Re: [TCML] Building my first tesla coil

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Jeremy,

I was going to send this last night (but our internet cable was torn
down thanks to our city trucks driving down the road with booms
elevated). It was finally repaired, but only as a couple hours ago.
-----------------------------------------

If the transformer has "ratings", use them. 1.5 x the Cres expected of
the transformer is right for the static gap coil. An RSG coil using a
synchronous RSG would be LTR at near 2.5 x Cres. But that's something
altogether differnt. The rational is based on the resonant rise. Maybe
easier to understand if we say "lack of resonant rise".

As Gary mentioned regarding static gaps; the spark gap width setting is
critical. It will determine the voltage at which breakdown occurs at the
gap (if it's set for 15kV breakdown, then at 15kV it will conduct
assuming no other influences that would lower the breakdown voltage).
The cap value used as the tank capacitance determines the overall bang.
Know that a transformers expected Cres value varies a little. However,
the result of the transformer characteristics with the 1.5 x Cres
expected value for LTR operation in a static gap is a matter of bps. If
you are closer to Cres than you expected, the gap will simply charge
faster and reach breakdown voltage sooner resulting in a higher bps. If
you are further away from Cres, the opposite occurs. In any event, the
gap determines the breakdown voltage and thus serves as the voltage
limiter (doesn't allow the NST to charge any higher than the gaps arc
voltage).

If the cap is 150% beyond the Cres value, then the voltages lower from
the Cres value, but it goes similarly for STR or LTR. Think of it this
way: If your cap is resonant at 10uF, then at 5uF it is (Cres x 0.5) and
at 15uF is (Cres x 1.5). Both have equivalent voltages. Imagine a bell
curve with Cres x 0.5 (this is the left side of the bell curve = maybe
15kV). Now imagine the same bell curve but equivalently at the same Y
level as the first, but to the right of the bell curve (again 15kV).
This is the Cres x 1.5 point. The left side is STR (smaller than
resonant) and the right side is LTR ( larger than resonant). Both STR
and LTR are equal in voltage levels away from Cres (which may be 30kV).
If the transformer will die at 20kV, you certainly want to be either STR
or LTR with your cap value to ensure the voltage never increases beyond
the transformers insulation breakdown level.

So, when we say 1.5 x Cres is recommended, it is because it is largely
outside of transformer resonance (enough to prevent the transformer from
having high voltage insulation failures) yet it is also a high energy
bang (as opposed to a low energy bang in STR mode). STR can do well. Bps
is the bridge between STR and LTR. In some cases, STR is amazing and
rivals any LTR coil. But, it's easier to go LTR if your using an NST
transformer. STR requires more attention to the gap to make higher bps
efficient (more attention means trial and error until you find what
works well). When you upgrade to pig status and upward, STR is the norm
(because LTR just gets too big and too expensive). But for low NST
currents, LTR does come in handy.

Take care,
Bart




Jeremy wrote:
> ok, i've kind of given up on precisely measuring the NST specs, i'll just assume it's 15kV 30mA since those are the closest reg specs. Now i have questions on the MMC. I have heard from sources that a larger than resonant bank of about 150% is recommended can anyone here confirm this as well as the rationale behind it? They claim that it protects the components from HV spikes though i'd tend to think the contrary since a larger bank accumulates higher voltage and current. The last thing I want to do is fry my NST.
>
>   
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla