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Re: Nathan's Problems Continue...





Nathan:

You don't need 250 watt resistors on a NST system.  The lowly 50 watt, 500
Ohm units work just fine and they only cost $4.50 each from Digi-Key.

Dr. Resonance


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Tuesday, January 11, 2000 10:29 PM
Subject: Re: Nathan's Problems Continue...


>Original Poster: adamsmith <adamsmith-at-Mediaone-dot-net>
>
>
>Nathan, enclosed below is all the advice I can think of for your
>situation.
>
>>Anyway, it ran pretty smoothly for about 10 seconds, and then blew out one
>>of my NST secondaries.  Poop.
>>It probably served me right though, because I didn't have a protection
>>circuit on the transformer.  I intend to build one soon, but a 1kOhm 250W
>>resistor costs $15 plus 2.50 shipping from the east coast, because
according
>>to Norvac Electronics in Salem OR, resistors that big don't really exist
>>over here in the pacific northwest...
>
>Where do you intend to insert a single resistor of that size?  If you
>plan on dissipating 250W continuously anywhere in your protection
>circuit, you have some serious design issues ;-)
>
>>I think one thing that will help is putting more turns on my secondary.
>>Performance seems to increase linearly the more turns I tap on the
primary.
>
>As you increase primary inductance, you lower the tank resonance.  Now,
>as you are lowering the tank resonance you are noticing that you get
>bigger sparks, suggesting that you are heading in the right direction.
>Now, if you're running out of primary turns (i.e. you're tapping on the
>outer turn), you still have several variables you can play with to. If
>you don't have the equipment to measure the inductance of the primary, or
>the natural resonance of the secondary, I would recommend trying the
>following, in this order:
>
>1. Start with only a static spark gap, conservatively adjusted to a
>setting where the gap ALWAYS fires right away, without ANY sputtering.
>This keeps operation at a safe level, and minimizes the chance of blowing
>stuff. As any good coiler will tell the beginner, you should NOT ATTEMPT
>FULL POWER UNTIL THE COIL IS IN TUNE. Sorry for the "yelling", but I only
>want to keep you from blowing transformers in haste.  You should also
>have a variac to ramp up power to the circuit, and do the tuning at half
>power or so.
>
>2. Start with a minimal top-load! I suggest a small 3"x12" or similar
>toroid.  With a small toroid, you have a good chance of finding resonance
>within the current range of inductance allowed by your primary, and
>getting a breakout will be MUCH easier. Your 7"x22" toroid is ambitious.
>You can probably get it to breakout when you get the coil running at peak
>performance, and properly tuned, but you're going to drive yourself crazy
>if you don't start small and work up to this.  When you find the
>resonance point with the small toroid, you will have a data point worth
>its weight in gold.
>
>>No air breakout yet, even with a needle stuck in the toroid.
>
>A pretty good indication of not being anywhere near the tuning point.
>>From my experience, when you have this situation you also have a low,
>weak flatulant kind of sound from the spark gap also, instead of the
>powerful hiss that you should have. Is this what you hear?
>
>>What can I do, though, to get a better ground continuity to the toroid?
>
>I would not lose sleep over the apparent DC resistance of path to your
>earth ground.
>
>>P.S. (You have all been so cheerfully helpful! What do I do next?? My
>>problems now are a bit too specific to check the archives, I think.)
>
>I would not say your situation is unique at all.  I think you are
>starting out pretty much the way all of us did--to ambitiously :-) You
>can't expect to hit resonance and the perfect operating point by
>accident.  Even if you build a system to nearly the exact specs of
>another working coil, it takes a lot of work to get it to operate
>perfectly.  I few millimeters of spark gap here, an extra turn of primary
>there, a slightly different coupling, etc... all can make the difference
>between 9" of spark and 40". The people who are getting 40"-60" inches of
>spark from a 15/60 didn't get there without some SERIOUS tweeking, lots
>of optimizations, and plenty of analysis and re-design of their systems
>(often with scopes, metering and CAD work).
>
>-Adam
>adamsmith-at-mediaone-dot-net
>
>
>