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



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