Science Buddies: "Ask an Expert"

In answer to your questions, we have 1 turn on the primary coil (rebar), and 971 turns on the secondary coil (PVC tube). There is wax paper inbetween each layer on the secondary coil as insulation.
The spark gap distance is set for the distance which you described (card width - very close together in other words).
It still chatters, but will not generate a spark. I know this is not very many turns, but after reading and doing the math I really don't want a 7th grader to be generating many more volts than than. Is that the problem?Do we not have enough turns to actually generate a spark, and only to create the chatter, or is there possibly something else wrong?
Thanks for your help by the way. We're at a loss.

If I read your post correctly, your setup chatters but the high voltage gap will not spark across even 1 mm.

I agree with Craig it is difficult to diagnose without seeing the apparatus, but I think the following questions should be considered:
1) Is the high voltage side carefully insulated? This includes the mounts for the high voltage leads for the spark gap. You would not see a spark if the two high voltage leads were already connected together by any conductive path, or if there is a short within the high voltage coil.

2) With only one turn on the primary circuit, my instincts tell me you may not be generating enough of a magnetic field to fully pull away the Neef vibrator arm to open the circuit. You could consider adding a few turns to the primary curcuit. While this will reduce the output voltage, it might make it work.

3) Are you using a capacitor across the Neef vibrator? This is also rather important to get good operation.

Please don't start a new thread for each question about the same project. Having everything in the same thread helps the experts understand all of the history.

I know this is not very many turns, but after reading and doing the math I really don't want a 7th grader to be generating many more volts than [that].

Well it is a little late for that. The project clearly called out the high voltage issues.

6 volts * 971 / 1 = 5826 volts. Even if you used 18 volts on the primary, you would just be getting to where dry air would break down. What is the relative humidity?

Then there is the problem of what constitutes a single turn on the primary with a large wire. It is extremely difficult to construct a single turn coil that will perfectly couple magnetically to give a unity turn ratio. The issues decrease as you add more equally spaced turns because the end boundary conditions become insignificant with respect to the coupling of the inner turns.

You could easily be in a situation where the coupling factor is 50% in other words 6 * (971 / 1) * 0.50 = 2913 volts.