Re: Build own capacators

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: m.j.watts@xxxxxxxxxxxx 

On 19 Dec 2005, at 23:42, Tesla list wrote:

> Original poster: "James Zimmerschied" <zimtesla@xxxxxxx>
>
> Malcomb,
> I may pull the assembly apart and measure the individual caps (25
> total) for an "odd" one. I didn't notice any external arcing.
> Jim

If internal arcing is the problem, measuring is unlikely to find a
problem unless it is done at close to the capacitors' rated voltage.

_Malcolm_

> ----- Original Message -----
> From: <mailto:tesla@xxxxxxxxxx>Tesla list
> To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
> Sent: Monday, December 19, 2005 12:04 AM
> Subject: Re: Build own capacators
>
> Original poster: <mailto:m.j.watts@xxxxxxxxxxxx>m.j.watts@xxxxxxxxxxxx
>
> On 16 Dec 2005, at 22:31, Tesla list wrote:
>
>   > Original poster: "James Zimmerschied"
> <<mailto:zimtesla@xxxxxxx>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
>
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