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Re: stun gun/ Tesla coil?
[NOTE: If the stun guns are indeed non tesla coil circuits, the discussion
should mosey over to Steven Roys' HV list. -- Chip ]
----------
> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Re: stun gun/ Tesla coil?
> Date: Friday, January 17, 1997 12:58 AM
>
> Subscriber: rickh-at-ghg-dot-net Thu Jan 16 22:56:13 1997
> Date: Thu, 16 Jan 1997 20:06:06 -0600
> From: Rick Holland <rickh-at-ghg-dot-net>
> Reply-To: rickh-at-ghgcorp-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: stun gun/ Tesla coil?
>
> Tesla List wrote:
>
> >
> > hello,
> > I took apart a stun gun (100,000v) and I was wondering if the
coil
> > in there was a Tesla coil? How can they take a 9v battery and produce a
> > spark big enough to jump 2 inches? And I noticed they had a simple
spark gap
> > arrangement also set up in there.The instructions say to only run it
for
> > about three seconds or it will burn up. Is there a way to maybe pulse
the
> > switch to make it run continuosly? If anybody could help I'd sure be
very
> > appreciative. Thanks a lot.
> > Dave Edwards
>
> --
>
> Stun guns use a very basic approach to the Tesla Coil (which never quite
> reaches it), in that a low voltage is oscillated at a high frequency,
> fed into a step-up transformer (the high frequency requires a much
> smaller transformer using a ferrite core), filtered, and delivered to
> pointed output terminals. Some use a capacitative discharge system which
> requires a high voltage trigger; normally a small neon tube. This is the
> first I have heard of that uses a spark gap... perhaps I am falling
> behind the times.
>
> Rick Holland
>
> The Answer is 42
I have built a few of the stun gun circuits for use in various high voltage
experiments. The battery voltage is converted to a pulsating dc using a 555
timer which drives a small transformer -OR- a "ringing oscillator" circuit
is used to step the low battery voltage up to a couple of hundred volts.
This medium voltage is rectified and stored in a capacitor. When the
voltage reaches a certain critical value a trigger circuit is used to fire
an SCR or TRIAC. The trigger is often a neon bulb or a device called a
DIAC. Both of these devices turn on at one voltage and only turn off when
the voltage becomes substantially lower.
When the trigger circuit reaches its critical value, current is dumped into
the control lead of the SCR and then the SCR goes from a non-conducting or
blocking state to a conducting state. The medium DC voltage previously
stored in the capacitor is then dumped into the primary of the coil.
The secondary develops a high voltage due almost entirely to magnetic
action. There is little or NO resonance involved, so it is not really a
Tesla type circuit. It DOES ring, however, but this contributes little to
the overal high voltage. The stun guns usually have TWO coils wired in
anti-parallel so that each secondary produces a different polarity during
discharge. (The actual high voltage goes through a few polarity reversals
as the circuit rings a little, but it is the INITIAL pulse that causes the
snappy white spark).
As to the spark gap mentioned in the original posting, I am aware of two
types of spark gaps used in stun guns, but their purpose is NOT the same as
that of the spark gap in a Tesla coil.
There is almost ALWAYS a high voltage spark gap located near the output
terminals. It serves two purposes. The first is that it limits the maximum
voltage across the secondary coils in much the same way that we sometimes
protect our beloved Neon transformers by using a safety gap. Without this
safety gap the output spark could easily cause the tight wound secondary to
break down. The secondary, by the way, is a multi-layer type. There is very
tight coupling to the primary.
The second purpose of this spark gap is that it shoots big sparks and makes
lots of noise, and lets an agressor know that you are armed and dangerous!
The other type of spark gap is usually in the form of a high voltage
capacitor with a slot cut across the top. This is often placed across the
PRIMARY to prevent the voltage produced in the primary during the magnetic
field collapse from destroying the SCR. In a 300volt primary circuit the
reverse voltage produced at the PRIMARY can reach a couple of KiloVolts!
When all else fails, try something else!
Fr. Tom McGahee