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Spark Joggers
Subject: Spark Joggers
Date: Sat, 3 May 1997 20:18:36 -0400
From: "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To: "Tesla List" <tesla-at-pupman-dot-com>
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Re: Ruminations on Gap geometry
> Date: Saturday, May 03, 1997 2:46 AM
>
> Subject: Re: Ruminations on Gap geometry
> Date: Fri, 2 May 1997 10:33:46 -0400 (EDT)
> From: DavidF4797-at-aol-dot-com
> To: tesla-at-pupman-dot-com
>
>
> Greetings all
>
> Reflecting on the post a while ago about the difficulty in getting a RQ
> gap
> to fire initially, it has occurred to me that the same thing has
> happened
> with my smaller table top systems verses as the larger (higher power)
> ones I
> have built. Reviewing my experience with a number of gap configurations
> that
> I have tried while experimenting it seems to me that the Richard Quick
> style
> gap (several coper tubes/gaps in parallell) seems to work great for
> medium
> medium - somewhat higher powered - coils (15KV-at-60/120ma). On small
> coils
> (6kv-at-20/40ma), however, it seems that the long copper tubes in the RQ
> style
> gap cause a certain "reluctance" in first fireing that is not as
> apparent as
> when smaller (say1/4in) tungsten rod is used end to end (for the same
> number
> and spacing of gaps). This, I suspect, has something to do with the
> larger
> surface area of the smoth copper pipe creating more of an inhibition to
> initial breakdown of the air between the cylinders. The chart below,
> posted
> a few days ago implies this issue. Is this phenomenon due to Inter
> electrode "E" fields perhaps? Radius of curvature, etc? And might this
> have
> sometning to say for general recommendations for gap styles in higher
> verses
> lower powered systems? Any thoughts on the matter?
>
> -----------
> Chart showing the gap voltage for needle points, and spherical
> electrodes of
> 2.5, 5, 10, and 25 cm. of possible interest here, :
>
>
> KV 2.5cm 5cm needle
> ----------------------------------------------------------------------
> 5 0.13 0.15 0.42cm length of spark gap
> 10 0.27 0.29 0.85cm
> 20 0.58 0.60 1.75
> 30 0.95 0.94 2.69
> 50 2.000 1.71 5.20
> 100 4.77 15.5
> 300 54.7
> ------------------------
>
-SNIP-
> -DavidF-
David,
Thanks for the table of breakdown voltages. Are these for DC or AC or
what?
Source of information?
You are right in surmising that the radius of curvature of the RQ gap
electrodes will retard initial firing until a certain critical voltage
is
reached. This is actually exactly what we usually want. The problem
comes
when there are too many gaps or too far apart. It is often useful to
have
at least one of the series gaps easily variable, with the others more or
less fixed. In many of my systems I have had the spark gap somewhat
removed
from where the secondary coil is located. While this arrangement is more
lossy, it does allow the gap to be varied while in operation.
In a low power system the RQ gap will work fine, but the spacing between
gaps may need to be lessened to insure initial firing. If you find that
initial firing is a major problem, then you might want to add a spark
jogger. You can implement a spark jogger in many different ways... the
exact implementation method is not important. The spark jogger works by
allowing you to temporarily short out or lessen the gap size of one of
the
gaps. As soon as the other gaps fire you can disengage the spark jogger
if
you want. Once the gaps start to fire, the circuit will experience peaks
that will keep it going. My joggers in their simplest are just a
variable
gap that I can adjust via an insulated handle while the coil is running.
Any kind of moving gap will automatically give you spark jogging,
because
the total length of the spark gap is constantly changing. I have used
really dumb rotary gaps that were made from hard disk platters. They
were
actually more like automatic spark joggers than what we normally think
of
as regular rotary gaps. These spark joggers run at *low* speeds compared
to
a real honest to goodness rotary. But they *DO* have their place, and as
spark joggers they work quite admirably and automatically.
For those that are interested in building rotary spark joggers, I use a
large hole punch to cut a ring of half circles equally spaced around the
periphery of the platter. The diameter of the cut circles is not
critical.
I have used circles with a diameter of from 1/4" to 2". I have used
platters from 3 1/2" and 5 1/4" and even 8" hard drives. You can spiffy
them up any way you want, but I do nothing to them other than cutting
the
half circles. Many of my contraptions look rather ugly, but they work,
and
that is my bottom line. I do NOT try to use the original motor drive.
But I
do use the assembly because of the BEARINGS that I then get for free. I
drive the assembly using an external motor and a belt. The belt must be
long enough to get the external motor away from the spark jogger disk.
ANY
kind of motor can be used. Sometimes I use flat belts, sometimes I use
these big "O" rings. Whatever I have and works I use. Don't be too
fussy. A
spark jogger is not a precision device by any means. Or, at least it
doesn't have to be. I have the rotary part mounted on plexiglass to
isolate
it, and I have more or less fixed gap studs located 180 degrees apart.
But
there is nothing wrong with using any other spacing. Whatever works,
guys!
Hope the concept of the spark jogger helps someone out there.
Fr. Thomas McGahee