Re: NST Shunt Removal (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 11 Jun 2007 17:40:13 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: NST Shunt Removal (fwd)

Hi Dennis,

Removing shunts reduces the magnetizing current limit and more current 
is allowed to flow. Increasing current increases the temperature in the 
low voltage windings and the ability to run "continuously" without 
meltdown is decreased. So yes, an NST is more susceptible to failure as 
a result of heat in the primary winding "if" it's run long enough. As 
Dr. R mentioned, you can run the core in transformer oil to help offset 
the increased heat.

Removing shunts is the easy part. Getting to them is ridiculously hard. 
The only reason I took on the task was because I had killed the 12/60 
(overvolted one of the hv windings) and I wanted to at least once depot 
an NST. Only after I depotted and fixed it, did the thought even occur 
to me to remove some shunts.

Take care,
Bart

Tesla list wrote:

>---------- 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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