Power Supply capacitor physical size

Jon Elson elson at pico-systems.com
Sat Sep 3 10:19:58 CDT 2016

On 09/03/2016 08:02 AM, Adrian Graham wrote:
> Hi folks,
> Looking at the PSU of my Lisa's ProFile after it died gracefully not so long
> back and it obviously needs new caps since one of the 1000uF 16V ones has
> bulged badly. While I'm replacing that one I'll do the 47uF 250V ones too.
> And the mains filters but I've got a stock of spares for them already.
> Apologies for what's probably a dumb question, but when it comes to cap
> replacement I know I can go up a notch if the required capacitance or
> voltage isn't available so 25V and 400V is ok, but what about physical size?
> I can get the correct capacitance/voltage but they're physically much
> smaller than the ones I'm replacing, like 10mm instead of 16mm diameter. If
> I go up to 25V I can get 16mm diameter which is the size of the old ones.
> Am I worrying for nothing?
Maybe not.  Capacitors that are subjected to high AC ripple 
current may need the large surface area for cooling.  
Possibly using a low-ESR capacitor will help reduce heating, 
but might have other undesirable effects.
So, you need to know a bit about the circuit and the 
stresses placed on the capacitors to decide.  if the ripple 
current is low, then smaller caps are no problem at all.


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