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=?iso-8859-1?Q?Re:_Ed=B4s_Amps_(was_cap_failure...)?=



Tesla List wrote:
> 
> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
> 
> Hello Ed, all
> 
> (I´m slowly, slowly catching up on my mails)
> 
> I wrote:
> 
> "the 3/8" doesn´t get warm at all, my tuning coil (which is only a
> fraction of the µHs of my primary coil) gets pretty warm during
> a run. After a 5 minute run it is very slightly uncomfortable to
> the touch (guessing 40-45°C).  I  am running a static gap, so I
> couldn´t tell you my BPS. I am guessing it is over 100 BPS (50Hz),
> but I wouldn´t bet on it."
> 
> Ed wrote:
> "My primary does get warm, but not uncomfortable to touch (my definition
> of hot).  The HV ceramic filter capacitors I am using get so hot that I
> can't run them more than a couple of minutes at a time without losing
> some."
> 
> Hmm, It would seem as if you are "wasting" energy in your
> ceramic caps. Are you using these in an RF filter or as your
> primary cap? If you are using them as a tank cap, you might
> actually have less current flowing in your primary circuit than a
> calculation might lead you to believe (~300A). I am using MKP
> (polyprop) caps and they don´t get wam at all. As a matter of
> fact, I can´t measure a temperature change at all (over a run
> period of 5-6 min).
> 
> Are these ceramic caps the thin disc type? I have heard they
> have pretty high internal losses and die quickly in TC usage.
> I believe Mike Hollingsworth has tried using these.
> 
> A while ago, I was using some of PCI´s caps. These were DC
> filter caps in a glass vessel. These got so hot (~30 sec run time
> on my 200W OBIT coil) that they cracked. The dielectric was
> (as far as the info on PCI´s homepage goes) Mylar, which
> certainly would explain the rotten spark output I got and the
> heating effects the caps were experiencing. I was probably
> putting more energy into the heating of the caps, than into the
> primary coil.
> 
> BTW: My tuning coil does NOT get hot, just more than slightly
> warm. It is a sort of "in between" temperature. However, I have
> to add that the "room" temperature is around 0°C (my coiling
> room isn´t heated), so in summer the tuning coil temp might turn
> into "hot". I hope to have gotten rid of the tuning coil by summer,
> tho. Another reason for the temp rise in my tuning coil might lie
> in the fact that it is made out of hard steel brake line (iron is
> a worse conductor than copper and it will experience magnetic
> field problems as well).
> 
> Coiler greets from germany,
> Reinhard

	The ceramic capacitors I am using are rather large HV filter
capacitors, marked as 0.004 ufd, 30 kV.  There were a bunch of them
available quite cheaply a year or so ago.  They do have low-inductance,
low-resistance connections (capacitor is a single disk about 1/2" thick
and 2-1/4 inches in diameter, with silver-plated connections to threaded
studs), and the losses are low enough that they perform to my
satisfaction if I keep the run times down.  I have better capacitors,
but these are small and convenient.

	As far as the little disk types are concerned, depending on the
formulation, they will have terrible temperature coefficient and
dielectric hysteresis loss.  I suspect that a bank of them connected in
series/parallel (series strings in parallel to help keep the effective
series resistance down) would be a whole lot better than nothing at
all.  Certainly better than the glass plate capacitors I used to make
when I didn't know any better.

	Without calculations I'm too lazy to perform, not sure whether the
losses in your steel hydraulic lines are affecting the performance of
the coil.  If the windings don't get very hot while you are running
hundreds of watts of power, would think the losses are tolerable.

Ed