Power Supply capacitor physical size - test-drb@ccmp.vtda.org

3 Sep 2016

On 09/03/2016 10:07 AM, Adrian Graham wrote:
...
  On 03/09/2016 17:39, "Jon Elson" <elson
at pico-systems.com> wrote:

  On 09/03/2016 10:56 AM, Noel Chiappa wrote:
   From: Jon
Elson
> needs new caps since one of the 1000uF 16V ones has bulged badly.
> ...
> If I go up to 25V I can get 16mm diameter which is the size of the old
> ones.
 Capacitors that are subjected to high AC ripple current may need the
 large surface area for cooling.  Interesting point - but in his particular case, he
should be OK replacing the
 old 16V cap with a similar-sized modern 25V cap?

  Similar size - then no problem!  But, some new cap types are
 VASTLY smaller than the caps from 40 years ago.  Hence my question, I'll stick
with the same size but higher voltage.

 Cheers!

You do have to consider where in the circuit the capacitor is. If this 
is a switching power supply (as I suspect) then if the cap is after the 
switching transformer it MUST be a low ESR, high temp cap - otherwise it 
won't last very long. If this is on the primary side and is simply 
filtering the input rectified AC then ESR is not as big a problem, but 
you need a good physical size if the switching supply puts out a fair 
bit of current due to heating effects of low frequency ripple.

So, it all depends.

For general repair I would get the best grade of capacitor - say 
Panasonic - with a nice low ESR and away you go.

John :-#)#

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