Re: best capacitors for high ripple and large capacitance
- From: Tom Bruhns <k7itm@xxxxxxx>
- Date: Thu, 10 Apr 2008 13:35:37 -0700 (PDT)
On Apr 10, 5:52 am, Jamie Morken <jmor...@xxxxxxx> wrote:
Hi,
What is the best capacitor to use for this?
63V+ rated, 1250uF min capacitance, 15Arms 200kHz ripple rating
I was looking at electrolytic's, it would take 3 of these caps to get
15Arms ripple handling:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P749...
that would be 30000uF though! :)
Also that caps 5Arms ripple rating is at 10kHz, would this rating
increase or decrease for 200kHz typically for an electrolytic?
cheers,
Jamie
The way I'd normally think to handle something like this is to NOT use
an electrolytic directly, since they invariably have high enough ESR
that 15A RMS will cause significant heating. Rather I'd handle the
ripple with some very low ESR capacitance: ceramic or more likely
polypropylene in this particular case. WIMA make some very good
polyprops for applications like this. Use enough capacitance to get
the ripple voltage down to a reasonable value, and then you don't need
much inductance between that and bulk electrolytic capacitance to keep
the ripple current in the electrolytic at a more reasonable level.
Check out the WIMA MKP10 series. Panasonic ECWF and Vishay MKP379
series should also work well. Five 4.7uF 100V caps in parallel should
very easily handle the current and get the ripple down to a couple
volts p-p or less (depending on waveform). Even two or three would
handle the current easily, but might not get the ripple voltage low
enough--your design, your tradeoffs. Then even a fraction of a
microhenry off to bulk capacitance limits the ripple in the bulk to a
low value.
Cheers,
Tom
.
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- From: Jamie Morken
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