Re: [TCML] Are safety gaps necessary?

[Quarkster <quarkster@xxxxxxx>]

ja -
   
  OOPS .... I omitted one critical detail. My Terry filter does NOT include any MOVs; only resistors, bypass caps, and the 3-ball safety gaps. When I first assembled the filter I was switching it between different coils with different NST voltages, and I did not want to keep changing the number of MOVs "in-circuit". I also felt that the MOVs were redundant, assuming correct adjustment of the safety gaps. 
   
   
  Regards, Herr Zapp
   
  jaholmes@xxxxxxxxxxxxxxxxxx wrote:
  Actually, Terry's original RC filter experiment had no gaps at all, nor any MOVs. It was just a couple of big resistors and a doorknob capacitor. A safety gap wouldn't have made much sense, since the intent was simply to measure attenuation of spikes and RF. I'd refer to the document on hot-streamer if I could, however as somebody pointed out in another thread, hot-streamer appears to be down right now :-(

I'd be a bit dubious of the value of *two* three-terminal gaps in a Terry-style filter. It seems like the point of the MOVs was to cancel out some of the human and environmental factors from the gap setting. If you don't use the MOVs, you're probably just as safe without anything on the transformer side of the filter capacitor(s).

--- On Thu, 6/19/08, Quarkster wrote:

> From: Quarkster 
> Subject: Re: [TCML] Are safety gaps necessary?
> To: "Tesla Coil Mailing List" 
> Date: Thursday, June 19, 2008, 3:12 PM
> Aaron -
> 
> One other observation on safety gaps. On a 6" X
> 30", NST-powered static gap coil of mine, I have a
> Terry filter with 3-ball safety gaps at BOTH the input and
> output of the filter. The 1K ohm resistors are 200W
> wire-wound units. The center electrode of both safety gaps
> is connected to the system's RF ground, which is a
> 3' length of 3/4" diameter copper pipe pushed into
> moderately damp soil within 5' of the coil. The NSTs are
> connected to the tank circuit with leads approximately
> 24" long. I measured the inductance of the wire-wound
> resistors at one time, but I don't recall the value
> right now.
> 
> I believe Terry Fritz' first experiments with his R-C
> filter network used 3-ball safety gaps at both ends, and I
> just copied his initial design.
> 
> Both sets of safety gaps are adjusted so they are just
> beyond the point of flashover at 140 VAC input to the
> paralleled 15/60 NSTs. During coil operation, depending on
> power level, primary tap tuning, number of static gap
> segments in use (total main gap width), and whether the
> coil is making air streamers or the streamers are attached
> to a grounded object, sometimes the safety gaps at the
> output side of the Terry filter will flashover, and
> sometimes the gaps at the input side will flashover. I
> don't recall ever seeing them flashing over
> simultaneously.
> 
> I have no explanation of why the gaps at the input side
> of the filter should ever be firing while the gaps at the
> output side aren't. However, it would appear that the
> gaps at the input side of the filter definitely saw (and
> shunted to ground) transients that otherwise would have
> gone directly into the NST secondaries.
> 
> Any comments are welcomed.
> 
> Regards,
> Herr Zapp

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