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RE: [TCML] BPS Testing
When I was using a static gap, I ALWAYS ran with 140VAC. If the knob goes up to 11, why stop at 10?
Beyond that, I seem to have been blessed with a 15/60 that's endowed with super-NST powers. I think it may have been bit by a pig that was exposed to ionizing radiation... Although the shunts are unmodified, I have scoped the NST secondary current, and clocked it (with a digital scope) at over 200mA RMS (not peak, not .707* peak, not a typo). Although the short circuit secondary current is still in fact 60mA, when the input voltage is maxed out and when using LTR caps, ferroresonance is the only explanation for this behavior. I *LIKE* it! This must be why I'm able to use larger than typical cap values (.02uF w/ static, .04uF w/ SRSG).
The mains current, even with PFC caps, was close to 20 Amps.
When ferroresonance occurs, the NST charging current can far exceed the normal, faceplate rating. Even with the BPS testing that you have just performed, you noted that occasionally you see one bang following another in quick succession. The only way for that to occur (assuming that the gap breakdown voltage is reasonably consistent) is if suddenly, the NST is pumping out a lot more current.
If the cap is charging but fails to achieve the gap breakdown voltage Vgap before the charging reverses, that energy in the cap is not lost, but must go somewhere as the cap voltage "charges" towards zero, and then on to -Vgap. That unspent energy manifests itself as (.5 I**2 L) NST secondary current, and I'm guessing that any additional charging current must be on top of that, the sum saturating the current shunts. That's my theory. And unfortunately, such behavior is not consistent from NST to NST or bang to bang, and is impossible to predict or model.
Regards, Gary Lau
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Monday, March 10, 2008 10:02 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] BPS Testing
> Hi John,
> There's more to it than variac at full. Gary's system had to be either
> pulling almost double the amps or there is something else not
> identified. Gary has stated that ferro resonance could be the cause. I
> am not so sure about that. If the NST was saturating, or ungrounded,
> maybe. A TC is certainly loaded, so I doubt loading plays a part. I can
> understand that if there was ferro resonance that the arc could start
> early at the gap, but the energy available in the cap hasn't changed
> (and spark lengths would be poor if so). The cap is a current controlled
> device (ferro resonance or not). I just can't understand how ferro
> resonance would affect much in TC service (but maybe I just don't
> understand ferro resonance well enough). However, if resonant charging
> is occurring, then I can understand the higher bps.
> Take care,
> > Bart, Gary,
> > Maybe Gary's analysis assumed 140VAC input to the NST?
> > That should raise the BPS a lot.
> > John
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