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Re: Unexplained arcing current
to: Gary
You may be getting some resonance with your bypass caps if they are too
large. I usually use 3 --- 100 pF in series for around 33.3 pF total cap
off each bushing. I noticed that larger values can sometimes cause unwanted
resonances and heat up the resistors.
Regards,
Dr.Resonance
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, May 28, 1999 4:28 AM
Subject: Re: Unexplained arcing current
>Original Poster: Gary Lau 27-May-1999 0714 <lau-at-hdecad.ENET.dec-dot-com>
>
>There WAS a resistor between the bypass capacitor and the gap. The
>two 450pF bypass caps were each across the NST terminals and ground, and
>the two 1.6K/113W resistors were from the NST terminals to the main gap
>terminals.
>
>I believe this situation where the tank was disconnected resulted in MUCH
>hotter resistors than in normal operation. I think the explanation that
>I gave where the bypass cap energy is dissipated in the R's adequately
>explains the heating. The same thing occurs in normal operation, but
>since the BPS is so much lower, the additional power from this is not
>that significant. If I assume my main gap fires at 25KV 150 times per
>second, my bypass caps would only contribute about 10.5 Watts to the two
>resistors.
>
>
>Regards, Gary Lau
>Waltham, MA USA
>
>>Original Poster: "B**2" <bensonbd-at-erols-dot-com>
>>
>>Hi Gary, All,
>> What happens when you put a resistor between the bypass capacitor
>>and the gap?
>
>
>>>Original Poster: Gary Lau 25-May-1999 1022 <lau-at-hdecad.ENET.dec-dot-com>
>>>
>>>I believe I've figured out why my resistors get so hot. Well, almost.
>>>
>>>Recapping, with my tank circuit disconnected so that my 15KV/60mA NST
>>>just fires my 0.36" static gap through my RC protection network, the
>>>series resistors (1.6K/113W non-inductive film) get hot very quickly, but
>>>if I disconnect the 450pF bypass caps, they do not.
>>>
>>>I realized that with my tank cap no longer in place, the bypass caps will
>>>charge many, MANY times per mains half cycle. I quick simulation showed
>>>that if the static gap were set to 15KV, it would charge and discharge
>>>128 times per half-cycle. The RMS current through the resistors is over
>>>250mA! That will do it!
>>>
>>>Only problem is, I also have this hot resistor problem to a similar
>>>degree when my tank circuit is in place and the bypass caps may only
>>>charge the same number of times as my main cap does, a couple of times
>>>per half-cycle at most. Still looking...
>
>