Re: New coil troubles

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <tesla111@xxxxxxxxxxxxx>

Hi Chris,

Your problem is likely tuning and coupling. There is more info needed to be 
completely accurate. I guessed at wire size to be #24. With toroid, the 
resonator should tune at 335 kHz. Thus, with your .058uF cap size, you need 
3.9uH of primary. I couldn't model your complete primary since it is part 
helical and flat. I did note that of you have 4 turns of helical and this 
coil would tune in at 4.7 turns, so it should tune in somewhere around the 
first "flat" turn which I believe is turn 5.

You don't mention the sec height in relation to the primary. So, "if" the 
bottom winding were even with the first bottom turn of the helical 
secondary, your coupling would be high, even with only 4.7 helical turns 
(0.163). Simply raising the secondary 1" will drop this value to 0.125 (as 
a reference since I don't know actual positions). Sparks breaking out of 
the center of the secondary indicate the voltage at the breakout position 
(be it a voltage node or whatever) is too high. Because of it's position, I 
suspect your out of tune.

I recommend positioning the secondary so the bottom turn is center to the 
helical and tune the coil at that position. Depending on your actual cap 
value, the inductance needed may be slightly more or less than 4.7 turns. 
You can adjust coupling higher for performance improvement after you are 
sure you are tuned in.

Take care,
Bart B.

Tesla list wrote:

> Original poster: "Christopher" <cpfortun@xxxxxxxxxx>
>
> Hi,
>
> I'm writing in regards to a new coil I recently constructed. The specs are 
> as follows : 9kv franceformer....180mA, SRSG, a total of 24 caps.....8 
> seriesed 3 legs paralled.. (.15MFD at 2000V each) making for a total of 
> .058MFD, the primary coil consists of 11 turns......the first four turns 
> are vertical and the other seven are horizontal.....I am using 1/4" soft 
> copper tubing "OD" and the spacing between the turns is 1/4", the 
> secondary is 3" "OD" with a total height of 24 1/2" with the magnet wire 
> wrap length meausuring 22 3/4"........on top of the secondary is a spacer 
> which holds the toroid a total of 3 1/2" above the secondary, the toroid 
> measures 19 1/2" by 4". The electrical connections are as follows : xfmr 
> is in parallel with the caps, on end of the caps is connected straight 
> into the primary coil, the other end of the caps is connected to the spark 
> gap (one side of the spark gap), the other side of the spark gap is used 
> for the tapping point of the primary coil, (The safety gap, secondary 
> coil, and strike rail are connected together as one source going to RF 
> ground). If there may be any questions that need further explaination in 
> regards to the mechanical or electrical setup let me know.
> Moving on to my troubles.......when I initially constructed my coil I 
> allowed for a 5" inside diameter between my secondary and 
> primary........which left a total of 1" spacing between these two. This 
> wasn't enough because I was getting sparks from my primary to my secondary 
> on the vertical turns. So I redid my primary and made for a 6" inside 
> diameter needless to say this fixed the problem and decreased the tapping 
> point. The problem now is that my streamers are extremely short, maybe 10 
> inches, and I am getting sparks that start about the middle of my 
> secondary which strike down to my primary. The tapping point has no effect 
> on the size of the streamers no matter where I tap it, they are the same l 
> ength. I tried raising the secondary gradually but has no effect on 
> eliminating the sparks from the secondary to the primary.....I either get 
> sparks or nothing at all. The spark gap is set up as 4 stationary 
> electrodes and 1 rotating electrode. I am also using a variac with this 
> system. After the spark gap has been turned on and operated up to full 
> speed, I slowly turn up the variac from 0 V to 120 V, this is the reaction 
> of the spark gap....all four will fire, then two will fire and them the 
> other two will fire almost instantaneously, then only two of the 
> electrodes will fire until I reach 80 volts and then all four will kick in 
> again and stay on up to 120 volts. Does this sound pretty normal for the 
> operation of it ? Anyhow that's enough for now.
> Any feedback in regards to the sparks from the secondary to the primary 
> and just the overall setup and operation of this unit will be greatly 
> appreciated :)
> Thanks,
> Chris F.
> <mailto:cpfortun@xxxxxxxxxx>cpfortu n@xxxxxxxxxx