Re: Of Resistors, First Light, and SparkGaps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Tesla list wrote:
> 
> Original poster: "Simon Yorkston by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <quantumx-at-ozemail-dot-com.au>
> 
> Hi all.
> 
> Well, the days has finally arrived, I'm ready for first light.
> Before I do, I have just a few questions.
> 
> 1] The 100W Resistors in the NST Protection unit. For RE. to the question,
> you might want to look at:
> 
> http://au.rs-c.dk/servlet/dk.stibo.module.ShowModuleServlet?moduleId=5124333
> 
> Although they are heatsinked, they get pretty darn hot quite quickly [~1
> min] to the point where they are almost too hot to touch.. Is this ok? If
> you look at the picture, you can see that there is not much space between
> the connecter and the heatsink. This is causing some problems; if I tap my
> sparkgap at too many gaps, it just arcs from connector to heatsink on the
> resistor. [This is despite insulating taps [which I didn't expect to do
> much] and HDPE [which I though would] Any Ideas? I have got some silicon,
> do you think that would do the trick?
> 
> 2] I have seen a list of things to do when preparing / running first light.
> I was wondering if someone could foward me a copy or something similar?
> 
> Thanks a lot
> Simon
> 
> PS> I'd like to take the time now to thank everyone on the list for all of
> their help. It has been really appriciated during the contruction process!

Simon,

As others have indicated, for high voltage work you really need to use
tubular power resistors (wire wound or non-inductive, on ceramic forms).
Because of the conductive aluminum housing, your power resistors are not
able to handle the high voltage spikes that these resistors are designed
to prevent from getting back into your NST. They flash over, defeating
their intended purpose. BTW, it is normal for these resistors to run hot
- often at hundreds of degrees. 

Here's a brief sequence of actions you can take to set up and tune the
system for first light:

1. Double check to make sure your secondary and strikerail (if used) are
both securely connected to your RF ground. Make sure that you have at
least 1" - 1.5" of clearance (all around!) between your secondary
winding and the innermost turn of the primary.

2. Close down your protective gaps. You can always widen them again
later. If you set them too wide initially, you may blow your NST.

3. Put a breakout bump or nail on your toroid to insure breakout at low
power levels

4. If you have the right test equipment, measure the resonant frequency
of the secondary/toroid by itself. With the secondary removed, adjust
the primary tap so that the primary LC circuit is adjusted to the
frequency of the secondary/toroid. If you don't have the proper
equipment to do an "instrument tune", set the primary inductance to the
estimated tap predicted by WinTesla (or similar design aid). 

5. Now install the secondary, elevating the secondary versus the primary
to reduce coupling. For a flat primary, set the bottom of the secondary
winding to be at least 1.5" above the plane of the primary. If you're
using a conical primary, increase the secondary height so that the
bottom of the secondary winding is 1" above the midpoint height of the
primary.

6. Now slowly ramp up power via a variac. Once the main gap starts
firing, "eyeball" the streamer length and power setting on the variac.
Look for any signs of abnormal arcing or corona between the primary and
secondary and fix before increasing power. 

7. Turn off power, move the primary tap outwards by 1/2 turn, apply
power up to the previous power level, and determine if the spark length
has improved. If performance improves, move out another 1/2 turn and
re-try. If performance decreased, decrease by 1 turn (and then 1/2 turn
per try thereafter). Repeat until you get maximum streamer length. If
you are about in tune and only using only a couple of primary turns,
your primary cap may be too large. If you can't bring the system into
tune even by using all of the primary, your tank cap may be too small. 

8. If you did find a point of good performance, repeat the above tuning
process but adjust by only 1/4 or 1/8 turn at a time to find the
best tuning point. Note: certain coils may not show a sharply
defined tuning point (such as systems with saltwater or ceramic caps, or
coils with low secondary "Q"). 

9. Once you've brought the system into proper tune, begin increasing the
power level while running the system in a darkened room. Look for any
signs of abnormal behavior (flashovers, abnormal corona, etc.) as you
begin increasing power. 

10. If your safety gap fires excessively before you
can reach full power, increase the safety gap spacing slightly. When
properly set and the system is in tune, the safety gap should fire every
now and then (once every second or two...). Continue to ramp up power,
fixing any problems, until you can safely run at full power. 

11. Now remove the breakout point and verify that system breaks out
properly. If the system won't break out, you may need to increase
coupling somewhat, or decrease the size of the toroid. Don't run for
extended times without breakout - re-use the breakout point if
necessary.

12. Slowly decrease the height of the secondary by 1/4" increments and
re-test, looking carefully for any signs of racing sparks on the
secondary by running in a darkened room. Continue to increase coupling
until you begin to see infrequent racing sparks. At this point increase
the height by 1/4" or 1/2" and the racing sparks stop.  

13. Remove the breakout point (if still attached). Determine if the
system will now break out on its own with the higher coupling. If not, a
smaller toroid, smaller radius of curvature on the toroid, or a larger
tank capacitor may be necessary. 

This should do the trick for first light. First-time coilers often
damage their new coils by using excessive safety gap spacing, excessive
coupling, improper tuning, or insufficient clearance between the
secondary and inner turn of the primary. If you immediately apply full
power with any of these problems you can damage one or more of your
coil's components.  

Best regards, and safe coiling to you!

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com