Electrolytic Capacitor Size

Discussion in 'General Electronics Chat' started by americanspirits, Jan 2, 2016.

  1. americanspirits

    Thread Starter New Member

    Jan 2, 2016
    I have a broken firewall that went out at work the other day. I decided to bring it home and open it up to find the problem. Looks like the capacitors on the power supply decided to bust open and there is a big burn mark on the top of the case from it. I ordered new capacitors from Amazon, same uf and voltage but when they got here they are different physical sizes from the ones currently on the power supply. My question is, which I think I already know the answer to, does the physical size make a difference in the capacitor if the specs on them are the same?

    Thanks in advance for your help and sorry for the dumb question - I am still searching on Amazon for the right CAPs to replace them with
  2. crutschow


    Mar 14, 2008
    Generally no, the physical size of an electrolytic capacitor is not a factor as long as the capacitance and voltage ratings are the same.
    A possible exception is, if it's a switching power supply that uses low ESR capacitors, then the sizes might be different.
  3. SLK001

    Active Member

    Nov 29, 2011
    Provided that the capacitors actually meet the specs, then no. Usually, only the diameter of the cap is the important measurement for fitting it on a circuit board (for devices not height constrained). Measure the diameter and select the value needed that meets the spec. Smaller parts with the same specs will have slightly different construction material - thinner foil, different electrolite, etc.

    For something that I wanted to work for a long time, I would replace with parts from an authorized dealer - like Mouser, Digi-Key, Newark, Allied, etc. It WILL cost more initially, but in the long run is actually cheaper.
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
    The fact that it blew it's top may mean it was working to hard or at to high of temperature. There are various flavors of capacitors - regular - usually rated at 85C, low ESR which run cooler, and 105C rated low ESR. There are probably more. Since you had a bad one I think I would google the part number or check a distributor like Mouser and replace it with one as good or better.
  5. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    Next time try to buy from know online electronics companies like Mouser ,Digikey and there are alot of other companies too.. This you get the best quality parts and find the exact part for the application ...
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    If you reduce the number of variables in attempting an apples-to-apples comparison, such as looking at one capacitor value/voltage across all of the Panasonic favors at Digi-Key, there is a general trend: cheap = small.

    As the operating temperature range increases, so does size.
    As the MTBF (Mean Time Between Failures, a measure of long-term reliability) increases, so does size.
    As ripple current capability increases, so does size.
    As ESR (Equivalent Series Resistance) decreases, size increases.
    As leakage current decreases, size increases.

  7. DerStrom8

    Well-Known Member

    Feb 20, 2011
    Never buy from Amazon or Ebay. That opens you up to the risk of buying fake components that will die quickly, if they work at all.

    As the others have said, buy from a trusted distributor like Digikey, Mouser, Avago, etc. Also, as a general rule when replacing electrolytic capacitors, find a replacement with the same capacitance and a voltage rating that is the same or greater than that of the damaged part. Furthermore, replace it with a 105C+ cap (preferred every time) and even better, a low-ESR type that explicitly states low-ESR. This will ensure the replacement will last a long time.

    Physical size only becomes an issue if, for example, the replacement is too big and forces you to mount it further up on the board, which potentially exposes pins, causes collisions with other components, brings it closer to heat sinks or other warm parts, etc. Electrolytic capacitors don't like getting warm--The electrolyte will dry up, causing the ESR to increase which leads to internal heating and eventually it will explode.

    If the replacement capacitor meets the rating requirements and does not cause any of the problems listed, it should be safe to use in your application.