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Re: Many dry caps in series?
Hi Gary,
On Sat, 17 Oct 1998, Tesla List wrote:
> Original Poster: Gary Lau 17-Oct-1998 1702 <lau-at-hdecad.ENET.dec-dot-com>
>
> I'm considering a new capacitor design that uses 20 rolled poly
> capacitors in series, each using a single 6 mil LDPE dielectric. I would
> again use extended-foil construction with household aluminum foil. Would
> such a construction reduce the voltage per cap enough that it wouldn't
> create corona and be necessary to displace the air with oil? I'd love to
> avoid that whole oil-thing!
Hmmm, I've found LDPE to have a rough puncture voltage rating of around
420v/mil -at- 100KHz (2KVA). For an example scenario, say, 20 caps each with
a single dielectric layer of 6mil LDPE, means each cap (ideally) rated to
2520 volts -at- 100KHz. 20 in series thus yeilding a cap rating up to 50KV.
However, the main reason for using oil is for corona suppression - I've
found that corona tends to propogate much easier at a high frequency, a
lower voltage than normal, and higher energy levels. I've found that LDPE
goes under more stress (exponentially) as the power level goes up linearly
- especially when the frequency is rather high (> 70KHz).
Suggestions for open-air construction - make the edge-spacing for the foil
plates much larger, anywhere from atleast 1.5". ie, ensure that there is
atleast 1.5" outlay of LDPE around the edge of the plate.
Results from various experiments I've performed with LDPE caps has found
that in air, corona has always propogated, but not necessarily caused a
problem, ie breakdown, other than energy losses.
However, Give it a go! :-)
Let us know of your results...
Then, if you like, try under oil and note (if they occur) any differences
in both performance of the caps and the coil.
Cheers,
Rod
Tesla Technology Australia
http://www.tesla-technology-dot-com.au