# RE: Odd numbers

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Sundog -

Changing the voltage and not the watts can also be checked with the JHCTES
Ver 3.1 computer program. For example changing from 15KV/30ma to 4KV/113ma
will give you the same 450 watts with the JHCTES program but the spark
length will be reduced from 28.7 to 25.2 inches. This is based on empirical
data extracted from actual tests. However, the spark lengths shown will vary
depending on the construction of the coil.

If you use the joules equation you need the efficiency.
The efficiency for the 15KV/30ma (21000 peak) 450 watts
J = .5 * .01*10^-6 * 21000^2 = 2.21 joules for 28.7 inch spark
The input watts = 450/120 bks = 3.75 watts /break
This is 2.21/3.75 = .59 * 100 = 59 % efficiency

Assuming the same number of joules and efficiency
The 4000 volts (5600 peak) and 113 ma 450 watts
C = 2.21/5600^2 = .07 uf primary cap
This gives a 25.2 inch spark

There is not much difference in spark length at low wattages. Note that the
primary cap must be selected to agree with the primary voltage available. As
you say the larger currents will cause more losses because of the heating.
For this reason the 59 % I show for the 4000 volt coil may be lower. This
would give a lower spark length. Tesla coil design can get complicated and a
TC program can be a great help.

John Couture

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-----Original Message-----

From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, September 13, 2000 10:31 AM
To: tesla-at-pupman-dot-com
Subject: Odd numbers

Original poster: "sundog" <sundog-at-timeship-dot-net>

Hi All!,

I had myself an idea (Quick! Run and hide!), and plugged same #'s into
Wintesla.

I was looking at the J per bang figure, and since the more J you push, the
bigger the bang.  J=.5*C*V^2  Right?  Good.  That formula itself tells me
that if you maintain the same current (30mA in the case of my example
NST's), the higher voltage units have a better watts/joule 'rating'. IE, the
15/30 charges it's reso cap to ~4.9J (did I do that right?  sounds
reasonable, but it it *iss* wrong, it's consistantly wrong).
The same size bang, for a 4kv tranny takes ~115mA (aroung 450 watts) to do
the same thing, as it's charging a 76nf cap.   There's the basis.  Now,
let's say I want a bigger bang, say, 1J bigger. I'll just increase the
current.

The 15kv'er will see less of an increase, and the 4kv will see a fairly
chunky increase just to meet the same J per bang.  But each is still ~ the
same wattage.

For TC's, it's been said that a higher primary voltage is better.  i'm
guessing it's because a 5J bang at 4KV will sink a lot of current, but a 5J
bang at 15kv will have less current (I see the correlation of
voltage&capacitance of the tank cap there), for the same size bang.  Less
current=less heat=less losses in the gap.

Okay, it's beginning to click.  Now, when the gap fires, you get a healthy
dose of voltage/current into the primary.  What makes a stronger magnetic
field? A higher voltage or current, or is it just a combination of both (IE,
is a 12kv30ma energizing a selenoid of wire just as strong as a 100v/3.6A?)
Both are 360 watts.

Okay, if it's the voltage, I can see a 28kv1.5kva PT being worthwhile.  If
it's the current, I can see MOT's or a 7.2kv20-50kva PT being a solution.
On either end of the examples, quenching is a problem.  The 28kv system can
ignite a long arc just by it's potential.  The 7.2kv'er will try to powerarc
just by sheer current (several hundred MA at least)

A side-question:  The low voltage/high current approach would need a cap
with a good DT/VT, as it's got a *lot* of juice to move very quickly,
whereas the HV caps (smaller in capacitance by far), could be a bit "slower"
i guess.  ?

Soo, it all boils down to : more intense magnetic field by current or
voltage (if the total wattage is the same)?

Hmm..re-read it all, and It all looks to boil down to the total input
wattage.  Only real variable I can see is the V & I. I'll be researching
this on my own, but freely welcome comments :)