# Supercapacitor and LED help

Discussion in 'General Electronics Chat' started by Lolgogo, Aug 16, 2013.

1. ### Lolgogo Thread Starter New Member

Aug 16, 2013
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0
Hello... This is my first post in this forum.
I am planning to power many (perhaps 16?) leds rated at 2.2volts 24ma.
However, I ran into trouble trying to use my two 2.6v 60 farad supercapacitors.
I believe supercapacitors' voltage drops quickly...
How can I use them to power my leds until the caps have no juice left?

2. ### LDC3 Active Member

Apr 27, 2013
920
160
How about you showing us what you are doing by providing a circuit? All our crystal balls are in use by the Midtown Bowling League.

3. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
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I don't have an exact plan yet and the idea is quite simple. Do you really need a circuit?

4. ### poopscoop Member

Dec 12, 2012
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This wont work well at all. Assuming you charge those capacitors to the max rated voltage, which isn't generally recommended, you have .4 volts of "drop" before the LED's stop conducting.

I can't do the math for how much current you can get from 60(?!) farads and .4 volts, but I don't imagine it's much.

You can make a "joule thief" circuit, but there are better uses of your time. Like batteries...

5. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
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Well, if I connected the caps in series, I would be able to get 5.2volts 30farads. If I used the right value of the resistor, then wouldn't it work? The part I'm concerned about is when it falls below the 5volts. Wouldn't the leds be underpowered?

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Have you considered a joule thief?

7. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
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Can a joule thief put out a consistent voltage regardless of the input voltage?

8. ### #12 Expert

Nov 30, 2010
16,685
7,327
Pretty much, that is the point of a joule thief. It puts out constant current until the battery (or supercap) is sucked dry. (LEDs like constant current.)

9. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
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Thanks for the replies...
So here is a n00by question... Will the output voltage of the joule thief be the same if I put in something like 0.5v to 2. 5v? Will I we require a resistor for the leds?

10. ### #12 Expert

Nov 30, 2010
16,685
7,327
No, the output voltage won't be the same, the current will. The joule thief is a current generator, and LEDs like constant current.

11. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
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Hmm... So if I make the output voltage of the joule thief, say 5volts, can I safely hook it up to an led?

12. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
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Hmm.. So let's say the output voltage of my thief is 4 volts. Can I safely connect it to the led?

13. ### Lolgogo Thread Starter New Member

Aug 16, 2013
11
0
Oops, thought that reply wasn't posted...

14. ### MrChips Moderator

Oct 2, 2009
12,635
3,453
You want to avoid putting resistors in series to reduce the voltage because that would be wasting energy as heat.

15. ### #12 Expert

Nov 30, 2010
16,685
7,327
Let me re-phrase the question.

If I use a joule thief to generate the proper amount of current and voltage for my LED, do I need to put a resistor in series with the proper current to make it something else?

No.