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Re: Several questions about coil.

In a message dated 12/28/99 6:48:39 PM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:

>  
>  I checked the value with a meter , and it's really 25nF. I think that
>  the dielectric can be not really good. I used a foil , that is used in
>  gardening , but I really don't know what it is (Chemical composition).
>  Can You give me any URL of web page, where can I find dielectric value,
>  and dielectric loss , of popular materials.
>  
>  > One thing is that you say you are
>  > only getting 4-5 inch sparks.  With 2000 watts input you should be > 
> getting
>  > much much longer sparks.  Sounds like the tuning may be far off...
>  > 
>  
>  I was tuning my coil not by counting the number of turns , but with
>  moveable wire , and 4-5 inch sparks is the best result :-(
>  I think that my coil is allright, but my power source may be wrong
>  (heating device instead of variac, and lack of power factor correction),
>  and im not really convinced , taht my capacitor is working properly.
>  
>  Also i want to ask You ,if you have any suggestions about sparkgap.
>  What kind of sparkgap schould I use in 2000W coil?
>  
>  thx
>  
>  Kamil Kompa

Kamil,

I have used a standard cylindrical static gap (referred to as a RQ or TCBA 
gap) up to 1500 kva.  This gap uses 6 to 8 sections of 1.0 to 1.5" copper 
water pipe about 4.0" long mounted to the inside of a 6.0" diameter pvc 
plastic pipe.  Mine have an end cap on the top end with a large hole cut out 
and a small fan mounted there.  They have plastic feet on the bottom to 
provide an air gap of about 1.0".  I believe some folks have used this style 
gap up to 2000 kva.  Gary Lau has very good results with a single forced air 
gap.

As I mentioned before, I believe your coil is not properly tuned.  I also 
think you are correct in that some of your problems have to do with how much 
power is really getting to the coil.  Is your transformer internally current 
limited?  If it is not, you really need to use inductive current limiting (as 
opposed to the resistive load of the heater) so you don't loose so much power 
across the ballast.  And of course, a variac would be a big help so you could 
bring the power up slowly, and tune the system at less than full power.  As a 
poor man's control system, you could use several oven heating elements or hot 
water tank heating elements in series with the transformer primary.  The 
heating elements are set up so that one is in series with the primary of the 
transformer.  (My oven elements are about 22 ohms each).  Then wire in 
several standard house light switches so as to be able to add one heating 
element in parallel with the first one with each switch.  So you turn on the 
power with one of these heating elements in the circuit, then gradually 
switch others in parallel until you get to the power level that you want.  
Maximum power would be with all switches on and all elements in parallel.  I 
have such a system that allows me to switch in 22 ohms down to 3.3 ohms in 
six steps.

Good luck, Ed Sonderman