# How do I calculate how long it takes for a capacitor to discharge?

Discussion in 'The Projects Forum' started by Marz Fisch, Dec 26, 2015.

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1. ### Marz Fisch Thread Starter New Member

Dec 26, 2015
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How do I calculate how long it takes for a capacitor to discharge? I want to assemble a chain of capacitors to produce enough electricity to make my circuit run for 2 minutes, and then stop. (120 seconds roughly.) As I understand, this is the cheapest, smallest, simplest way to make a circuit stop after a specified amount of time.

I am new to circuitry, and I am designing a wonderful product for blind dogs. I have found an investor, but he wants me to design the prototype before he pays for the patent.

Any help would be greatly appreciated, I will be posting a handful of other questions regarding the assembly of my prototype circuit.

Marshall

2. ### wayneh Expert

Sep 9, 2010
12,154
3,061
Do you need the capacitors to do anything besides provide a timing function? We really need more info about what you want to happen. There are many ways to time out 2 minutes.

The voltage on a capacitor (or bank of them) depends on the charge it holds: V = Q/C. The charge in turn depends on much current has flowed in or out. You can't make the calculation without knowing the currents, the endpoint voltage you want and so on.

3. ### spinnaker AAC Fanatic!

Oct 29, 2009
4,887
1,017
Before you start asking a lot of basic questions read the textbooks at the top of this forum. It is an excellent text that will answer a lot of those questions.

The discharge rate is based on a number of factors.

To get that kind of discharge duration, you will need a super capacitor. Here is a calculator.

http://www.circuits.dk/calculator_capacitor_discharge.htm

Depending on your power requirements it simply might not able to be done without an enormous cap.

4. ### #12 Expert

Nov 30, 2010
16,345
6,831
I'll work as the designer right after you prove it is patentable, and I believe it will sell, and you sign over 5% of the gross sales to me.

5. ### Marz Fisch Thread Starter New Member

Dec 26, 2015
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It is so humbling to see everyone so willing to help... I am designing a rechargeable dog ball that produces sound for 120 seconds after the tilt switch has been activated, and then stops. I will attach a picture of the circuit diagram I am basing my design around, with only a few minor changes.

Marshall

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6. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
1,440
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If you don't like the answers you can always ask for your money back. Otherwise, take the advice (and your attitude) and learn some basic electronics from the many resources out there. You can't talk about "my design" when you have not and cannot design anything.

7. ### #12 Expert

Nov 30, 2010
16,345
6,831
You need to study up on what is, "patentable".
Some of the exclusions include:
Circuits that don't work.
Circuits that any competent engineer would naturally use for the function that is needed.
Circuits that have been done a thousand times, like a 2 minute timer.

Then again, I saw my neighbor buy a patent for a template you hold against the wall and bang with a hammer to mark where to drill for screws to attach a curtain rod. I have made dozens of templates. So have other people. Only one of them paid thousands of dollars to patent one of his templates. Nobody ever bought a curtain rod hanger template, but he thought he had just joined a very exclusive and elite club.

had an idea, and think you can patent our work.

I don't think so.

8. ### spinnaker AAC Fanatic!

Oct 29, 2009
4,887
1,017

Your dog is going to get awfully frustrated if you have to take the ball away every two minutes so you can charge it. And you are going to get very tired of charging it. A better way to go is to use a battery. If you just want something to make a noise for two minutes than a single capacitor is the wrong way to go. A far better solution would be a 555 timer circuit, assuming you do not need exactly two minutes every time. If so you would need to use more complex timer solutions.

Apr 5, 2008
15,649
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Hello,

Please keep it nice and easy over here.
The members you mention are well respected members over here.

Bertus

10. ### ISB123 Well-Known Member

May 21, 2014
1,239
527
You wont get anywhere with that kind of attitude.