capacitor question

Discussion in 'General Electronics Chat' started by wes, Mar 18, 2008.

1. wes Thread Starter Active Member

Aug 24, 2007
242
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hey would it be possible to hook up say 50 2.5 volt at 1.5 F capacitor's in series to up the voltage and then hook up 50 in parallel to up the Farads so you would have (i may be wrong but from what i read) 125V at 75 Farads and then use it to pulse something like a rail gun or coil gun and a very fast rate so the power would be like way higher but only for like 1/2 a second, if you could'nt then could you please tell me why and anyone know's where i could go to read up more on them and especially the equations on capacitors

2. John Luciani Active Member

Apr 3, 2007
477
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That is unlikely to work.

Most supercaps have a fairly high ESR (effective series resistance). If you start
drawing large surge currents you will generate a lot of heat and destroy the
capacitors.

(* jcl *)

3. hgmjr Moderator

Jan 28, 2005
9,030
214
Take a look at the material at this link to the AAC ebook section on capacitors.

hgmjr

4. SgtWookie Expert

Jul 17, 2007
22,183
1,728
Capacitors connected in series are calculated like resistors in parallel.
1 / Ctotal = 1 / C1 + 1 / C2 + ... 1 / Cn
- or -
Ctotal = 1 / (1 / C1 + 1 / C2 + ... 1 / Cn)
So, by the time you connected 50 of those 1.5 F caps in series, you'd have a net value of 0.03 F.
In order to get 75 F from series strings like that, you'd need 2,500 strings - a total of 125,000 caps.
I hope you have a very large workbench

Jun 30, 2006
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6. wes Thread Starter Active Member

Aug 24, 2007
242
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hey thx for all the input and i was wondering what happens if you put like a 9V and a 1.5V in parallel, would the voltage stay 9 volts or would it be 1.5 or somwhere in between like 5v and if it was 9 or 1.5 wouldthe 9 volt be trying to charge the 1.5.

May 16, 2005
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8. chesart1 Senior Member

Jan 23, 2006
269
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Capacitors in series in a DC circuit is not a good practice because you cannot be sure that any one capacitor won't assume too large a charge. The typical method is to have a resistor in parallel with each capacitor to ensure that each capacitor is charged to the correct value.

9. rwmoekoe Active Member

Mar 1, 2007
172
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that's a good point chesart1, i never thought of it that way before

10. beenthere Retired Moderator

Apr 20, 2004
15,815
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The idea may not be impractical. I can't find the link, but there is an outfit that provides gear for wind turbines that uses ultracapacitor banks for power to feather the blades in stormy conditions.

I thought it was odd that they would have to use a booster to do the deed when generating conditions are pretty good, but that was what the copy said.

11. wes Thread Starter Active Member

Aug 24, 2007
242
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alright well thx, and yea I do have problem with run-on sentences, lol

12. nomurphy AAC Fanatic!

Aug 8, 2005
567
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Fifty 1.5F, 2.5V, caps in series would give you 0.03F at 125VDC. You would then need to parallel another 49 strings of 50 caps in series to get back to 1.5F (0.03F x 50) at 125VDC. That would be 50 x 50 = 2500 caps, not cheap!

Please see attached for cautions in using such caps.

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