Re: Primary to primary sparking?

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Chris,

On 31 Mar 2004, at 17:36, Tesla list wrote:

 > Original poster: Chris Roberts <quezacotl_14000000000000-at-yahoo-dot-com>
 >
 >
 > Hi everyone,
 >
 > I just got the coil out to do some pictures, along with trying it out
 > without a breakout point at the top. It seems to not like that, seeing
 > as it had plenty of racing sparks, primary to secondary flashovers,
 > and other problems. I guess it is a result of a higher breakout
 > voltage?

And possibly the couping between primary and secondary being too high.

  Anyways, during one of these pictures, the coil flashed
 > brightly with a huge mean sounding spark. I shut it down and took a
 > look. The spark seemed to occur between the primary tap and the next
 > outside winding, seeing as that's where the scorch marks are. So why
 > would the coil want to do that? Shouldn't the tap and the primary be
 > at the same polarity? Even if they were, wouldn't it be easier to have
 > the current go around one more turn instead of blasting through the
 > air? Whenever I fix this thing from sparking in one spot it starts in
 > another... except for all off the top. Is that so hard for it to do?

To answer the points in order: judging from the photo, I'd say the
spark was tracking along one of the support insulators.? There aren't
a lot of turns either. I'd infer that the volts/turn is pretty high.
There is of course a voltage difference between each primary turn and
in fact the polarities are not the same relative to one another.
Inductance and a possible lack of spacing between turns or possibly
some dirt of the support is the reason why the spark would occur
where it did. Voltage distribution across the primary increases as
one moves from the inner to outer turns as the outer turns have more
inductance than the inner turns. You are dealing with a situation
where the coupling is not stunningly tight. If it were, the volts per
turn would be equal as it is in a tightly coupled transformer.

Malcolm

 > Oh well, it at least made the ! photo look that much better! =D
 >
 > <http://hot-streamer-dot-com/temp/P1010077.JPG>http://hot-streamer-dot-com/tem
 > p/P1010077.JPG
 >
 >
 > -Chris
 >
 >
 >
 >