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RE: [TCML] Rotary spark gap plus NST? Good? Bad?

Using a sync RSG is the hands-down winner for squeezing the last inch out of an NST.  It's all about using the biggest "bang" size, and this is where sync RSG's shine.

It is often suggested that using async RSG's with NST's is bad for them, that the high break rates is somehow more stressful.  I think this is wrong, as the NST doesn't see or care how frequently the cap discharges.  I think the thing that gave asyc RSG's with NST's a bad rap was running the speed control too SLOW.  If the break rate goes much below 60 BPS, that allows mains resonant rise to ring the cap up to perilous voltages, since the gap isn't discharging it frequently enough.  Having a speed control knob on the RSG is the problem; the low end (or off) is dangerous.

Having a properly set safety gap in parallel with any RSG type is mandatory, to give a relief mechanism should the main gap fail, motor stall or go too slow, or whatever.  

Remember too that when using a sync RSG, a higher capacitance than when using a static gap will be required.  One can't get a bigger bang size if the cap size isn't any bigger.  Using a sync RSG with too small a cap may subject the cap & NST to too-high charging voltages.

My sync RSG is documented here:  http://www.laushaus.com/tesla/sync_gap.htm

I'm a big advocate of Terry filters (my thoughts detailed here: http://www.laushaus.com/tesla/protection.htm) but there are 3 independent protection mechanisms used there - the R-C low pass filter, the safety gap, and the MOV limiters.  The MOV's are probably the most pricey and you could just omit them to save some cost.  But the safety gap is essentially free and using that (and setting it properly!) is mandatory.

Regards, Gary Lau

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of mike osipowicz
> Sent: Monday, September 07, 2009 11:43 AM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] Rotary spark gap plus NST? Good? Bad?
> hello, I have a nice tesla coil, 12kv, 30 ma NST, with a boring old static gap,
> however the coil does put out 29 inch streamers. anyway, I am looking to upgrade
> to a rotary gap, I have a 1 HP, 1700 rpm motor, asynchronous... I'm not sure if it is
> o.k to use with my NST, I am worried about burning up my secondary windings. my
> caps are cornell dubliner brand, if I spelled that correctly... and the bank is at 12nf
> total. so, if I put 8 rotating, and two stationary electrodes, for approx. 170 bps, my
> nst has lasted a few weeks so far, but would would my nst last with a rotary gap,
> and my safety gap? I figured you guys were the ones to come to with this issue,
> p.s, I'm really not looking to spend the money/ time for a terry filter unless it is
> absolutely necessary, thanks,
> Mike Osipowicz

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