RE: NST Shunt Removal (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 11 Jun 2007 20:43:06 -0400
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: NST Shunt Removal (fwd)

The usual way that NST's fail is that excessive voltage (probably caused
by setting static gaps too wide) causes weaknesses in the potting material
to break down and carbonize, shorting some portion of the NST secondary
winding.  Removing shunts won't do anything that might raise the voltage
to cause such a breakdown.  It WILL result in higher current, which will
in turn cause the NST to run hotter.  Normally Tesla coils are run with
short enough run-times that it won't get too terribly hot.  If one did run
a de-shunted NST until it becomes super-hot, perhaps that might cause
carbonization of primary insulation.  Not something I'd recommend.

Regards, Gary


> ---------- Forwarded message ----------
> Date: Mon, 11 Jun 2007 18:04:05 -0400
> From: otmaskin5@xxxxxxx
> To: tesla@xxxxxxxxxx
> Subject: Re: NST Shunt Removal (fwd)
> 
> This was brought up by another coiler in an earlier post, but I don't believe anyone
> answered it.  Does removing shunts make an NST more susceptible to failure, or
> is it a safe way to increase output?  Thanks for any advice, Dennis Hopkinton MA
> 
> 
> -----Original Message-----
> From: Tesla list <tesla@xxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Sent: Mon, 11 Jun 2007 9:24 am
> Subject: RE: NST Shunt Removal (fwd)
> 
> 
> 
> 
> --------- Forwarded message ----------
> ate: Sun, 10 Jun 2007 18:33:34 -0700
> rom: Jim Mora <jmora@xxxxxxxxxxx>
> o: 'Tesla list' <tesla@xxxxxxxxxx>
> ubject: RE: NST Shunt Removal (fwd)
> Hello,
> I too modified a France 12/30 removing half the shunts and potting it a
> ixture of melted Vaseline and paraffin. It arcs a Really hot flame!
> Jim Mora
> -----Original Message-----
> rom: Tesla list [mailto:tesla@xxxxxxxxxx]
> ent: Sunday, June 10, 2007 3:51 PM
> o: tesla@xxxxxxxxxx
> ubject: NST Shunt Removal (fwd)
> 
> --------- Forwarded message ----------
> ate: Sun, 10 Jun 2007 16:05:07 -0700
> rom: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
> o: Tesla list <tesla@xxxxxxxxxx>
> ubject: NST Shunt Removal
> Hi All,
> My 4.5" diameter coil spark lengths are far beyond a 12/60 NST capability.
> ttp://www.classictesla.com/photos/ba45/ba45.html
> nd these pics don't really show the lengths I've seen with this coil.
> The NST I use was modified by fixing some hv windings and removing 1/2
> f the shunts (back when I documented the NST depotting procedure. So,
> he 12/60 Franceformer is no longer a 12/60. At the time, I never
> inished the measurements on the NST. Well, I rebuilt my hv divider
> oday using 6 100Meg HV resistors (mfg p/n EX2G1006, $1.66ea). These are
> ade by Ohmite and good for 7.5KV each (I have 3 in series on each leg
> or 22.5KV at 300Meg). Anyway, following calibration, I tested an
> nmodified 15/30 Franceformer. All came out as it should. Here's the
> ata for the unmodified 15/30 NST.
> p=0.8 ohms, Rs=16230 ohms.
> OPEN CIRCUIT MEASUREMENTS:
> _pri = 124.1 V
> _pri = 0.74 A
> _pri = 24 W
> A_pri = 91 VA
> F = 0.27
> _sec = 15340 V
> SHORT CIRCUIT MEASUREMENTS:
> _pri = 124.0 V
> _pri = 3.83 A
> _pri = 39 W
> A_pri = 474 VA
> F = 0.08
> _sec = 25.74 mA
> 
> nowing that the hv divider is working well, I decided to unbolt the
> odified 12/60 and run it through both open and short circuit
> easurements. Here is what I found: btw, Rp=0.45 ohms, Rs=4660 ohms.
> OPEN CIRCUIT MEASUREMENTS:
> _pri = 124.2 V
> _pri = 1.53 A
> _pri = 50 W
> A_pri = 190 VA
> F = 0.26
> _sec = 13380 V
> SHORT CIRCUIT MEASUREMENTS:
> _pri = 121.3 V
> _pri = 20.3 A
> _pri = 428 W
> A_pri = 2457 VA
> F = 0.18
> _sec = 206.7 mA
> So, as you can see, this NST is no longer a 12/60, closer to a 13/200
> nd that explains the arc lengths being so good, or really, "not that
> ood" considering I am about 20" shorter than I should be for this power.
> Dr. Resonance was wondering why the little coil was doing so well and
> ad asked me offline. I let him know the NST was modified, but I didn't
> ave the data to give him at the time. I've probably pushed that NST to
> he brink of saturation, but, it has held up well, it just keeps on
> unning. It's reliability is a pleasant surprise considering what I know
> now" about the modifications.
> I took out exactly 1/2 the shunts. I_sec jumped from 60mA to 200mA (more
> urrent than I intended). I was hoping removing 1/2 the shunts would be
>  linear jump to 120mA, but that was just a shot in the dark. If I were
> o modify an NST again by removing shunts, I would only remove 1/4 of
> he shunts. 1/2 seems a bit much. This NST is more like a PT or
> ombarder now. I really don't know how long it will last. Last week, I
> ost an XBOX 360 and my main computer (video section on motherboard
> ommitted suicide). This was due to a small 2" coil that I ran without
> n RF ground. Big mistake. However, my NST Terry Filter smoked with this
> .5" coil Thursday. The coil and NST still run great, but the Terry
> ilter has some burnt resistors. Looks like I'll have to check all those
> OV's!
> Just thought this data might be of interest to anyone considering shunt
> odifications. I know those that happen to manage NST shunt removal like
> he fact they have (more power, baby!), but not everyone makes the
> easurements following the modification. And considering what I found,
> /2 the shunts removed might be stretching (or not depending on your
> iew of things).
> Take care,
> art
> 
> 
> 
> 
> 
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