[Amps] Re: PS Theory (cap int res)

[Ian White, G3SEK]

kenw2dtc wrote:
>I have a bank of these computer grade caps in series:  2400 mfd at 450 vdc,
>2.5 inches in diameter and 4 inches long.  It looks like the PSU Designer
>program shows noticeable ripple if the internal resistance of the filter cap
>is too high.  How do I determine the internal resistance of my computer
>grade caps?  Is there a formula, or can they be measured with regular shack
>tools, or is there a ball park figure for computer grade caps, or perhaps an
>old wives' tale.

The quickest option is the manufacturer's website. Alternatively, try a 
good L-C-R bridge.

However, don't be worried about a small amount of ripple. With a  string 
of 6 or 8 capacitors, you must have 300-400uF in total, which is about 
10 times what most amps use. With so much capacitance, the ripple is 
probably only causing a few percent AM modulation at 100Hz. Other 
people's amps have 10 times as much 100Hz modulation and it's not a 
serious problem.

If you're going to worry, worry about the amount of energy stored in the 
capacitors (again, about 10 times as much as most amps have), and what 
might happens if so much stored energy lets fly in an HV arc.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek