capacitor question

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

  1. wes

    Thread Starter Active Member

    Aug 24, 2007
    242
    2
    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
    0
    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.

    More information can be found on the Internet with a google search.

    hgmjr
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    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 :)
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
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  6. wes

    Thread Starter Active Member

    Aug 24, 2007
    242
    2
    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.
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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  8. chesart1

    Senior Member

    Jan 23, 2006
    269
    1
    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
    0
    that's a good point chesart1, i never thought of it that way before
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    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
    2
    alright well thx, and yea I do have problem with run-on sentences, lol
     
  12. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    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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