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Increasing Capacitance...
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Tuesday, September 23, 1997 7:53 AM
To: Tesla List
Subject: Re: Increasing Capacitance...
>
> From: David Huffman[SMTP:huffman-at-FNAL.GOV]
> Sent: Monday, September 22, 1997 10:35 AM
> To: 'Tesla List'
> Subject: RE: Increasing Capacitance...
>
I have sent pictures of two situations involving the use of
different oils of different dielectric constants. If the space
between the foil and the film is occupied by oil of a similar
dielectric constant as that of the film then the voltage stress on
the film will be lower than if the oil has a higher dielectric
constant. It might be wise to avoid large differences in this
constant as was pointed out in previous messages. Like all aspects of
coiling there is a trade off. The gain in capacitance will be had by
the loss in voltage rating. Imperfection in the film might be
magnified by the higher dielectric constant oils.
> Thinking out loud, zap me if I need it.
> Dave Huffman
>
>
Dave,
No need for any zapping today :)
We need to look at all the factors involved in using oil with a
higher dielectric constant. Each factor needs to be evaluated
carefully and the good and bad points carefully weighed. It seems
like everything is a trade-off. But how much of a trade-off? How good
are the good points, how bad (in actual practice) are the bad points?
We need thoughtful discussion, but even more than that, we need cold
hard facts. There is nothing like actual experimentation to verify
the validity of our ideas.
Your remark about the different dielectric constants causing an
uneven voltage stress is absolutely correct. BUT I am not advocating
using thinner poly sheets or anything like that.
Here's the direction my thoughts are taking me: Take an existing HV
cap design that has adequate poly insulation, but instead of using an
oil with a dielectric constant of say, 2, use an oil with a
dielectric constant of say, 4. EVEN THOUGH the oil layer between the
plate and poly is very very thin, it has the effect of increasing the
capacitance significantly. As in Double the capacitance. That sounds
like good news to *me*! Assuming again that the poly is adequately
thick to act as the primary insulation, it seems that the trade-off
here is minimal.
The reports that I have read from those who have used the higher
dielectric constant oils seem to indicate that the increased
dielectric constant oil works just fine. No one reported a greater
tendency for these caps to break down or any such thing. Remember
that the oil thickness is small compared to the poly thickness. The
poly takes the lion's share of the voltage stress. So design it such
that it is capable of taking the entire stress. Which is what most of
us do anyhow.
To make sure there is always some oil between the plate and the poly
it might be very useful to use the method of putting paper beween the
plate and poly.
Because the oil layer will generally be much thinner than the poly
thickness, I don't think that there is anything to worry about in
this form of construction. The key is to ensure that the poly ALONE
is capable of taking the FULL voltage stress. If this is done, then
the fact that the stress is *more* across the poly than across the
oil will not have any appreciable negative results.
The reason why I have asked those who have used the higher dielectric
constant oils to e-mail in their experiences is so that we can gather
the input necessary to evaluate whether this is in fact a good way to
go. Everything I have seen so far says that it IS. So now the
question is one of trying to identify what oils with high dielectric
constants are available, and which ones are good for us to use.
Alfred Srocki has mentioned that SUNISON oil was OK, but Pyrin oil
was dangerous to the eyes. I have appended Alfred's post for those
who might find this topic of interest.
The really nice thing about using this method to increase capacitance
is that it is so easy to implement. All you have to do is use a
different type of oil.
Hope this helps.
Fr. Tom McGahee
********
From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent: Friday, September 19, 1997 1:59 PM
To: Tesla List
Subject: Re: Increasing Capacitance...
On Friday, September 19, 1997 2:43 PM Thomas McGahee
[SMTP:tom_mcgahee-at-sigmais-dot-com] wrote;
> ...Alfred Skrocki mentioned that he also used Sunison oil
successfully.
> But he didn't mention whether he noted the increase in capacity
over
> using regular mineral oil or transformer oil.
Sorry about that! Yes, the Sunison oil yielded about double the
capacitance of the same capacitor using mineral oil! I had even
better results once when I tried Pyrin oil, but that stuff is really
nasty! I accidently got a little on my hands and forgot and rubbed my
eyes, GOD did it burn - I thought I was going to go blind. The
emergency room informed me that Pyrin oil was notorious for causing
permanent eye damage so I don't play with it any more.
Sincerely
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Alfred A. Skrocki
Alfred.Skrocki-at-CyberNetworking-dot-com
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