Re: First darkness :-(

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Matthew,

At 10:34 PM 12/8/2002 -0500, you wrote:
>Well I finally got to testing the coil for the first time this evening.  With
>probably the most disappointing results ever.  Nothing! Well the spark gap
>fired continuously but I got nothing on the toroid. Even after removing the
>toroid and retuning (well gueesstimating) I didn't even get a 1" 
>streamer.  I'm
>not quite sure what's wrong. Probably a combination of many things.

No worries!!  First coil runs never work the first time. ;-)


>First of all, my ground doesn't seem to be functioning.  I drove 4 2" 
>pieces of
>3/4" copper pipe into the ground so only about 3" were showing. I then
>connected these in parallel. I didn't test them until afterwards but found 
>when
>I put a light connected to hot and to my newly created ground, I didn't even
>get a dim glow. I didn't try to test the resistance but I would't doubt it's
>quite high.

You meant 2 foot rods (not 2").  Sounds like the ground resistance is 
pretty high but four 2 foot rods are going to conduct RF pretty good no 
matter what.  That is not the problem since some folks can get good 
streamers while forgetting to connect any ground ;-)  Pour water on the 
ground rod area for added conductivity (ice can't hurt :-)).  Don't use 
salt water since it will kill the grass or whatever in the area.  Double 
check the wires and connections to be sure it really is connected.

>I don't know why those pipes aren't working. I would think they're
>quite below the frost line (I live in Massachusetts so the ground is frozen
>here).

I guess I would double check the wiring and connections since I and 
surprised too.  But odder things have happened...


>Here are the spects of the coil:
>variac 140V output at high
>12/60 nst
>greg filter
>geek group cap (8 in series)
>spark gap air blast one gap (probably one of the main problems)
>primary, flat, 10" inner diameter 15.5 turns with .2" between turns
>second external tap primary. 4 turns with 1.5" between turns 18" diameter 
>helix
>(I tried bypassing the external tap primary as well as using all of it)
>secondary, 4.25" outer diameter, 28awg magnet wire. 22"
>Toroid, 6" dryer pipe, 29" outer diameter
>Tuned with toroid secondary resonates at 120kHz
>Primary resonates without second tuner at 120kHz as well
>(both tested with oscilloscope)

That all sounds great.  should be doing like three foot arcs.  Something 
basic is wrong...



>I think my first problem is a coupling problem between the primary and the
>secondary. I've got over 4" from inner turn primary to bottom of first turn
>secondary and I think the coupling factor is completely off. Unfortunately I
>don't have anything to measure inductance at my house so I'd have to bring it
>to MIT's circuitry lab to test it and it's quite a hassle.

Use this simple DOS (old operating system before windows, but still works 
fine with XP...) based program that is more accurate than coupling 
measurements anyway:

http://hot-streamer-dot-com/TeslaCoils/Programs/MANDKV31.ZIP

http://hot-streamer-dot-com/TeslaCoils/Programs/MANDKV31.PDF

>I think a good
>solution might be to make some more windings for the inside of the primary 
>and
>just solder the end of it to the current primary so I reduce the distance to
>the secondary at the same time as lowering the resonate frequency of the
>primary so it's a bit below the secondary to make up for the difference 
>caused
>by the ion cloud.

First I would say that the primary to secondary tuning is way 
off.  However, it sounds like you have measured that pretty well (but could 
you have tuned to a harmonic and not the true Fo frequency).  I didn't 
crunch the numbers for your coil but you should be putting in 900 watts and 
it has to go somewhere...  Is the spark gap really loud!!  If something is 
not tuned right, that is where the power should be going.  Nothing else 
should be getting hot or anything.


>I also think my air blast gap probably isn't very sufficient. I thought it
>would be ok since I just wanted to get a preliminary test with it.  It's two
>flat head screw driver bolts blasted with a fish tank air pump. Yes, you can
>laugh, I know it's mostly useless but I just wanted to try it. I think 
>next I'm
>going to try a multi gap using 3/4" copper tubing. That seems the most
>successful easy way.

A better spark gap may help a lot.  Use less sections and wider spaces for 
something like this or an RQ gap:

http://hot-streamer-dot-com/TeslaCoils/Misc/terrygap.jpg

Don't spent over 90 minutes making it ;-)


>A third and final problem that I see other than the ground is the toroid is a
>bit oversized for that nst. It's just too big.  I have another capacitor bay
>that I'm going to use for my next coil and I'll get another 12/60nst. That
>should put out enough power for that toroid but unfortunately right now it's
>just not very good.

Big toroids should not hurt anything as long as you can tune for it.  You 
might want to put a thin wire sticking out on it to help with tuning and 
trouble shooting.  The thin wire will break out into sparks very easily and 
is a sensitive indicator of what adjustments help and hurt.


>I'd appreciate any comments anyone has about my problems and preposed 
>solutions.

Give it some time and we'll get it going just fine ;-)  My first thought is 
always tuning when the sparks are super short like 1 inch.  Check all the 
wiring and be sure nothing simple was wired wrong.  Test many different 
points on the primary for tuning with the wire on the toroid and see if 
there are "sweet spots".  Start at 15 turns and work your way in 1/2 turn 
at a time.  I am not sure where you meant the primary is tapped now but you 
should be out in the 12 turn area.  If you only have "4" turns, that is way 
too few...

Cheers,

         Terry



>Sincerely,
>Matthew Morrissette
>MIT Department of Eletrical Engineering/Computer Science
>Undergrad