# Supercapacitor set-up

Discussion in 'The Projects Forum' started by tgauss, Mar 11, 2013.

1. ### tgauss Thread Starter New Member

Mar 11, 2013
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I am a total electronics newb and was told this is place to come for genius advice.

I need to make a contraption that charges Supercapacitors quickly from a standard wall socket (120v) then releases the electricity back out at 5 volts 1 amp.

Can someone help me figure out what it would take to achieve this?

Thanks a ton!

-T

2. ### kubeek AAC Fanatic!

Sep 20, 2005
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the exact type of the capacitor?

3. ### tgauss Thread Starter New Member

Mar 11, 2013
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That is up for recommendation. I am looking for the smallest possible solution that is capable of handeling at least 1220mAh.

4. ### praondevou AAC Fanatic!

Jul 9, 2011
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Capacitors do not discharge as batteries do. The voltage drops rapidly when connecting a load.

http://www.digikey.ca/Web Export/Su...l-ultracapacitor-cell-sizing.pdf?redirected=1

http://cds.linear.com/docs/en/design-note/dn450f.pdf

http://www.overclockersclub.com/news/32206/

For how long do you want to supply current?
What are space requirements? (an supercapacitor with comparable energy storage capacity is much bigger than a battery)

You would need a circuit that maintains a constant output voltage with decreasing input voltage.

5. ### kubeek AAC Fanatic!

Sep 20, 2005
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that is hardly going to happen, at least in the way you probably imagine as "small". 1220mAh at 5V equals to 22kJ stored (assuming you can somehow extract it tall)

A supercapacitor bank say at your 120V will need to have a capacity of about 3F. I bet it would be about as large as a family car's lead acid battery.

Looking a little on the web, you would for example need 44 of these in series to make that bank http://www.dhgate.com/super-capacit...itors/p-ff80808130e5a5220130f6ebb9393976.html ok that would be about a half of a car battery based on those dimensions.

Or you could use some other voltage and get some different capacitance and find something a little more suitable, but still, the size will be significant.

6. ### tgauss Thread Starter New Member

Mar 11, 2013
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I am looking to recharge a 1420 mAh 4.7v battery.

7. ### tgauss Thread Starter New Member

Mar 11, 2013
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I could use a transformer so the input voltage is whatever is ideal.

8. ### kubeek AAC Fanatic!

Sep 20, 2005
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Seems to me like some kind of portable recharger, so do you plan to leave it chraged for long periods of time? Supercapacitors have high leakege current, so I guesstimate they would loose like a half of the charge after 24h.

9. ### tgauss Thread Starter New Member

Mar 11, 2013
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I would be a portable recharger. It would be used almost immediately after charging so the leakage would not be an issue most of the time. My goal is to rapidly charge the capacitors then be able to take it with me to charge the battery portably.

10. ### praondevou AAC Fanatic!

Jul 9, 2011
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Wouldn't it be easier to take the 4.7V battery to whereever you charge the capacitor and chare the battery instead? Or is that not possible?

11. ### tgauss Thread Starter New Member

Mar 11, 2013
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My hopes (tell me if I am wrong) is because I will have brief limited time to an outlet, that the Capacitors would be able to be filled more rapidly than a battery would. Then I can take the charged capacitors and have them fill the battery portably with me. Would/could that potentially be the case?

12. ### kubeek AAC Fanatic!

Sep 20, 2005
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Theoretically it should be possible, but you need to accept that it will cost a lot of money, and it won´t be very small, I would guess at least the size of a shoe box. Also it will take a lot of time to develop the necessary circuitry to charge the caps and deliver the charge to the load.

Mar 11, 2013
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14. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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4.7V @ 1120mAH = 18950400 Joules or
$\mathsf{\approx19x10^6 Joules
\approx 19 Mega Joules}$

$\mathsf{\frac{1}{2}C\cdot V^2}
\frac{1}{2}400\cdot 25
5,000 Joules$

Seems you'll need about 4,000 times more capacitance to get the same life as a 1120mAH battery, assuming you can use 100% of the capacitor charge, which you can't, so maybe 5000 times more capacitance, a 2 MegaFarad capacitor rated at 5V should do it.

15. ### pilko Senior Member

Dec 8, 2008
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@ thatoneguy

"4.7V @ 1120mAH = 18950400 Joules or
$image=http://forum.allaboutcircuits.com/mimetex.cgi?\mathsf{\approx19x10^6+Joules\approx+19+Mega+Joules}&hash=8df79f3e93bd83abc9a3d4c32bd3b0dc$"

They are mAH not AH. The energy would be approx 19 Kilo Joules.

16. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
725
DOH! I hate it when that happens!

19 KiloJoules (18.9504x10^3 J to be exact)

So, only 5 sets of caps would match the battery, but I think they wouldn't get much over on charge time compared to the fast charging Li-Ion, depends on their thermal properties/charge rate.

Feb 25, 2013
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18. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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Why don't u use two or three batteries instead

It would be cheaper