SO how many amps will I get if I charge a ONE FARRAD cap up to 12 volts?

[raspberrypi]

Need to test the balls factor on some parts but by way of scientific method. My brain broke down when converting coulums to zipzaps...
Scariest cap ever!

[Brumby]

To get any sort of answer for that, we would need to know the ESR of the cap.

A better answer would include the maximum rated discharge current.  I'd be looking for this on a datasheet.


With both these bits of data, you can then plug in the load characteristics and start getting some answers.

[andtfoot]

I think the actual current delivered is more determined by the resistance (Ohm's law), based on the voltage and internal resistance of the cap (ESR).

The time this can be sustained for is based on the capacity of the cap.
This seems relevant:
http://electronics.howstuffworks.com/capacitor2.htm
By that, it would be 12 Amp/seconds (12A for 1 second, 6A for 2 seconds, etc)

[BobsURuncle]

The capacitor is holding 12 Coulombs of charge.  The rate of discharge, amps, will depend on the equivalent series resistance of the capacitor and the load it is discharging into.  Discharged into a constant resistive load the current will decrease exponentially as the voltage in the capacitor drops.

[sleemanj]

My capacitor calculations page  may be of assistance
http://sparks.gogo.co.nz/capacitor-formulae.html

[neil t]

Need to test the balls factor on some parts but by way of scientific method. My brain broke down when converting coulums to zipzaps...
Scariest cap ever!

I'm guessing you are looking for instantaneous current, perhaps into a car amplifier or something like that.

[IconicPCB]

BobsURuncle gave you the only sensible response.
Capacitors store charge. They do not store current.

Current is rate of flow of charge.

[mikeselectricstuff]

I = V / R
In this case, V=12 (to start with) R is the effective series resistance of your capacitor plus the resistance of the wiring.
V will reduce as it discharges.

[danadak]

Q = C x V
I = C x dV/dT

I in amps, C in farads, V in volts, T in secs

So you know what C is, what desired dV is (12 volts), and pick
the amount of time you want to charge the cap in, dT.

Conversely use same equations for discharge. Note these equations are
for ideal capacitor, one with no ESR, but good approximation for what
you are doing.

Also discharge only works as a fixed current if the load is a constant
current source. If its resistive use exponential discharge equation.
But keep in mind the current will be a f(t) and will decline exponentially.

https://en.wikipedia.org/wiki/RC_circuit

Regards, Dana.

[Vtile]

You get energy, not amps.

[raspberrypi]

You get energy, not amps.

Are amps not a form of energy? Maybe something was lost in translation.

Basically its a car audio cap "Lightning cap Brand" with one of those LED "charge" gauges on top which I'm guessing changes the perceived ESR? I have one of those Chinese 5V to 7kV DC step up transformer cylinders hooked up to it. The goal is to make a continuous spark (a spark that's at the frequency of the device), verse one spark that I get when two 470 uf caps are hooked up to it. I want to make a jacobs latter. I cant seem to find any technical info on this cap so can we guess what the ESR is approximately? What effect would the charge meter circuit have on the ESR (I know it doesn't change the ESR inside  the cap but won't it be seen on the output?).   

[Brumby]

You get energy, not amps.

Are amps not a form of energy? Maybe something was lost in translation.

In discussions like these, you are going to encounter a mix of 'loosely used' and 'scientifically precise' terms.  This is one example.

Amps is a simple quantity that is measured at a single point in time.  You can create a graph of your amps over time by taking lots and lots of measurements and putting lots and lots of points on a chart.  You can then join the dots to create a continuous graph.

But, the fundamental still applies - Amps are a measure of current at a single point in time.  The amount of energy that is transported is measured/calculated over an interval of time, not a point.

Strictly speaking (and I mean getting into the mathematical definitions), if that point in time is exactly that - a point, then there is no time interval and thus, no energy transported.  It's like taking a snapshot of a ball in the air and asking how much kinetic energy it has.  You can't do it.


This may seem confusing, but you have to understand that there are a lot of members here, with a wide range of experience, background and 'teaching' ability.  Be prepared for these - and if you can work out how to fit all the pieces together, you will not only learn more about the subject - but you will also learn how other people express ideas.  Both of these make future learning far more productive.

[Nerull]

The actual definition of an amp is fairly complicated to explain at a basic level, but essentially it is the number of electrons flowing past a point every second, and is an instantaneous value, like the speed of a car. You can't determine how far a car has driven from just it's speed, and you can't determine the total amount of energy transferred from just amps. You can't even tell how much work those electrons can do from just amps. A capacitor will store a given amount of energy, but that energy could be transferred out of the capacitor in 1/10th of a second, 1 second, 5 minutes, 3 hours, 3 years. Each will give a completely different amount of amps, but the same energy (ignoring losses)

[EEVblog]

You get energy, not amps.

Hook that cap up to any load and you'll get amps all right. Short it out and you'll initially get the 12V/CAPesr and then it will drop from there.
You don't have to care about the energy if you don't want to, but of course it still matters because it's the energy capacity that determines how long it power a given load.

[EEVblog]

Strictly speaking (and I mean getting into the mathematical definitions), if that point in time is exactly that - a point, then there is no time interval and thus, no energy transported. 

There's a term for that, Power.
P=V*I

[Vtile]

Good now energy is talked through. 

For OP, do look up the definitions of Farad unit.

source wikipedia.

[raspberrypi]

You get energy, not amps.

Are amps not a form of energy? Maybe something was lost in translation.

In discussions like these, you are going to encounter a mix of 'loosely used' and 'scientifically precise' terms.  This is one example.

Amps is a simple quantity that is measured at a single point in time.  You can create a graph of your amps over time by taking lots and lots of measurements and putting lots and lots of points on a chart.  You can then join the dots to create a continuous graph.

But, the fundamental still applies - Amps are a measure of current at a single point in time.  The amount of energy that is transported is measured/calculated over an interval of time, not a point.

Strictly speaking (and I mean getting into the mathematical definitions), if that point in time is exactly that - a point, then there is no time interval and thus, no energy transported.  It's like taking a snapshot of a ball in the air and asking how much kinetic energy it has.  You can't do it.


This may seem confusing, but you have to understand that there are a lot of members here, with a wide range of experience, background and 'teaching' ability.  Be prepared for these - and if you can work out how to fit all the pieces together, you will not only learn more about the subject - but you will also learn how other people express ideas.  Both of these make future learning far more productive.

Thats how I think of the Heisenberg uncertainty principle. The quicker your "picture" of an object the more you know its location but the less you know its velocity. Time is a measurement of quantity too. Without time there are no quantities, just probabilities or potentials.

[Ratch]

Need to test the balls factor on some parts but by way of scientific method. My brain broke down when converting coulums to zipzaps...
Scariest cap ever!

Your question does not make sense for the reasons others have already given.  Also, a capacitor does not "charge".  It energizes.  A capacitor energized to 100 volts has the same net charge on it as it did at 0 volts.  For every coulomb of charge added to one plate, one coulomb is deleted from the opposite plate.  Capacitors store energy, not coulombs.

Ratch

[mikerj]

Your question does not make sense for the reasons others have already given.  Also, a capacitor does not "charge".  It energizes.

First time I've ever heard that.  A capacitor stores charge, the action of adding charge is charging and once done it is charged.

[Vtile]

Actually it is spring. 

[Ratch]

Your question does not make sense for the reasons others have already given.  Also, a capacitor does not "charge".  It energizes.

First time I've ever heard that.  A capacitor stores charge, the action of adding charge is charging and once done it is charged.

Well, it's true a cap does not store charge.  When you apply a voltage across a cap, one plate accumulates a charge, and the opposite loses the same amount of charge.  The plates will unbalanced, but the net change of the charge will be zero.  It takes energy to separate the charge on the plates, and energy is what the cap truly stores W=1/2 C E^2.

To say a cap "charges" is using technical slang, which like most slang is not literally true.  Sort of like NASA claiming their astros "walk" in space.  Even if everyone knows what you mean, it is not a correct description and can be confusing and sometimes lead to mistakes.

Ratch

[IconicPCB]

The electron is dead... long live the hole

[Dinsdale]

Zero amps.

[danadak]

Not great at Physics, but is there not an equivalency between charge and potential,
one does not exist without the other. So if we charge a cap we can talk about it having
and equivalent coulomb charge, or potential, they are one and the same as related,
Q = C x V. And we can also talk about the energy stored, and its relationship to charge.

Like matter, E = m x c^2, they are inextricably linked to each other. One can talk
about either, both being correct observations.


Regards, Dana.

[Ratch]

Not great at Physics, but is there not an equivalency between charge and potential,
one does not exist without the other. So if we charge a cap we can talk about it having
and equivalent coulomb charge, or potential, they are one and the same as related,
Q = C x V. And we can also talk about the energy stored, and its relationship to charge.

Like matter, E = m x c^2, they are inextricably linked to each other. One can talk
about either, both being correct observations.


Regards, Dana.

Let me ask a quick question.  When you speak about charging a capacitor, what are you charging it with?  Please don't say coulombs of charge, because I showed previously that applying a voltage across a capacitor does not increase its net charge.  Another question.  What do you define as "potential"?

Ratch