Power Supply capacitor physical size

[John Robertson]

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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