Re: Build own capacators

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: m.j.watts@xxxxxxxxxxxx 

On 16 Dec 2005, at 22:31, Tesla list wrote:

> Original poster: "James Zimmerschied" <zimtesla@xxxxxxx>
>
> Hello Terry and others on the List,
>
> Some discussions about home built oil capacitors and performance:
>
> I tried a little experiment with a small coil running a 30 ma NST. I
> tuned the coil to run on 0.009 microF CD 942 MMC and observed the
> streamers. Then I tried two 0.018 microF rolled poly oil caps in
> series (0.009 microF). I retuned slightly to get the best output. The
> streamers were very similar in length and color. Then I tried a
> series set of barium titanate ceramic caps which I borrowed. These
> were also 0.009 microF. The streamers were again about the same. As a
> final test I used a 0.009 microF MMC made up of mica caps (2500 VDC
> 0.01microF). These gave less spark length than the other types I
> tried (11" vs 16").
>
> I also put a small incandescent bulb's filament in series with the
> coil's secondary at the ground end to observe current draw in the
> secondary. In this test, the rolled poly and mica caps produced the
> most current (i.e. brightest glow in the bulb filament). Next was the
> barium titanate and last was the CD MMC. It is not clear to me why
> the CD MMC and the rolled poly produced similar arc quality when the
> bulb indicates the power to the streamers was higher with the rolled
> poly caps? Also puzzling is why the mica caps performance was low
> when the power in the secondary was at least as high as the rolled
> poly caps based on filament glow.
>
> The conclusion I reached was that any of these types of caps (except
> maybe the mica caps) would be good for this size of coil. The rolled
> poly caps certainly equaled the CD MMC in performance at the expense
> of being bulky and an oil spill hazard.

I wonder whether one of your mica caps was flashing over
internally, something that would change the operational
capacitance and hence tuning? The higher capacitance might also
account for the result you got with your secondary coil expt. In my
experience, Sangamo micas are of excellent quality with a price to
match. I was lucky enough to be given a cartonful of assorted
values once. The only TC I ever sold (a smallish "safe" one) used a
pair of 3n9 6kVW Sangamos in parallel as the primary cap. AFAIK
it is still going strong after 5 years.

Malcolm