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Re: SPARK GAP BIAS TECHNIQUES

Hi Barry,

At 12:47 AM 03/02/2000 -0500, you wrote:
>Hi Marco,
>    Zelnick (sp) conducted experiments in the early days of radio with spark 
>gaps.  He found that if the spark gap was biased with a DC voltage the 
>damped wave train of the discharge never crossed Voltage zero.  This made 
>the spark gap very efficient.  One of the requirements for producing this 
>condition was the use of a current limited transformer.  You are correct 
>that there may be no difference between a DC supply and a current limited 
>Neon sign transformer but there may be a difference between a DC supply and 
>a pole pig transformer if Zelnick's experiments are valid.  
>
>
>Cheers,
>
>Barry
>
 
It is indeed true that "if" you could supply DC current to the spark gap,
it would not "go out" during the zero current (not voltage) crossings and
the efficiency would be improved greatly.  Easily said ;-))

So you need a 500++ amp current source that can withstand 20 KVAC in the
off state and be quickly (mS) turned on.  It must be isolated so that the
current would only flow through the gap and not mess (or burn) everything
else up.  It would be nice if it worked more than once ;-))  Gap heating
and wear would be much greater.  I have studied this and looked for such a
device.  I never found one even close with the exception of some
dramatically expensive devices using solid state optically fired SCRs such
as are used in the HVDC power industry.  Far easier to simply get another
NST ;-))

A capacitor with a resistor across the gap may be a possibility though...
Basically you would need to provide a high current pulse for the duration
of the gap's on time.  However, the power supply to feed such a cap would
probably be best used to charge the tank cap if more power is the goal.
Basically, you would be turning the gap into an intermittent arc welding
flame.  Bad for the gap and the power going into the gap would basically
contribute zero to the output other than the efficiency improvement.  Since
the gap looses about 50% of a coil's power you could only hope to double
the arc power for a 40% arc length improvement.  However, a 20kV cap
supplying 500 amps for 100uS at 120BPS works out to a cool 120kW!!  Almost
100 times the coils original power...

Another possibility is to have another tank circuit across the gap that
would fire in such a way so the current does not cross zero (the design is
left to the reader ;-))  However, the power going into that circuit is
again wasted for the most part.

I never could figure it out but don't let that stop others from thinking
about it.  You really only need to maintain a plasma in the gap so maybe
none electrical means would work...

Cheers,

	Terry