Hi, in my project I need to use a capacitor to collect Electricity & then, discharge it slowly, so that other devices doesn't get fried. Is it possible?
My thinking is that if I use resistors it'll work. But which resistor to use? I haven't yet decided about the capacitor. So it'll be really helpful if someone can give me a chat or something like that(formula) to calculate the resistor specification.

Thank you all.

 

How slow is slow? How much energy?

In some applications 1 ms is really slow while in others 1 day is really fast.

Since we aren't mind readers....

How is it that you imagine these other devices are going to get fried?

What kind of devices are you talking about?

What kind of voltage and current do these devices need?

What kind of voltage and current can these devices tolerate?

As given, your question would be like me asking how much propellant to use because I am designing a rocket.

What kind of project is this? Related in any way to school work?

 

A capacitor will discharge through a conductor. U know that. It'll also, of course discharge through a resistive conductor.

The energy contained in your cap is measured in Farads, not watts, because it is capacitance, not power. Discharging it will be moving energy, so that will be power. We typically refer to, or think of, power as VA, or volt-amperes. We use Ohms law to calculate the elements of such circuits. It is: E=IR where E represents Volts, I represents Amperes, and I'll let you guess R.

As your capacitor discharges through a fixed resistor it's voltage will drop, and current drop proportionately, not logarithmically, but not directly either. We know that lower current, obtained by either higher resistance or lower voltage, will result in a slower discharge of the capacitor.

We obviously need values to make these calculations. You must either select or measure the values.

At this point, I myself would go Googling to find the formulas which would answer your time questions.

 

Thank you for the info.

 

How slow is slow?
Slow like 1 minute.
What kind of devices are you talking about?
LED, DC motor.

What kind of voltage and current do these devices need?
10 V &1A
What kind of voltage and current can these devices tolerate?
10V
Related in any way to school work?
Science Fair Project.

How can I choose the resistors?

 

How slow is slow?
Slow like 1 minute.
What kind of devices are you talking about?
LED, DC motor.

What kind of voltage and current do these devices need?
10 V &1A
What kind of voltage and current can these devices tolerate?
10V
Related in any way to school work?
Science Fair Project.

How can I choose the resistors?

Based on just these numbers, you need to look for an entirely different approach.

Let's say that you want a capacitor that can supply 1 A for 1 minute while having it's voltage drop from 10 V to 9 V over that time. That would be a 60 farad capacitor. Capacitors that large with sufficiently low series resistance are not going to come your way cheaply.

 

Could one use diode leakage current to discharge a cap?

 

The energy contained in your cap is measured in Farads

Not to be confrontational but is that true? I have always been under the idea that the energy stored in a capacitor was measured in "Joules"?

 

This might help -

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html#c2


Regards, Dana.

 

Not to be confrontational but is that true? I have always been under the idea that the energy stored in a capacitor was measured in "Joules"?

A 'FARAD' is a unit of capacitance. A 'FARADAY' is a measure of charge:

The Faraday constant represents the amount of electric charge carried by one mole, or Avogadro's number, of electrons.

1 Faraday / second = 96 485.3329 amperes

 

Could one use diode leakage current to discharge a cap?

What diodes have leakage currents of 1 A?

They probably exist, but are also probably outrageously expensive because of the enormous forward current they are rated for.

Even if that weren't the case, leakage current would be very unreliable because it is usually minimized and generally only has a max and perhaps a typical spec.

 

Not to be confrontational but is that true? I have always been under the idea that the energy stored in a capacitor was measured in "Joules"?

Your question is a good one, and in fact my prior remark is not absolutely, technically factual.

Stored electrical energy can be quantified using different units. Wiki almost certainly goes into better detail than I, and there's a VERY good set of "lessons" covering electrical theory, measurement, calculations, application here on this site. My point was a bit of how your capacitor will discharge (once charged) and how all the values including time and rate of discharge are variable and related.

 

You are better to use $2.00 rechargeable cells. You can get more FARADAYS out them than you will ever want.

 

Not to be confrontational but is that true? I have always been under the idea that the energy stored in a capacitor was measured in "Joules"?

Joules relates to voltage and capacitance. More voltage or more capacitance = more energy. It is kind of like amp hours vs watt hours. Here is a good calculator for finding the energy in joules.
http://mustcalculate.com/electronics/capacitorenergy.php?v=2.7&c=500

 

You are better to use $2.00 rechargeable cells. You can get more FARADAYS out them than you will ever want.

Agreed. Here are the pros and cons of supercaps instead of batteries:
Supercap pros:
-much lower ESR, meaning you can literally 100s of amps out of them, and charge them a lot quicker too. The ESR is generally a few milliohms as opposed to a few 100 milliohms. Some batteries are better, and some supercaps worse, but you will not find batteries that can output as much power as supercaps for a given size. Due to the low ESR, even when supplying 100s of amps, very little power is dissapated across the capacitor. They are often used to weld because of these properties.
-MUCH longer lifetime, 1 million charge/discharge cycles.
-complex charge and protection circuits are not needed, but often you will want to monitor charge and discharge.

Supercap cons:
-scams involving people selling supercaps
-much lower capacity for a given size. A 500f 2.7V capacitor is commonly 1.5 inch by 3 inch (D by H). An aa battery is typically 1.5V and 6000f. Obviously an AA battery is much smaller.
-they can be more expensive.

So for energy storage, supercaps lose to batteries. There are also combinations of supercaps and batteries for certain appliactions that I will not go into unless you are really interested.