Re: NST Shunt Removal (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 11 Jun 2007 17:56:09 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: NST Shunt Removal (fwd)

Hi Jim,

Ever measured what the current is now? Easy to do if your interested. 
The transformer is rated for "open circuit" voltage and "short circuit" 
current. So, short the two HV terminals through a digital ammeter and 
set the dial to mA (most of these meters are capable of about 300 to 500 
mA). Plug in the NST and read the output. The shunts are current 
limiting the NST, so this type of test is real easy for this 
transformer. You might be surprised at the short circuit current value 
as I was.

SAFETY NOTE: You must ensure there is a good connection between meter 
and hv terminals. If for some reason there isn't, then the output 
voltage would be felt across the meter and the meter would likely die. 
With a good connection, the hv side is shorted out through the meter and 
the HV is not present. If you want to test how the NST reacts, sounds, 
etc.. with the hv shorted, simply connect a piece of wire between both 
hv terminals and plug in the NST. You'll then get a feel for what to 
expect. After that, just connect the meter ready to read milliamps and 
ensuring you've plugged in the leads to the appropriate receptacle on 
the meter.

Take care,
Bart

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Sun, 10 Jun 2007 18:33:34 -0700
>From: Jim Mora <jmora@xxxxxxxxxxx>
>To: 'Tesla list' <tesla@xxxxxxxxxx>
>Subject: RE: NST Shunt Removal (fwd)
>
>Hello,
>
>I too modified a France 12/30 removing half the shunts and potting it a
>mixture of melted Vaseline and paraffin. It arcs a Really hot flame!
>
>Jim Mora
>
>-----Original Message-----
>From: Tesla list [mailto:tesla@xxxxxxxxxx] 
>Sent: Sunday, June 10, 2007 3:51 PM
>To: tesla@xxxxxxxxxx
>Subject: NST Shunt Removal (fwd)
>
>
>---------- Forwarded message ----------
>Date: Sun, 10 Jun 2007 16:05:07 -0700
>From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: NST Shunt Removal
>
>Hi All,
>
>My 4.5" diameter coil spark lengths are far beyond a 12/60 NST capability.
>http://www.classictesla.com/photos/ba45/ba45.html
>And 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 
>of the shunts (back when I documented the NST depotting procedure. So, 
>the 12/60 Franceformer is no longer a 12/60. At the time, I never 
>finished the measurements on the NST. Well, I rebuilt my hv divider 
>today using 6 100Meg HV resistors (mfg p/n EX2G1006, $1.66ea). These are 
>made by Ohmite and good for 7.5KV each (I have 3 in series on each leg 
>for 22.5KV at 300Meg). Anyway, following calibration, I tested an 
>unmodified 15/30 Franceformer. All came out as it should. Here's the 
>data for the unmodified 15/30 NST.
>Rp=0.8 ohms, Rs=16230 ohms.
>
>OPEN CIRCUIT MEASUREMENTS:
>V_pri = 124.1 V
>I_pri = 0.74 A
>P_pri = 24 W
>VA_pri = 91 VA
>PF = 0.27
>V_sec = 15340 V
>
>SHORT CIRCUIT MEASUREMENTS:
>V_pri = 124.0 V
>I_pri = 3.83 A
>P_pri = 39 W
>VA_pri = 474 VA
>PF = 0.08
>I_sec = 25.74 mA
>
>
>Knowing that the hv divider is working well, I decided to unbolt the 
>modified 12/60 and run it through both open and short circuit 
>measurements. Here is what I found: btw, Rp=0.45 ohms, Rs=4660 ohms.
>
>OPEN CIRCUIT MEASUREMENTS:
>V_pri = 124.2 V
>I_pri = 1.53 A
>P_pri = 50 W
>VA_pri = 190 VA
>PF = 0.26
>V_sec = 13380 V
>
>SHORT CIRCUIT MEASUREMENTS:
>V_pri = 121.3 V
>I_pri = 20.3 A
>P_pri = 428 W
>VA_pri = 2457 VA
>PF = 0.18
>I_sec = 206.7 mA
>
>So, as you can see, this NST is no longer a 12/60, closer to a 13/200 
>and that explains the arc lengths being so good, or really, "not that 
>good" 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 
>had asked me offline. I let him know the NST was modified, but I didn't 
>have the data to give him at the time. I've probably pushed that NST to 
>the brink of saturation, but, it has held up well, it just keeps on 
>running. 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 
>current than I intended). I was hoping removing 1/2 the shunts would be 
>a linear jump to 120mA, but that was just a shot in the dark. If I were 
>to modify an NST again by removing shunts, I would only remove 1/4 of 
>the shunts. 1/2 seems a bit much. This NST is more like a PT or 
>bombarder now. I really don't know how long it will last. Last week, I 
>lost an XBOX 360 and my main computer (video section on motherboard 
>committed suicide). This was due to a small 2" coil that I ran without 
>an RF ground. Big mistake. However, my NST Terry Filter smoked with this 
>4.5" coil Thursday. The coil and NST still run great, but the Terry 
>Filter has some burnt resistors. Looks like I'll have to check all those 
>MOV's!
>
>Just thought this data might be of interest to anyone considering shunt 
>modifications. I know those that happen to manage NST shunt removal like 
>the fact they have (more power, baby!), but not everyone makes the 
>measurements following the modification. And considering what I found, 
>1/2 the shunts removed might be stretching (or not depending on your 
>view of things).
>
>Take care,
>Bart
>
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