Re: Flat Electrolytic Capacitors

On Mon, 12 May 2008 19:49:26 -0700, D from BC
<myrealaddress@xxxxxxxxx> wrote:

On Mon, 12 May 2008 07:31:46 -0400, legg <legg@xxxxxxxxxxxxxxx> wrote:

On Sun, 11 May 2008 20:08:50 -0700, D from BC
<myrealaddress@xxxxxxxxx> wrote:

I stumbled across this...
A 330uF 200V flatpack capacitor.
http://www.cde.com/catalogs/MLS.pdf
It's 1/2" thick.
And also costs over $100 ea (mouser)
Yikes!

I need flatter...

I'd like to know if I can get 150uF @200V crammed below 10mm without
resorting to paralleling many capacitors.
Can be axial, radial or SMD.
Any mounting orientation is ok..
Currently Googling and browsing Digikey...


UCC/NCC used to offer a high voltage FTK series that was radial lead
in an oval package - still 12.5mm minor dimension. Don't see these
advertized anywhere, now. 10mm can often be wangled to 12.5 by
removing printed wiring in the viscinity of the part body.

Flatness is often a bull*** requirement - research it carefully.

What's the actual requirement? Filtering? Energy storage? Hold-up
time? These can often be adressed more intelligently than by just
adding uF.

RL

I suppose it would be hold up time.
If the ripple current is too high my smps drops out of regulation.
150uF was the min. capacitance determined.
Also, and this is something I have to do homework on...
I believe the more ripple current, the shorter the capacitor lifetime.
My app has to run for about 7 years continuously.
IIRC the capacitor ripple current is about 0.5A peak-peak.

Nothing at that power level 'needs' to be 10mm thick. It's not hold-up
time if it happens on a cycle by cycle basis - hold-up is a one-shot
deal at power down.

That said, increasing the stored input voltage may reduce the part
body size for the same CV^2 /2 energy storage. That's one of the
features of pfc boost - it can also be a feature without regard for
pfc. Simple voltage doublers get the same effect. The idea is to never
let the storage energy get that low in the first place - it should
only occur for brown-out, ride-through or hold-up time conditions.

Extending regulation range (lower drop-out) gets more energy out of
the capacitor. At lower powers it's no big deal, so long as your 10mm
thick package has sufficient surface area to dissipate the losses.

Pyrotechnics to alleviate LF dropout effects can also be performed on
the secondary side, where real-estate is higher density, voltages are
lower and technology is your friend.

This 10mm thick package is likely custom - there are thieving methods
applicable to body wall thickness that can be used to scavenge extra
millimeters for internal parts. Open up a flat battery pack.

I think there's an unstated rule of thumb with commercial electronics
that the thinner something is, the quicker it gets busted, which sort
of works against the 7-year aim.

RL
.

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