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Replacing multiple caps... Don't have matching values...

Discussion in 'Beginner Electronics' started by Noozer, Jul 11, 2004.

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  1. Noozer

    Noozer Guest

    Howdy!

    I have a board with some failed capacitors. These are 3300uf 6.3v
    capacitors. I don't have any 3300uf caps handy, but I do have some other
    values and was wondering if a different combination of values could be
    substituted. The caps are connected in parallel (all + leads together and
    all - leads together) to filter a power bus.

    How can I calculate the resulting capacitance of these three parts combined
    and then break it into other values. (similar to how you could put two 500K
    resistors in series to substitute for a 1000K resistor).

    Thanks!
     
  2. Noozer

    Noozer Guest

    I have a board with some failed capacitors. These are 3300uf 6.3v
    DOH.. there are three of these capacitors in parallel.
     
  3. alpha_uma

    alpha_uma Guest

    This is a late reply, but FWIW.

    Cap values are added together if the caps are wired in parallel (in contrast
    to resistor values). So, to get close to 3300uF, THEORETICALLY you could
    wire two 1000uF caps and one 1500uF cap all in parallel (assuming you have
    caps of these other values handy). I think it would be much less of a hassle
    to order some 3300uF caps of the right sizes online from DigiKey or Mouser
    than try to pack three caps together in the space of one. This would be
    quite messy if the original 3300uF caps were already sitting side-by-side to
    each other.

    Make sure you order the ones with the correct diameter, lead spacing and
    maximum rated voltages. It is OK (better, in fact) to order ones with higher
    max rated voltages, but "higher rated V" means more money. I'd prefer ones
    rated at least 10V, but I could not locate any online store selling 3300uF
    electrolytic caps rated higher than 6.3V. For motherboard applications, I
    also wouldn't want to use any caps having a max temp rating of less than
    105degC. Just watch out that you don't accidentally order ones rated at only
    85degC (Ebay has lots of these).

    I recently ordered some 3300uF electrolytics (plus some other stuffs to make
    up a minimum order of thirty-some C$) from DigiKey, and they were able to
    ship them to me (for only 8C$) in less than 1.5 days. [BTW, if you happen to
    be in Canada, DigiKey can ship to Canada via Purolator which does not charge
    any "hidden" customs brokerage fees or customs handling fees.]

    Al-U
     
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