[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Primary coil configuration

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
A properly designed coil does not produce racing sparks. Setting the sec coil above the horizontal plane of the pri at the correct distance produces a correct design.
When you approach the "racing spark" mode it's because you had your sec too low to begin with. If you're doing a new design, start a bit higher than you expect and run it up and down with a simple screw type brass threaded thru a brass plate. The screw is hooked to a DC motor with a flexible shaft drive --- Dremel tool or even a tight tygon tubing will work. Run it slowly down until you can peak the spark. Go down 1/2 inch below this amount to check for a longer spark and then raise it up again. Now measure it. This is the point at which you hit optimum spark output which is really what we are trying to do here in the first place. Absolutely no need to produce racing sparks and then later elevate it. Once the damage is done --- it's done and only rewinding will cure it to a "like new" state again.
I've done this with many different sizes of sec. For a 4 inch size, which is what the experimenter was using, approx 1.25 inches is perfect and will not produce racing sparks. With a 6 inch size sec use 2.25 inches above the pri. No racing sparks, no damage, and no --- running the sec any lower will not produce any output gains at all. 

Dr. Resonance




Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Increasing the coupling until racing sparks occur, then backing off, is
the only way I have ever heard of to set the coupling.  Since the exact
mechanism responsible for racing sparks is still unknown, we are unable
to predict the coupling threshold at which they'll occur.  As setting
the coupling much lower than that threshold will degrade performance, we
strive to keep it as high as possible.  Some may consider it "horrible
engineering", but it's the best that can be done.   How do you propose
to determine that threshold without ever crossing it?

I agree that running a coil with racing sparks with reckless abandon
will permanently damage the secondary, but I think most of us have
briefly coupled too high, seen the sparks, backed off, and have had no
further trouble.  Or are you suggesting that a brief racing spark will
permanently lower the critical coupling threshold?  An interesting and
reasonable suggestion, but very difficult to prove.

I don't know that it's ever been conclusively demonstrated that any
secondary sealing technique will render it invulnerable to racing
sparks.

Regards, Gary Lau
MA, USA

> Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
>
> Someone advocated adjustment until racing sparks occur and then
> backing off. This is horrible engineering.  Once a spark punctures a
> solid insulation it does not "cure" or repair itself.  Once the
> damage is done it is permanent unless the coil is rewound.  You can
> back off the coupling to reduce sparkover, but then you always have a
> weakest link in your coil system. Properly sealing the sec coil and
> then not puncturing it will produce a long lasting coil.
>
> Dr. Resonance