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Re: TC spark gap

Hi Alex,

At 05:00 PM 9/4/00 -0400, you wrote: 
> I am making my first TC. I am planing on using the "Terrygap"(
> http://users.better-dot-org/tfritz/terrygap.jpg) for the coil. My power supply is
> a 15/60 nst. If my calculations are right 60*.004 in =.24 in. right now I
> have a spark length if about 6/16 of an inch (.375). for a Jacob s ladder. 
> 1.What size xformer was the gap designed for because I am getting a spark
> with out any caps that is longer than the total gap length of all 60 pipes
> combined?

Each section of the gap has a large radius which gives it a higher voltage
breakdown than one would normally expect.  I used a 15/60 transformer with
great results.  I usually ran with the shorting bar about half to 3/4 the way
with that gap.  I think each section was 640 volts from memeory...  You may
want to use 0.006 inch spacing (maybe two thicknesses of paper) as later
results showed that to be a bit better.  That gape has great quenching and the
built in adjustability and safety gap are great!

My original gap is showing signs of old age and wild abuse, but it is still my
first choice for a static gap.  It's super good quenching could really pull a
lot of performance.

> 2 .Also can I mount it on  in glass or will the heat cause it to crack? And
> is the brake down voltage to low? 

The gap runs fairly cool with a 15/60.  I guess I would not worry too much... 
It "might" break on a long run so maybe some type of plastic or wood would be
better.  Hard to say...  With glass, breakdown voltage is not an issue at all. 
There are some nice newer versons but they are harder to make (machine shop). 
Spacing with paper and glueing with epoxy is just realy easy...

> 3.How does one calculate the max voltage of an AC xfomer? Do you just double
> the listed voltage.

If a transformer is rated say 15000 volts RMS or AC.  That is the equivalent
voltage that will heat a resistor to the same temperature as the same DC
voltage.  An AC signal has highs and lows so that is "sort of" an average
voltage (officially, it is the "root mean square" (RMS) voltage).  To make a
long story short...

Peak voltage = AC or RMS voltage multiplied by 1.414

1.414 is the square root of 2 which is sort of a "magic" number for such
calculations.  A very long story that gets into calculus and all... but just
trust me ;-))

So a 15kV transformer has a peak of:

15000 x 1.414 = 21213 volts

You should set the safty gap shorting bar to "just not fire" with the bare
output of the transformer.  That will be maybe 23kV so that the transfomer will
never go over voltage.



> Thank You 
> Alex Madsen