Observations - Gaps and Arcs
From: terryf-at-verinet-dot-com <terryf-at-verinet-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Wednesday, July 01, 1998 4:28 PM
Subject: Observations - Gaps and Arcs
Today I made two observations I would like to pass on.
I use a series of copper pipe sections mounted on a straight piece
of wood as a spark gap. I made another last night that had three times the
spacing between the sections. The pipe diameter was larger but I don't
think that had much effect. I found that with larger spacing the quenching
was much worse!
7 spaces at 7 mil each with 1/2" pipe
3 spaces at 24 mil each with 3/4" pipe
The firing voltage in each case was about 7400 volts peak producing about a
The quenching of the new gap was terrible! The old gap almost
always quenched at the first zero current crossing. The new gap often went
through 5 nodes before it quenched (actually the system just ran down).
This strongly suggests that many very small gaps are much better than a few
larger ones. I think gaps less than 5 mil will clog up so there is a limit
how small the gaps can be. A picture of the old gap is in the report at:
I checked the tuning and all that but the problem seemed to be the gap.
This gap is easily adjustable and seems to run cool if the quenching is
By measuring the ringdown time of my coil, I can calculate the
equivalent resistance the secondary is seeing. Under low voltage and no
breakout conditions, the secondary rings down to half voltage in 29 cycles.
This suggests that I have about 270 ohms total in the secondary LC circuit
(70 ohms in the wire, skin effect, and the terminal is a shorted winding).
I then placed a small point on the top to get a small (~1 foot) streamer off
the top. The voltage was 260 kV and the ringdown to half voltage occurred
in about 5 cycles. This calculated (by computer simulation) to around a 1
This actually suggests much. In order to get maximum secondary
voltage, it is important to make the dimensions and surfaces of the
secondary so that they can contain high voltages without much leakage (we
all knew that :-)). This is probably much more important than trying to
reduce the secondary wire resistance. The corona losses are probably much
much higher than the wire resistance losses. If the coil is putting out
sparks, the secondary wire loss is probably not a factor. If the power is
proportional to the resistance, the wire is loosing only 0.027% of the
The science goes on.