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Re: [TCML] Questions on grounding

Hi Dex,
I've never experienced such an affect. I suspect that some have maybe theorized that blowing air into the gap will blow out the spark if it's high enough velocity and volume to affect the quench. What I personally theorize is that when air is blown into the gap at high velocity and volume, the pressure within the space between electrodes is increased and thus increases the breakdown voltage (allowing the voltage to climb a little higher before breakdown is achieved and thus a little higher energy). This may appear as affecting quenching only, but I suspect it is mostly a change in energy. However, quenching would also be affected to some degree due to the change in energy as well as the intensely cool electrodes, lack of ions, etc. But that is assuming the supply is capable. 
I think for most reports of coilers doing this, they reported more 
problems than successes. The difference there may have been differences 
in supply current, cap sizes, etc.. up stream. For example, if someone 
is using a little 12/30 NST and going overboard on the air, then likely 
the gap will begin having problems even getting started and begin to 
breakdown very erratic and in that case lower performance. But if a pig 
is powering the coil, there is maybe a chance that the pressure will 
affect that gap as stated.

The term "overquenching" I can't really wrap my mind around and it 
really doesn't make sense to me in this case. I guess if there is a case 
where quenching at 2nd and 3rd notch performs better than 1st notch 
quenching, than one might be able to use the term "overquenching"? But 
that is not related to this scenario of forced air. There's a lot more 
involved in that type of situation regarding the system as a whole.

Just ramblings as I haven't tried super high velocity forced air myself. 
I've simply listened to what coilers have reported over the years.

Take care,
Bart

Dex Dexter wrote:

Bart and everybody,

Bit off topic question.
I have heard of the possibility so called "overquenched gap".
How strong must be an airflow through the static gap of a NST coil to observe the effect of the "overquenching"?


Dex


--- bartb@xxxxxxxxxxxxxxxx wrote:

From: bartb <bartb@xxxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] Questions on grounding
Date: Tue, 21 Apr 2009 18:14:57 -0700

Hi Joe,

12" to 16" is good improvement.


Don't increase the spark gap. All this will do is increase the breakdown 
voltage and can kill the NST. A new gap would be good and the hyperbaric 
gap (linked the drawing in a post last week) is probably the easiest to 
build. It's basically a PVC T-fitting with copper pipes inserted into 
the ends along with a brass fitting on each end. The air is forced up 
through the center hole in the T-fitting. For your 12/30 NST, you can 
max out at about 27", so another 11" is about all you can expect out of 
the 12/30 on a perfect day. I think in order to achieve that or even 
come close, a new blown gap would be needed. That's up to you of course. 
If you do end up adding a 2nd 12/30 NST in parallel with the 1st NST, 
then you basically have a 12/60. Max length is about 38" with this 
setup. However, your cap would be very near NST resonance and it would 
be best to throw a little more capacitance into the gap if you think 
about doing that (about 0.018uF to .02uF is what you want with a 12/60).

The toroid may actually be too big, not too small. Install a breakout 
point (anything you come up with will do). I have a 1 meter aluminum 
ruler that I use for a breakout point and I simply lay it on top of the 
toroid when I use it. This will allow the spark to breakout more 
consistently and it helps direct the spark to one side of the coil. 
Actually when your testing spark lengths against a ground wire or 
object, try using a breakout point as it gives a precise measurement and 
you will get far more strikes to the object. The breakout point can be a 
wire, a ruler, a rod, and some even go as far as to attach a 1/2" to 1" 
metallic sphere to the end of the rod. The rod should protrude out past 
the toroid edge by about 5 to 10 inches on your toroid size.

I don't think you need to lower the toroid at all. If the bottom of the 
toroid is 2" above the secondary, then it should be fine where it is.

Take care,
Bart



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