mike kendall wrote:
>Hello,
>
> Just wanted to do a QA on some capacitors that I've been buying on Ebay.
> They are Cornell Dublier 400wvdc 560ufarad caps. Intention is to put them in
> series for 4kv at 56 ufarads. These caps are so tiny that it makes me wonder
> if there is a power handling capability per cap that I should be concerned
> with or if they should be fine. Other concern is how many years can these be
> useful compared to a standard oil filled cap?
>
>
Looking at the Dubilier 560uF/400V cap that Mouser sells, size 35mm dia,
35mm high:
Ripple current rating is 2.7A. In a typical capacitor input supply,
that's equivalent to around 1.5A dc into the load.
If you keep the air temperature around them to 55C (130F) then they have
a life of 20,000 hours - that's 2.3 years continuous at 400V and 2.7A
ripple. Run them at lower temperature, lower ripple, lower voltage and
lifetime goes up significantly. Allow for the actual time they have
voltage across them, and ripple current through them, and they will
probably last your lifetime.
If you look up the actual parts you have, and measure the winding
resistances on your transformer, it's easy to firm up the numbers if you
want to contact me off list.
Steve
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