. I don’t.
Oyvind
Hello Mr Oyfind
I hope that you can help me with my problem say i got a 380 volt or A 220 Volt
generator and this is feeding 380 or 220volt motors
Is there a way that i can use capasitors to cut out volt drop to the motors [in series or parr]?
NB I am not a pro on this please help me
theuns
Hey Theuns
In theory that should work, but you would probably need some really big capacitors. I haven’t worked with those kinds of things, so I would advice you to talk to someone who has done it before.
Cheers!
Oyvind
Hello Oyvind
thank you for all the trouble i will do so
have a nice day
theuns
I have a quick couple of question here. Why a capacitor is used in a ceiling fan? And what is the source to charge a capacitor? Is it AC or DC source?
1. There are so many ways a capacitor could be used in a ceiling fan, so it’s hard ti answer that.
2. Both. But with AC you will also discharge it
Oyvind
Excellent explanation!
The way I think of a capacitor or an inductor is that I think of them as tanks in a water system. A capacitor is a ‘tank’ for voltage. So, if there is less or no voltage in the circuit the capacitor ‘tank’ will supply it until it is completely drained. Similarly, an inductor is a ‘tank’ for current. So, if there is less or no current in the circuit the inductor ‘tank’ will supply it until it is completely drained.
After a water stoppage in a water system, if you are connected directly to the pipe from the water company, you will have water pouring out immediately from the faucet when the water supply is resumed. On the other hand, if you have a tank you will not get water from the faucet until the tank is filled first. The presence of a tank will cause a delay in getting the water out of the faucet after a water stoppage. The addition of a tank may have the advantage of continuous supply in the case of water stoppage but it will also carry with it the phenomenon of delay.
If you carry the example of the tank in the previous paragraph to electric components, the capacitor (which is a voltage ‘tank’) will cause a delay in the presence of voltage in a circuit. The volt will lag as a result and the current will lead. Similarly, the inductor (which is a current ‘tank’) will cause a delay in the presence of current in a circuit. The current will lag as a result and the voltage will lead.
Thanks for adding your understanding as a comment!
Cheers!
Oyvind
I’m working on a project, what is the difference between a Ceramic Capacitor and Electrolytic Capacitor. Pros and Cons of both?
This article was really helpful.
Thank you.
Awesome =)
Oyvind
hi…!!! frd..i could nt how to make any circuit, and cocept..pls help how to understand…still i dnt get clear concept about circuit and devices…can give any idea???
Please go through some theory of basics of electronics and then try to do some mini project on the same…
In my own contribution, I think the answer to the question should have been explain in a plain not by further telling us the meaning of capacitor… course we needed to hw a capacitor works so I think the answer shud have been on how a capacitor works… thank you
If i have a constant supply of say 1V…can i use a capacitor to build up to 9v, then discharge and repeat.i.e. in the analogy of the water tank, a small inlet fills up the tank, which then unloads its volume, then repeats the process. Is there a simple circuit to achieve this
thanks
dingo
Hi, if you apply 1 volt over the capacitor, the capacitor will only have 1 volt.
But you can always create a charge pump: http://en.wikipedia.org/wiki/Charge_pump
Cheers!
Oyvind
Hi Mr. Oyvind, I really like how you explain those stuff. But I need your help. How am I going to explain capacitor with my classmates using cellphone as an example? I need to explain to them in a very simple language I can. I hope you can help me. Thank you
1. Learn how the capacitor works (by reading this article).
2. Figure out some use case in the mobile phone where a capacitor is used, and explain it without using complex words.
Good luck!
Oyvind
Thanks for the explanation.
What are the major types of capacitor
Hey,
http://www.build-electronic-circuits.com/capacitor-types/
Cheers!
Oyvind
eager to know more
How does the capacitor work?
It is possible to discharge when charging in progress?
Or it will only discharge when fully charge?
It can discharge at any time as long as the conditions for discharging are there.
Cheers!
Oyvind
Hello Dr. Oyvind, and thank you so much for sharing your knowledge with us.
I have a question about capacitors.
I am a DIY audio effects builder, mainly to use in my guitar playing. Up to now I simply copied circuits on the net, but I’d like to go a bit further in understanding. My first obstacle is … a capacitor!
I found out that, in the effects I build, the input signal (from my guitar) goes to a capacitor, and from there to the rest of the circuit. Shouldn’t this be insulating the input? What’s the point in putting a capacitor in series with the input, before going to transistors, op amp’s etc.?
Sorry if my question is dumb, a good concept of infinity is my ignorance…
Thank you in advance!
Hey Benagro,
A capacitor in series on the input will only let ac signals through. So if you for example connected a battery directly to the input, it would be ignored by the rest of the circuit.
Cheers!
Oyvind
Hi
I want to know that in the complex circuit -full of component- the capacitor can be used to store charge from man DC battery, then capacitor supply another part of circuit permanently?
i mean when capacitor charged by main DC power can simultaneously supply another circuit or another part?
thanks
Hi,
The capacitor is either charging or discharging. It can’t do both at the same time.
Cheers!
Oyvind
Hi ,nice explanation for capacitors but i don’t understand how the capacitor discharges ,in mostof the circuits we connect the connect capacitor in between the ckt then, how will the electrons collected in positive plate will reach the negative plate when there is no dielectric in between.
For example, yu can connect a battery directly to the capacitor and it will charge pretty fast. To discharge it, connect for example a resistor between the two pins of the capacitor and the electrons will flow through the resistor (or any other electronic circuit).
Cheers!
Oyvind
Do capacitors fail, and how can you test them, or check them???
Hey, yes they do fail. But how to test them I don’t know. Maybe with a multimeter with capacitor measurement function .
what is the uses of capacitor in circuit of heartpace maker , radiation detecting device . electronic filter?
Please
Yes could be. A capacitor is used for many things within one circuit.
Best,
Oyvind
Hi, please could you tell me if there are different types of capacitor that allow for different lengths of time for the discharge of the energy, what I trying very poorly to ask is, can you get some capacitors that will discharge in milliseconds and others that discharge in seconds and if so what is the maximum length of time they can they take to discharge.
Thanks in advance from a very uneducated man
Hey Adam,
Yes you can. The capacitance value of a capacitor will determine this.
Cheers!
Oyvind
Hi
Can u tell me please when to use electrolytic capacitor and when to ceramic(polarityless) capacitor?
Hi, I wrote about that here: http://www.build-electronic-circuits.com/capacitor-types/
Best,
Oyvind
Hi Oyvid
I have had a look and a read of your posts, i am unable to find what im looking for, I have a 47000uf 40 vdc capacitor that is fed from a 24v dc supply, it is used as a smoothing capacitor i believe, it is then in parallel to a set of batteries that are being charged from it and is used to drive a 24v dc motor back and forth, the problem i have is that the capacitor has gone faulty and has increased the output to 36 volts. i need to change the capacitor but unsure if i need the same size or could i use a smaller uf rating?
I take it that the 40v dc is its max working voltage?
Regards
Dave
Hey Dave,
Yes you are right. The 40V is the max voltage.
Best,
Oyvind
Yeh! man I have learnt a lot from the video clip “How to work a capacitor” .
Thank you,
But I have also a curiosity about the question, “Why a capacitor is connected through A.C. supply?”
If your answer is only for smoothing the circuit or about high pass , low pass; please I want to know about high pass and low pass circuit.
If you send your reply to-
[email protected]
I shall by highly grateful to you.
why does the capacitor charges and discharges ”exponentially”
please answer this question
thanks in advance
so You didn’t say why we use capacitors, ?
Hi
I have a dc motor that does not start up sometimes. It is a bidirectional motor that runs in one direction, then stops and then runs in the opposite direction. Sometimes, not always, it wont start running, I have to tap it or give it a turn. I want to put a cap on as a Kick Starter but am not sure of the values. Please assist me:-)
Hi, sorry I have never heard about that method, so I can’t help.
Good luck,
Oyvind
I would be making an educated guess at why caps are used in a ceiling fan and I think it has to do with the use of a dimmer switch on the fan motor / light fixture. Dropping the voltage via a dimmer switch, on light bulbs makes them dim. This is called a potentiometer. If you do the same thing to the fan motor and drop the available voltage, this causes current to go up (voltage and current are inversely proportionate to each other). This in turn will cause the fan motor to hum very loudly and would eventually burn out the fan motors windings. You can install capacitors and resistors into the fan itsef to turn the potntiometer effect into a rheostat effect. Now, the current goes down instead of the voltage and the fan slows silently in cadance with the dimming light kit on the ceiling fan.
Hey oyvind…cant i get a free version of your ebook instead of buying it…
How capacitance is appeared by dielectric?
Great post!
Easy to follow and understand the very basics concepts
Thank you
thanks for the educative lessons yo
u have provided about capacitors.
thank u for this inform.
i have a question.
if a dielectric material is in between the two plates of a capacitor than how current passes through it?
An electric field is created. Read all the details at wikipedia: https://en.wikipedia.org/wiki/Capacitor
Hi Oyvind,
I wish to create an AC to DC converter, 100~240VAC input, 24VDC output & 5A. From electronic book, it mentioned converting from AC to DC by using Full Wave Rectifier, but that cannot fit to what I need. Let say I design a circuit according to input 110VAC and I can get 24VDC output, but when I change the input to 230VAC, the output VDC also vary. Please can you guide me how to create a constant 24VDC output with 5A, regardless of the input supply?
Thanks and appreciated
Ervin Yu
Hey Ervin,
Check out this article for the basic idea:
http://www.build-electronic-circuits.com/power-supply-circuit/
Just replace the voltage regulator with one that gives 24V 5A
Oyvind
How capacitor change the polarity?and why
Hai sir
I have one silly question on capacitor why we use capacitors in AC circuits because with out ac cannot work any ac devices
Clarify me sir plz
In AC circuits capacitors are often used as filters.
How Decoupling capacitor works and it’s applications
How can we made a cellphone jammer by simple components
why are we putting screens with capacitor in a current transformers? how does capacitor divide the voltage or current in a 132kv transformers?
What could be happen when pass minimum volt over the capasitor????
If you put more voltage than the minimum voltage, the capacitor could break.
Best,
Oyvind
heyy oyvind. I tried to put capacitor in my circuit just as u did in ur video but the led still gets off without a delay. Tried it in series and Parallel, can u tell what goes wrong?? The arrangement of components are same as urs in the video!.. On it. Is written 63 v and 1microfarad
Hey Savidh,
1 microfarad is too little to see the delay. In the video I used 2200 microfarad.
Best,
Oyvind
Hi Sir
What If we use a conductive dielectric material in the capacitor for AC supply?
The current that will through it will be the displacement current??
This is such a great explanation on the basics of capacitors.
I really like your video example showing how a capacitor acts as a “local storage” element that will charge up in the presence of a voltage, and will discharge when that voltage is removed. What a great way to illustrate that with a LED.
And of course, given how a capacitor works, it makes total sense to use them for decoupling and filtering.
Thanks for putting this together.
Mike
Great Video, thanks. I am an amature model rocketer getting back into the hobby after a 40 year hiatus and want to build a firing circuit that amplifies the 12v dc energy into a momentary surge or pulse that will ignite multiple engine clusters (if you’re familiar with the hobby) and send the model rocket skyward. Basicly you are heating up nichrome wire with resistance to generate a spark to ignite the propellant in solid fuel model rocket motors. With multiple motors you have a significant voltage drop across the circuit so the possibility of a misfire is high. I figure that if the amperage is boosted with the help of a capacitor this will solve the problem Thanks!
Hey John,
Cool project! You should post a video when you’re ready.
Good luck!
Oyvind
Very Useful …Thank you sir …
if capacitor is in parallel
You did an excellent job of teaching what a capacitor is and how it works. You physical explanation was great and understandable for those of us who are visual learners. It was basic, easy to understand, engaging, with a flawless explanation. You are a good teacher.
Thanks =)
if I connecte a capacitor in series what will it do in a circuit please
If the input is DC, it will behave like a wire without resistance at first (for a few micro- or nanoseconds). Then after a few milliseconds or seconds, it will behave like one side has no connection to the other side.
Best,
Oyvind