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
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