/diy/ - Do It Yourself

>>137451
once a capacitor reached peak charge, it discharges.
if current is removed before the peak is reached, it will slowly release until either it is entirely flat or current is restored.

Hey guys I heard about this cool website called wikipedia.

>>137458
Ohh that makes a lot more sense. So if there's an led on the output end of a capacitor, will it light while the capacitor is charging?

Learn the difference between current and charge. Capacitors don't have and "output end". Get that straightened out and come back and post again.

>>137451 Once it's at full capacity it will release all of it's charge in one big surge.


>>137458 once a capacitor reached peak charge, it discharges.


What you both have wrong is you think a capacitor will AUTOMATICALLY discharge once it has reached capacity. A capacitor can be discharged once at full charge (or any other) , and it will do so very quickly, but its not something that happens on its own.

I've drawn a simple circuit of a capacitor used to boost the power of a solenoid. The power supply can't supply that much current all at once. When the switch is open that current slowly builds up in the capacitor. When the switch is closed the capacitor dumps everything its stored into the solenoid.

There are circuits which will make capacitors automatically discharge when near capacity, they usually rely on a zener diode divider triggering a complimentary transistor pair.

>>137473

>current slowly builds up in the capacitor

come on man. I thought you were trying to help, not confuse.

caps do whatever it takes to keep the voltage the same. Plain and simple. It resists a change from 0 to, say, 5v by storing energy as static. Once at 5v it will hold this indefinitely, if you lower the voltage of the battery, it will discharge some of the built up static to try and maintain 5v across it. It will eventually be charged at just 3v, and if you open the circuit so there is no voltage from the battery, the capacitor will be charged at 3v until it can discharge.

>>137473

>The power supply can't supply that much current all at once

Solenoids resist change in current. I really have no idea what point you are trying to make. If you take away the voltage source after the cap is charged and close the switch then it's just a simple oscillator.

>>137479
There was nothing wrong with my statement. For clarification:

current [from the battery] slowly builds up in the capacitor, [we call stored current charge, Current = charge / time] .

I didn't mean to suggest there was current running across the capacitor.

>>137481
>Once at 5v it will hold this indefinitely

So long as its a text book theoretic capacitor.

Real world caps have some leakage albeit very low. The other thing to consider is real world capacitors have internal resistance and inductance which will be different depending on the style.

>>137486
I said solenoid, not inductor. A solenoid is just a load like a motor. There's no storage of energy in a magnetic field, it goes into pushing a big ferrite core forwards.

wrong, wrong everywhere

>>137495
>no energy stored in magnetic fields
hahahhaa. /sci/ would like to have a word with you

>>137502
Please stop taking my statements out of context. I never stated that magnetic fields do not store energy, I stated that solenoids do not store energy in magnetic fields. A solenoid uses a magnetic field to produce linear motion; the energy of the magnetic field is converted to kinetic, not stored.

>>137488

OK, agree to disagree on that point.

What about "slowly"? The cap becomes fully charged in microseconds.

>>137509
It depends upon the circuit it is part of.

>>137509
The time it takes for the cap to become charged is dependent on its capacity and the current feeding it. I never stated those values so you have no basis for stating it would take microseconds. I would still call microseconds "slowly" given the relative speed of most things in electronic circuits, and to emphasize that a capacitor can discharge faster than it charges.

if I wanted to be totally anal about capacitor charge times I could point out that capacitors never technically reach full capacity because their rate of increase decays exponentially.

>>137511

>Say something confusing and unhelpful
>Somebody points it out
>"No man, consider this completely impractical situation where what I said is true"

You are from /sci/ aren't you.

>>137513
>abrasive greentext
seems like you too are from /sci/

OP forget everything you think you know about capacitors and read wikipedia, allaboutcircuits, or an electronics textbook. From the questions you're asking it sounds like the scattered bits and pieces you've read and heard aren't a sufficient foundation of electronic knowledge.

>>137513
You think we should never say a capacitor charges "slowly" because any situation taking longer than microseconds is a "completely impractical situation ".

I was the one pointing out something confusing and unhelpful. The statement I was replying to was misleading in multiple ways.

>>137515
>From the questions you're asking it sounds like the scattered bits and pieces you've read and heard aren't a sufficient foundation of electronic knowledge.

That's 100% true. All I have to go on is bits and pieces of what people have told me, what I've read in tutorials and what I've learned from my own tinkerings. But how else do you get the information? Just look at how many people can't even agree on this one single component. In order to make a tutorial that everyone can agree on, it has to be some big ass exhausting overly specific long winded clusterfuck of a messy documentation. I just want to know how it functions in the real world so I can properly use it in my own applications and see what it's doing in everyone else's.

>>137538
A capacitor is an elevated water tank(often quite tiny).
A battery is a reserviour with a pump attached.

Most electric circuits and components can be converted to some mechanical counterparts. It might help with visualising a bit.

If you seriously want to start analyzing circuits you'll need to dive into the equations that govern the circuits and this is rather headache inducing not to mention time consuming. It's not just about knowing what a single component do, but what a mixed assembly of serially and parallelly connected components will do together. If you google 'insert_component_name_here tutorial' you usually find some decent introductions to that particular. If you want to see real world circuits you could go to say sparkfun and check the schematics for the products in their catalogue.

>>137538
You get the information from diligent study and slowly developing an almost intuitive understanding.

Capacitors have so many applications that I fear no simple "real world" explanation will help you understand how a capacitor behaves when you encounter it in someone elses circuit. They can be used for signal filters, energy storage, timers, capacitive signal coupling, power filtering, many op-amp configurations, power factor correction, and more.

What do you intend to build? Maybe that would help...

>Capacitor
>Reaching full capacity

Yeah, nah, never happens.

>Hey, I can explain this clearly
>Read thread
>Wrong everywhere, errybody ma

Whelp.

>>137566

It's kinda funny, but the answers always have the same level relative to the OP's. question. If he asks something simple, the answers will be totally idiotic and if he asks something difficult, the answers will be much smarter (but still wrong).

>>137569
I'd like to think that people are just trying to keep it simple if OP seems new to a subject, but I know that people like to jump in to any question they think they can answer, even if it's just slightly beyond their expertise. They mean well, but then they start arguing amongst themselves.

Also
>if he asks something difficult, the answers will be much smarter (but still wrong).
lol

Okay let's just take this nice and slow then.

When a capacitor is close enough to being full does it automatically release it's entire charge in one burst or not?

>>137591
I want you to think of a capacitor like two water tanks with a one-way pressure valve between them. The first tank will fill up until the pressure on the valve is too great. Once it's close to level with the second tank, the pressure will be about the same and the valve will close. The second tank is constantly draining, and the first tank is constantly filling, so this process will keep repeating.

The tanks are always the same size, but you can tweak the size of the inlet and outlet pipes, and how strong the valve is. This way, you can make it so the tank is damn near full before the valve opens, causing a periodic burst, or you can set it up so it flutters open and shut letting water through at a nearly constant but controlled rate.

>>137591
>When a capacitor is close enough to being full does it automatically release it's entire charge in one burst or not?
No.

A capacitor can however unload all it's content a lot faster than a battery due to having lower internal resistance. The same current drain would simply heat and set fire to a battery.

This is why railguns use capacitor banks for power injection.

Most capacitors however have really shitty storage capability, measured in micro-farads. However, supercapacitors have as of late started to appear with capacities ranging up to hundred or more farads, although their operational voltage is usually a lot lower than classical capacitors, so a camera flash is still best powered by a classical capacitor, but if you want your solar powered clock radio to survive the night without sun a supercap is a better choice due to it's total energy storage capacity being higher.

That's only the storage aspect of caps, there's a billion other things they are used for too.

>>137595
If you've followed along so far, I'll explain the analogy.

A capacitor is two metal plates that are separated by some medium called a dielectric. A charge of static electricity will build up on the first plate until it has what is called a high electric potential energy. If you're familiar with potential energy, note that this is a slightly different variable.

In this metaphor, the electric potential energy is the pressure, and the charge is the water. Note that a difference in electrical potential energy is referred to as a voltage.

The dielectric that separates the plates weakly resists charge, making it analogous to the valve. In reality, it's not a one-way deal, but can go back and forth. Anyway, when the electric potential energy builds up enough on the first plate, compared to the second, it will have a high enough voltage to cross the dielectric. It will continue to discharge until the difference is too small to cross that threshold.

So you can get capacitors of different capacity, rated for different voltages. You can control how they discharge by adding resistance to the circuit.

Capacitors are used in timing circuits, but I think they are most useful in electronics, specifically, when they are used to smooth out and regulate voltages. They are also used in AC circuits (because, unlike the water tanks, this goes both ways) to reduce the difference in amplitude by smoothing out the waveform.

Note this only applies to voltages. If you want to smooth out differences in current, you'll need an inductor.

>>137602
The time it takes for a capacitor to charge or discharge depends on its capacitance (C) and the resistance in the line (R). This common configuration is called an RC circuit, and has its own wiki article that you should read.

Is that any clearer?

>>137604
Yeah I think I get it now. It doesn't release all of it's charge in one surge but it can release large amounts of current at a time. So using the same metaphor when you say we can tweak the pressure valve and inlets and outlets, you mean with a different capacitor or something that's done with the amount of voltage you're using or something?

>>137604
And current doesn't need to stop before the capacitor discharges right?

>>137604
If you want to see how the variables interact, and have something to generate graphs, you can use this equation:

V = V0 * e^(-t/RC)

Where V is the voltage of the capacitor, V0 is the voltage the capacitor was charged to, and t is the number of seconds passed. RC is usually compacted into a single variable, s or tau, and will be listed on the datasheet for your capacitor.

Example:
Line voltage is 12V
Capacitor is 1000uF (microfarads)
Resistor is 10kO (kilohms, no omega today)
Therefore the time constant (RC,s,tau) is 1000uF * 10kO = 10s (seconds)

So our equation is:
V = 12 * e^(-t/10)

What's most useful is looking at that e^(-t/10) part, because that tells us how quickly the voltage changes in comparison to where it started.

At 0 seconds, e^(-0/10) = 1, so V = V0 (=12)
At 5 seconds, e^(-5/10) = 0.606, so V = 0.606V0 (=7.28)
At 10 seconds, e^(-1) = 0.367, so V = 0.367V0 (=4.41)

Noticeably, that's roughly a third of the starting voltage. This is a handy estimate, in that it took 10 seconds (our time constant, RC) to drop to a third.

So if RC=10 seconds, it takes
10 seconds to drop to about a third
20 seconds to drop to about a ninth
30 seconds to drop to about a twenty-seventh
and so on. It never quite reaches zero.

>>137608
The standard rules for current applies, in that I=R/V, where V is the voltage from the capacitor.

>>137606
I meant from a battery source and whatever you're trying to power.

>>137606 It doesn't release all of it's charge in one surge but it can release large amounts of current at a time.

I think you're confused about the meaning of time constants. A circuit which allows a capacitor to drain can let it go from completely* charged to completely* discharged in one go; not starting and stopping in between. The drop in charge over time is not a straight line though, its curved. Time constants express the curve: After one time constant the capacitor will have 1/2 it's initial charge. After two time constants the capacitor will have 1/4 it's initial charge. After three time constants the capacitor will have 1/8 it's initial charge.....

>or something that's done with the amount of voltage you're using or something?
What are you even trying to say? The voltage of the charge in a capacitor is the voltage used to push current into it.

>>137615
Last page in my wall of text:

Charging a capacitor works pretty much in reverse of discharging. Just like it drops 2/3 of its voltage after 1 characteristic time (RC), it will gain 2/3 in that same time, and so on:

The equation is V = V0*(1-e^(-t/RC))
Your best best to understand is to build a simple circuit: battery, resistor, capacitor, lightbulb, switch, and back to the battery. Don't use an LED because they don't dim. Or you could use one of those obnoxious buzzers, or a voltmeter, whatever.


Buy a couple of capacitors and resistors so you can swap them out and see how the circuit changes. Try to pair them up so the time constant is large (at least 2 seconds). This is probably the best way to understand, and shouldn't set you back more than $5.

Also, try to do the math involved. Plugging those equations into wolfram alpha and tweaking numbers can give you a pretty good idea about what's happening too.

I'll leave this thread open, but I'll be doing other stuff for a while. I hope I've answered your questions enough to where you can read more about it and have a better grasp on the material.

>>137462

0/10 for being a douche

>>137628
>>137615
>>137606
>>137604
>>137602
>>137601
>>137595
>>137552
>>137552
>>137546
>>137538
>>137515
>>137511
>>137508
>>137495
>>137494
>>137488
>>137486
>>137481
>>137473
pic related

I'm still reading this so you know but there's a lot to take in here so responding will be slow.
Aside from an long overdue thanks, I also want to ask something else. Is there a component you can put in to suddenly lower or increase resistance in a live circuit?
Like say for example if you were to put that part and a capacitor in the same line and drop resistance when the capacitor is discharging would it make for a stronger discharge?

I didn't say it sooner but forgive me for not knowing the lingo. I don't typically have anyone to talk shop with.

>>138686
Part 2/2
And speaking of lingo, going back to the water tank metaphor one more time, if how much 'water' each 'tank' can hold is measured in micro-farads, then what are the water valve, inlets and outlets measured in?

>>138686
>>138693
this is a work safe board you piece of shit

reported

>>138693

Water pressure - voltage.
Water flow rate - current.

>>138698
>implying 4chan = sfw
>implying yulia nova = porn
>calling someone a piece of shit when you're a troll

oh u

>>138686 Is there a component you can put in to suddenly lower or increase resistance in a live circuit?... drop resistance when the capacitor is discharging would it make for a stronger discharge?

You really don't need any component that automatically changes in resistance to make the charge and discharge times of a capacitor different. You rarely will have a capacitor discharge back through whatever is powering it.
> inb4 lrc

Pic related. Two different resistors.

Components which "lower or increase resistance" are called semiconductors. There are many different types.

Wall of text guy here
>>138693
The metaphor isn't perfect so not every piece has a perfect analog, but the pressure difference is the voltage in the capacitor, and the valve is a combination of line resistance and the characteristic of the dielectric (the capacitor's cream filling.)

Basically what you need to know in terms of units:
Capacitance is measured in farads
Resistance is measured in ohms
Voltage is measured in volts
Current is measured in amperes
And that's all that is useful in this situation

>>138686
Regarding your concern that the capacitor isn't discharging fast enough, I think I need to divert this conversation into "What are you /really/ trying to do?"

A lot of threads go like this:
>Want to solve problem A
>Investigate subject
>Minor problem B introduced
>Try to solve
>Go on forum about new problem C

a capacitor can be thought of as a high surface area plate, with an adjacent plate about a half inch away like this
-----I I----
the voltage increases on the incident plate until it finally jumps to the other side. thus giving a high voltage jump.

>>138868

holy shit mega newfag detected

yotsuba normal = nsfw

yotsuba B = sfw

it will discharge pretty much instantly unless you hook it up to a resistor

I'M GOING TO KEEP DOING THIS UNTIL YOU TRIPFAGS LEAVE

I'M GOING TO KEEP DOING THIS UNTIL YOU TRIPFAGS LEAfsfVE