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RQ spark gap plans (fwd)
---------- Forwarded message ----------
Date: Sun, 3 May 1998 15:27:55 -0600 (MDT)
From: Chip Atkinson <chip-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: RQ spark gap plans
Greetings all,
Here is the text to the RQ (Richard Quick) spark gap plans. You can
download bot the text and a gif image to accompany the text from
ftp://ftp.funet.fi/pub/sci/electrical/tesla/misc/sparkgap.zip
--------------------------------------------------------------
This cylinder static gap was designed to quench 6-8 kv running up
to 1 kva in more or less continuous duty. It will quench 6-8 kv up
to 2.5 kva intermittent, depending of course on your run times,
three minutes being quite tolerable. These gaps are very functional
and can be easily moved from coil to coil. Complex gap systems can
be built up using more than one unit. These systems can provide
excellent power handling flexibility and efficiencies. It is
possible to tap the gap at the center electrode creating two equal
and parallel paths within a single unit. Two gap units wired in
this parallel configuration may be hooked in series for quenching
up to 1.2 kva continuous, or 3 kva intermittent.
These gaps can also be employed with great effectiveness when used
with a rotary gap. Units wired for parallel operation may be run in
series with a rotary gap. Excellent quench times can be achieved at
very low cost on medium powered Tesla coils in this fashion.
The copper pipe electrodes offer a large surface area to assist
in quenching. The electrodes are cooled by an air stream which also
removes hot ions from the gap during operation. The air stream is
provided by a 5-1/4" muffin fan mounted on top of the gap unit.
The gap is remarkably quiet, and the arc is shielded by the PVC
pipe eliminating the UV hazard.
Construction of a gap unit requires the following parts:
A five inch length of 6" PVC drain pipe
15" length of 1-1/2 inch hard copper water pipe
One end cap for the 6" PVC drain pipe
One 5-1/4 inch, high CFM, muffin fan
14 1/4" Brass machine screws with nuts and washers
4 #6 Brass machine screws with nuts
3 feet of good quality lamp cord
18" of thick wall vinyl tubing
Stiff epoxy
Cut the copper water pipe into seven two inch sections and polish
the pieces. Drill two holes in a line 1" apart and 1/2" from the
top and bottom of each section.
Drill two corresponding holes, larger than those drilled in the
copper pipe, into the PVC drain pipe. The holes in the copper pipe
should be snug for a 1/4" machine screw. The holes in the PVC pipe
must be loose, allowing play to properly gap the electrodes. Do not
drill all of the required holes into the PVC pipe at once, work
with one electrode at a time.
Mount the first electrode. Two 1/4" brass machine screws are used
with the screw heads inside of the copper pipe and the threaded
ends extending outside. Install a washer and nut on the screws and
tighten until snug but DO NOT OVER TIGHTEN. Measure out ~2-1/2
inches and drill two holes for the second electrode. After fitting
you may find it necessary to file out the holes before you can get
a parallel gap. Use a feeler gauge and adjust until you can set a
gap of .028 inches with the nuts snug. It is important that the gap
be equal and parallel up and down the entire 2" length of the
copper electrodes.
When the gap can be set, remove the first two electrodes and smear
a stiff epoxy on the back sides around the screws. Reinstall the
electrodes and snug the washers and nuts down, adjusting as
necessary for a parallel gap. It is important that the epoxy gushes
out around the nut and washer. As the gap is run over time, heating
and cooling will loosen the mounting nuts unless there is
sufficient epoxy on the threads to permanently affix them. Make
sure to wipe away the excess and thoroughly clean the screw threads
above the nut. The screws serve as the terminal posts and if the
threads are fouled with epoxy you will have to fight to get your
connections on and off.
Proceed with drilling the next two holes and fit the next
electrode. Gap as above. When you can achieve a perfect gap, remove
the electrode and bed it with epoxy. Check your gaps carefully and
frequently, once the epoxy sets you will never have to worry about
them again!
After all seven electrodes are installed, place the gap unit under
a heat lamp to speed the epoxy cure. Then assemble the blower unit.
Center the muffin fan on the PVC end cap and scribe a circle for
the fan cutout. Cut the circle out and drill four holes for the
muffin fan mounts. Mount the fan with the four #6 machine screws
and nuts so the air flows from the bottom of the gap unit up.
Slide the lamp cord through the vinyl tubing and solder the ends of
the wire to the muffin fan terminals. The vinyl tubing is important
to provide some protection from the high voltage present on the
exposed gap terminals, but do not rely on it. Route your 110 volt
line away from all high voltage points with nylon wire ties and
provide for line filtering when using the gap.
When the epoxy has set, mount the fan assembly on top, but do not
glue it into place. The top is removable for easy cleaning between
the electrodes with #600 or higher sandpaper wrapped on a shaved
down tongue depressor. I build a wooden or plastic tripod base to
set the gap unit on. The gap base should allow at least 3" of space
below the gap unit for airflow, I allow 4 inches.
The gap as sketched shows the installation of an arc shield between
the two end electrodes. This is important despite the fact that the
gap here is quite large. With a piece of 3/8 inch plexiglass glued
in this spot, gap units can be run together in series to quench
higher voltage power supplies without the arc taking the shortcuts.
When run with neons at 12 kv rms, two gap units are used and
all the electrodes are run in series. If higher voltage is used
(up to 25 kv) gap units may be added in straight series connection
providing your kva load does not exceed the individual gap unit
rating for long run times. Allow 1000 volts per gap between
electrodes (.028").
When more transformers are added to the coil, the capacitance is
increased correspondingly, input voltage remains the same.
Higher tank currents require that the primary arc be split into
parallel paths to cool and quench. To meet this requirement
additional gap units are added but all gaps are tapped at the
center electrode and the two end electrodes are connected together
with copper or aluminum strap. The second gap terminal is taken
from this point. The gap is now wired for parallel operation, it
will handle twice the current. A second unit is configured the same
way and added in series with the first. The resultant gap system
will handle twice the current at the same input voltage. For
highest "Q" all connections should always be made using both
available terminals from the tapped electrodes.
Quenching performance can be increased by mounting an air choke on
the gap base. This will act to prevent air from passing up the
center of the gap where it takes up little heat and fewer ions.
I use a piece of 3" or smaller PVC pipe set on the gap base and
passing up into the bottom of the gap just under the electrode
ring. This forces the air to pass through the electrodes and
between the gaps to remove heat and ions and improves the run time.
Performance may also be improved by fitting finned, cylindrical
heat sinks, available at the electronics surplus or many hamfests,
into the center of the copper electrodes. A little heat sink paste
here is helpful to assist in heat removal from the electrode and
preventing corrosion from the aluminum/copper contact. Oxides
formed by contact corrosion are poor heat conductors. For maximum
effectiveness the heat sinks should be cleaned of any coating at
the contact points. Finned heat sinks installed in this fashion
will dramatically increase the surface area of the electrodes. This
is especially true in gaps of this design using larger copper pipe
and bigger gap rings.
When running these gap units as part of a system with a rotary, all
gap adjustments are still made on the stationary electrodes of the
rotary gap. Insert one .028" static gap (distance between each
electrode in this unit) in series for every 2000 volts of line
input to the coil, then set the rotary gap adjustment so that the
coil system fires smoothly and reliably. Suppose your rotary system
has a 12 kv line input: every electrode on the cylinder static gap
unit is gapped at .028", and you need a total of 6 of these static
gaps in series with the rotary for the system to function properly
at 12000 volts. There is no limit to the number of parallel paths
that can be theoretically used, but two is the practical limit with
this design. Two cylinder static gaps hooked up for parallel
operation, and run in series with the rotary will provide excellent
quenching up to 2 kva continuous, 3.6 kva intermittent. Your rotary
will require a much smaller gap, and your quench time will have
dropped considerably. Your rotary will run cooler, your run times
will be longer, and your secondary spark will be better.
Another benefit of gap systems with a rotary is that the wear
caused by the hot arc is distributed among many gaps with a large
surface area. The arc at the rotary is both cooler and shorter in
duration, taking stress off of the stationary electrodes and
reducing wear at these critical points.
Gaps of this design using 1" diameter copper pipe can be
constructed as above to get 12 gaps into a cylinder ring of 13
electrodes. The 1" diameter pipe sections do not sink as much heat,
but if gapped at .028 -.030 inches a single unit will quench up to
15 kv rms from neon sign transformers banked up to 1.5 kva
intermittent. If the unit is constructed from 1" dia. pipe and the
electrodes are gapped at .056 -.06 the arc can be split down two
parallel paths (center electrode tapped) for a good quench time
with a neon power supply of 12 kv rms in the 1.5 kva power range,
this is of course intermittent operation but will use only one gap
unit. Using the flaired end of 6" pvc drain pipe will give enough
room to squeeze in all of the required electrodes and the arc
shield, but the result is the fan must be custom mounted, and may
have to be glued into place.
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Chip Atkinson
http://www.pupman-dot-com
--- If I can't fix it, I can fix it so it can't be fixed --
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