Re: Glass/poly and more...
Sent: Sunday, September 14, 1997 10:42 PM
To: Tesla List
Subject: Re: Glass/poly and more...
A while back , perhaps 5 moths ago, I made a saline cap from
a very tall cylindrical wine bottle (Rene' Junot). The ouside was
wraped in aluminum foil, water sofner salt was poured in to the
shoulder level, then water water added to cover, motor oil filled
the remaining space as a sealant.
A small hole was drilled in the cork, and a #12 bare copper wire
was forced through it . The wire was then worked down the length
of the bottle as the electrode.
I then let it "settle" and it seemed that the air bubbled up into the oil
and out by itself! (cork was not fully installed).
Next step was AC seasoning with about 5KV for a few hours at a time.
Shortly after it's construction and preping, it measured 680 pf.
I must mention that was never used in TC service, but sat on the basement
floor for those 5 months. Now it reads 1200 pf.
Guess using a wine bottle makes it get better with age. (I'm joking)
Maybe the copper reacting with the salt is making copper cloride which
lowers the internal resistance and thus the impedance seen by the bridge?
I know you were looking for oil cap experiences, but I thought I'd throw
little experience in the ring anyway.
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Re: Glass/poly and more...
> Date: Sunday, September 14, 1997 2:50 PM
> From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
> Sent: Sunday, September 14, 1997 10:18 AM
> To: Tesla List
> Subject: Re: Glass/poly and more...
> Richard, Greg, Dr. Resonance, and others,
> All the answers given to Richard Smit so far have been correct, each
> in its own way.
> Greg is right, the glass is really bad, and adding a layer of poly to
> glass won't help much because the glass is still going to dissipate
> excessive heat in a Tesla coil application. I also note that Greg
> Leyh's reply was meant to be taken with a chuckle, and I enjoyed the
> humor it contained.
> Dr. Resonance brought up a good point regarding the resulting
> non-uniformity of the electrostatic fields that could lead to corona
> and breakdown. He rightly pointed out that a group of
> series-connected capacitor sections is the way to go.
> My own initial reaction to Richard Smit's post was:
> * It ain't gonna do any real good, because the poly has a
> * LOWER dielectric constant that the glass. The dissipation
> * factor of the poly will be better than the glass, but since
> * the glass is still the bulk of the dielectric material,
> * there isn't much to be gained by using a poly/glass
> * combination, since this baby is still going to run really HOT!
> I was figuring, what the heck, I have some time free right now, so
> I'll e-mail back and tell Richard all the things wrong with his
> suggestion. But then I realized that doing that would not really
> accomplish very much. The real question at hand was not so much what
> did Richard get wrong, but what did Richard get right?
> Richard Smit's idea of using poly with glass turns out to be
> something of a real bummer. For several reasons. However, I would
> like to take this opportunity to point out that while his choice of
> materials was not the best, his BASIC IDEA is not really that bad.
> Other members of this list have discovered that when they use an oil
> with a high dielectric constant, it can RAISE the capacitance of
> their homemade capacitor SIGNIFICANTLY, even though it represents a
> SMALL part of the total dielectric material involved between the
> plates. Most of the time the oil we use has a dielectric constant
> between 2.0 and 2.2, and so it closely matches the dielectric
> constant of the poly that we use. Thus we often don't see how much of
> an effect the oil can actually have on our caps.
> Here is a segment from a post to the Tesla List that I made on OIL
> recently. Among other things, it contains info I gleaned from a post
> by Ralph Down:
> > Some coilers have used refrigeration oil and silicone oils.
> > Ralph Down used SUNISO refrigeration oil (bought from local >
> refrigeration repair shop for $30 for 4 litres.)
> > He was pleasantly surprised to
> > find that the high dielectric constant of this oil actually
> > DOUBLED the capacitance value of his homemade capacitor.
> Obviously such a capacitor would loose some of its "extra"
> capacitance if it were physically compressed and the oil was pushed
> out from between the plates and the poly. A way to prevent this from
> happening is to use oil-soaked paper between the plates and the poly.
> Personally, I also use oil-soaked paper between the poly/poly layers
> whenever I use multiple poly layers between plates. (This is for poly
> that is 20 mils thick or more).
> By the way, Castor Oil has a dielectric constant of 4.67, whereas
> transformer oil runs between 2.9 and 2.2. Has anyone here on the list
> used Castor Oil for building a Tesla capacitor? I don't know about
> YOU, but *I* am greatly interested in making use of such stuff if it
> means I can cut the total physical size of my HV caps in HALF!
> A question that *I* have, which I have not seen addressed on this
> list before is: what is the long-term reliability and stability of
> capacitors made using oil with high dielectric constants?
> Ralph Down, how is your SUNISO oil cap working out? Have you measured
> it recently to see if its capacitance value has remained the same?
> Some people who have done post-mortems on their dead homemade caps
> have reported that the oil is often greatly changed in appearance and
> smell. Are we talking about transformer oil here, or something like
> motor oil? Is the damage that we see to the oil the *result* of the
> capacitor's death, or is it perhaps a partial *cause*? Some people
> have dissected live, healthy capacitors. What have YOU guys found?
> It sometimes takes guts to ask a question on this list. (It takes
> guts to attempt to give an answer, too, because sometimes in the
> process of answering, we make a mistake or two). But what I like most
> about the members of this list is that when all is said and done,
> there is a tremendous generosity at work here, a wonderful
> willingness to share knowledge and enthusiasm. To ask questions. And
> to attempt at least to answer them. Thanks!
> Hope this helps.
> Fr. Tom McGahee
> > From: Greg Leyh[SMTP:lod-at-pacbell-dot-net]
> > Sent: Saturday, September 13, 1997 5:00 AM
> > To: Tesla List
> > Subject: Re: Glass cap with polyethylene
> > Richard Smit wrote:
> > > I was wondering! Glass is a bad dielectric for a Tesla Coil but
> what if you
> > > take a thin piece of polyethylene and place it between the foil
> and glass.
> > > Will it still be a bad cap or will it be better because of the
> > It would be a far better capacitor -- provided that you remove the
> glass, as well.
> > -GL
> From: DR.RESONANCE[SMTP:DR.RESONANCE-at-next-wave-dot-net]
> Sent: Saturday, September 13, 1997 10:21 AM
> To: Tesla List
> Subject: Re: Glass cap with polyethylene
> To: Rich
> Using two different dielectrics in a cap is very bad. The
> fields will not be uniform which could lead to local corona and hence
> breakdown. Suggest using single sheets of plastic and then series
> connecting each subsection.