Author Topic: Capacitors  (Read 3444 times)

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Offline gamefreakTopic starter

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Capacitors
« on: March 04, 2007, 05:30:43 PM »
Can someone explain them to me? I know that some are polar and wont work unless placed a certain way, but what i cant figure out is how to discharge them when they are full. I know they work based on the current and that current has something to do with the "force" that the electricity has. But can someone shed some light on my understanding?

So far all i have been able to do with a capacitor is make an LED slowly fade with a 470 uF, 16V capacitor, but it stays faded and the capictor keeps the charge.
« Last Edit: March 04, 2007, 05:55:19 PM by gamefreak »
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Offline ed1380

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Re: Capacitors
« Reply #1 on: March 04, 2007, 07:07:27 PM »
The best way I've found to discharge them is to let some touch the contacts, I don't know how good this will work on smaller ones, but works real well on the big ones. ;D
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Offline gamefreakTopic starter

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Re: Capacitors
« Reply #2 on: March 04, 2007, 07:25:14 PM »
yes but i mean... It wont fade the LED it will keep it on and when i turn off the power the LED will stay on for a little bit before fading off
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Offline 555 timer chip guy

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Re: Capacitors
« Reply #3 on: March 04, 2007, 07:43:58 PM »
A capacitor works gust like a rechargeable battery, you fill them up and then discharge then. Polarized capacitors you can only put in one way positive to positive and negative to negative, and be careful if the current reverses or you put it in backwards the capacitor could explode it has happened to me quite a few times. Unpolarized can go in either way. Are you sher that the voltage is not coming from the rest of the circuit, after the LED fades out and the battery is disconnected test the capacitor for voltage because remember the capacitor fills right up again if the power is still on.l

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Re: Capacitors
« Reply #4 on: March 04, 2007, 08:06:49 PM »
470 uF is a fairly large capacitor and can store quite a lot. what is the resistor value that you have with the LED? just lower that resistor value and the capacitor should discharge faster.

(i use an LED on my high power circuits to safely discharge my capacitors)

Offline gamefreakTopic starter

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Re: Capacitors
« Reply #5 on: March 04, 2007, 08:30:14 PM »
i used a brown black red, so 1k resistor and when i use no resistor the LED flashes once and then nothing happens.....

If i use a 100 resistor then the LED just fades too quickly....


What happens is i turn on the power after i have discharged the capacitor and the LED goes on then fades, after i turn off the power nothing happens and the capacitor stays charges, what im asking is how do i keep the LED lit when i turn it on and keep it lit for a short time after i turn it off, right now it fades into nothing and stays off and the lower the resistance the faster it fades.
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Offline 555 timer chip guy

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Re: Capacitors
« Reply #6 on: March 04, 2007, 08:37:45 PM »
I would use a 220uF capacitor and a 470 ohm resistor that always works for me.

Offline 555 timer chip guy

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Re: Capacitors
« Reply #7 on: March 04, 2007, 08:44:22 PM »
i used a brown black red, so 1k resistor and when i use no resistor the LED flashes once and then nothing happens.....

If i use a 100 resistor then the LED just fades too quickly....


What happens is i turn on the power after i have discharged the capacitor and the LED goes on then fades, after i turn off the power nothing happens and the capacitor stays charges, what im asking is how do i keep the LED lit when i turn it on and keep it lit for a short time after i turn it off, right now it fades into nothing and stays off and the lower the resistance the faster it fades.
when you connected your power sores directly you probably fryed your LED.

Offline gamefreakTopic starter

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Re: Capacitors
« Reply #8 on: March 04, 2007, 08:51:36 PM »
no, the LED still works, and i dont think i have a 220 uF, i have a 22 uF, and about 6 10 uF,

But i dont get how i can make the LED stay on and then fade when i turn off the power, it fades when i give it power and then i have to discharge the capicitor myself.

I cant figure out how to make it stay on and then fade when i disconnect power....
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Offline ed1380

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Re: Capacitors
« Reply #9 on: March 04, 2007, 08:59:50 PM »
I'm no EE, but this is how i think it should work. I remember doing it like this about 6 years ago, when I got my first electrical kit
« Last Edit: March 04, 2007, 09:00:35 PM by ed1380 »
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Offline gamefreakTopic starter

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Re: Capacitors
« Reply #10 on: March 04, 2007, 09:24:10 PM »
'ey it worked, thanks
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Re: Capacitors
« Reply #11 on: March 05, 2007, 10:30:48 AM »
it sounded like you had the cap in series with the LED (when the cap should have been in between power and ground) :P
was that the problem?

Offline gamefreakTopic starter

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Re: Capacitors
« Reply #12 on: March 05, 2007, 04:16:49 PM »
yep
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