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Re: Test Cap, dry/oil
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Sunday, November 30, 1997 8:36 AM
To: Tesla List
Cc: gweaver-at-earthlink-dot-net
Subject: Re: Test Cap, dry/oil
Gary,
I read all the replies posted about this so far, and I have
this to add to the discussion:
If you measure the capacitance of the cap under oil you will
find that it is significantly higher. The oil has a dielectric
constant about double that of air, and in a homemade dry
capacitor you unfortunately have a lot of air interface
at the plates. This is true both for flat caps, rolled caps, and
believe it or not, even foil covered bottle caps. (Immersion
of bottle caps in salt water to act as the outer plate gives
a dramatic improvement in capacitance value and corona
reduction).
The addition of oil in your experiment is doing two things.
The air is getting expelled and replaced by oil. The
expulsion of air gets rid of much of the nasty corona problem.
This is where much of the heat was coming from. This corona
robs the cap of useful energy and also causes the poly to break
down chemically. Every time you use such a dry cap, it will
deteriorate further.
The oil gets rid of much of the corona and replaces the air that
has a dielectric constant of 1 with oil that has a dielectric
constant of about 2 or more. So your improvement is due to both
factors.
A slight additional improvement can be made by replacing the
smallish #24 wire with something having a larger surface area.
You are limiting the surge capacity of the cap by using such
a small conductor. All wiring that is part of the primary tank
circuit should be maximized for surface area if you want to get
the most bang for your buck. Remember that the highest resistance
part of the tank circuit will limit the performance of the rest
of the tank circuit. Everything in the Gap/Cap/Primary circuit
should be carefully chosen and connected such that large surge
currents can flow when the gap fires. The inductance of the
primary coil will then be the limiting factor. Even in a
miniature coil you want to be aware of these factors and design
accordingly. I suggest at least #18 for a truly miniature coil,
and at least #12 for a smallish desktop coil. Maximize surface
area.
Hope this helps.
Fr. Tom McGahee
>
> From: gweaver[SMTP:gweaver-at-earthlink-dot-net]
> Sent: Thursday, November 27, 1997 10:16 PM
> To: Tesla List
> Subject: Test Cap, dry/oil
>
> I made a test capacitor. Metal plates are 5" x 12" aluminum foil. 6 layers
> of 6" x 13" poly .006 mil. I put a #24 copper wire on each metal plate and
> rolled up the cap. Wrapped it with 2 turns of masking tape to hold it
together.
> The finished cap measures about 1.125" dia x 6" long. It measures .00129
> uf. on my meter.
>
> I connected the dry cap to a 6K 20 ma furnace ignition transformer and a
> tiny TC. The output sparks are 3" but not very hot. After 2 minutes of run
> time the cap started getting warm. I placed the cap in a small container
> and poured oil over it. The TC sparks are still 3" long but the discharge
> sparks are now much hotter.
>
> I have been thinking about making a dry poly rolled cap for a small portable
> desk top TC and did this test to see the results of a dry cap on the TC.
> The oil makes a big inprovement in the discharge sparks. The discharge
> sparks did not get any longer but the power output appears to be about
> double. Much thicker and hotter sparks.
>
> Gary Weaver
>
>
>