Re: Safety gap taking over

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

At 08:34 AM 2/23/2004, you wrote:
>Hi everyone!  Last night I had my first light after my first failure.
>During the failure, my homemade parallel plate cap internally arced over
>so I decided to go the Geek group MMC route.

That happens a lot ;-))

>I will give a quick
>rundown of my specs:
>
>PS: 4 - 15 kV 30 mA NST's wired in parallel
>Cp: 32 nF Geek group MMC
>Terry filter with safety gap set to just NOT fire (safety gap is just 3
>brass balls about .5" in diameter)
>8 segment static spark gap using 1" copper pipe couplers set to just
>fire
>Secondary:  980 turns of #23 on a 4.25" diameter PVC form (which I think
>is too small given my input power)
>Topload: 4.25" x 23" toroid made from black drain pipe covered in Al
>foil tape
>
>Here is my problem:
>While running the coil, as I turn up the input power the spark gap
>begins to fire and as I turn up the voltage more, the safety gap does
>the job of the spark gap.  Keep in mind that I set the spark gap to just
>fire and the safety gap to just NOT fire.  When I set the spark gap to
>just fire, the safety gap was hooked up as well.  Does that change the
>breakdown properties of the spark gap?  I would think that it wouldn't,
>but I am not sure.  I even bridged a few of the gaps in the spark gap to
>reduce the firing voltage but the safety gap sometimes will take over.

I would say the main gap needs to be set a little closer.  Multitube gaps 
tend to increase their firing voltage with a little use.  I think that 
black stuff that builds up on them tends to increase the firing voltage 
since if you sand them down the voltage returns to normal.  You could also 
try increasing the safety gap setting just a tiny bit.


>I also have my Terry filter safety gap mounted upside down on the
>underside of the primary shelf.  I don't know if this would affect
>anything or not, but with no load at all, the safety gap acts like a
>Jacobs ladder.  Also interesting to note is that when the safety gap
>takes over the output still seems really decent...about 4' streamers
>once the surrounding air is sufficiently hot.  I also use a leaf blower
>to quench the spark gap that seemed to make the safety gap take over
>even faster.  Is there too much air flow here?  Sorry for the long post,
>but this has me a little confused.  Is the safety gap subject to a sort
>of avalanche effect where it fires ones, gets hot then keeps getting
>hotter and firing more often until it takes over?  Thanks to all in
>advance for your help!  I know it has been stated a lot, but without
>this list, there would be significantly fewer successful amateur coilers
>out there!

The safety gap might fire once in awhile but yours is firing too much.  Try 
the above and that should fix it.  If the safety gap gets hot, the ball 
type gaps like that may decrease in firing voltage.

Cheers,

         Terry


>Jeremy Gassmann
>Cincinnati, Oh
>http://jeremyee.tripod-dot-com