RE: [TCML] Resistant Spark Gap

["Lau, Gary" <Gary.Lau@xxxxxx>]

Hi Brandon,

Brass balls are a good choice for the safety gaps in a Terry filter.  As you noted, the round shape (large radius of curvature) results in a higher and more consistent breakdown voltage, and that's a good thing.

Ball gaps are not a good choice for the main static gap however.  The problem is that for a gap that fires more than occasionally, the arc will always occur at the same place on each sphere, and this will result in both localized heating (which affects the breakdown voltage) and rapid erosion of the sphere.  One ideally wants the arcing surface to be as spread out as possible.  This is why cylinder gaps (two or more parallel copper pipes) are popular.

Regards, Gary Lau
MA, USA


> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Brandon Hendershot
> Sent: Saturday, December 19, 2009 12:23 PM
> To: Tesla Coil Mailing List
> Subject: [TCML] Resistant Spark Gap
> 
> I found a link someone put up on the list of site that sells brass
> balls for pretty cheap. I ordered a few for my spark gap and soon to
> come Terry Filter. The problem is, the gap needs to be half the size
> it was before in order to fire. Is it because the electrodes are now
> round and have less of a preferance of where to arc to? Or are they
> acting like a resistor on the high voltage?
> 
> Other things I've changed are the connecting wires and the screws
> since I needed bigger ones for the balls to screw on to. But I've
> checked the resistance with an ohmeter and they are the same... Any
> words on this?
> 
> Thanks a lot, guys.
> Brandon

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