[Amps] CD Cap

[Ian White GM3SEK]

Rich wrote:
>Thank you Ian for your reply, please note that some of us are not real 
>sharp on all of this so I must ask how do I find the "ripple current 
>rating"? I bought the caps on ebay and did not find the info on CD's 
>web site.

Ripple current rating is the amount of alternating current that the 
capacitors can pass without too much internal heating. In a capacitor 
input supply, the caps are only charged in the parts of the cycle when 
the transformer voltage is higher than the DC voltage stored on the cap 
- and then a lot of current flows in a relatively short pulse. This 
results in a strongly "peaky" waveform of ripple current passing through 
the capacitor. (Can anyone point Rich to a graphic of the waveform on 
the web?)

In the kinds of power supplies we build for amps, the typical values of 
RMS ripple current run at 1.5-2x the DC current.

The effects of ripple current on capacitor operating temperature and 
lifetime are often underestimated, which is why I suggested you try to 
find out the ripple current rating.

Can you find these capacitors on the CD website at all? If the data is 
there, I would be surprised in the ripple current rating was not 
included.

Have you told us everything that is printed on the capacitors 
themselves?

>This also brings up another question, I am going to use an old 
>transformer. It has 230 input , three input terminals , out put is 
>terminals 1-2 , 3000vac , terminals 1-3 ,2090vac. Resistance is .45ohms 
>in(1-2) or 1.02ohmsin, output R is 41.4. In another thread it was 
>brought up about transformers for a choke input?? How do I tell and why 
>do I care. This is an old surplus transformer even to the point of 
>having spark gap balls in parallel with the output terminals.
>
This looks like one for the PSU Designer software.

(Sorry, it's well past midnight here, and there's a long day's driving 
to come tomorrow. Handing you over to the night shift, Rich... )


-- 
73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek