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StevenCaton

Wed Jun 10 2009, 06:25PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

As far as spark length goes, would adjusting the variac up really make a significant difference?

Don't bother turning the variac up past 120VAC right now. If your system is only making 10 inch sparks, when your power supply should allow you to go much closer to 30+ inch sparks, turning up the variac makes no sense right now.

is there a way to calculate the change in output wattage if i change the input voltage?

You mean output wattage of the variac itself? Lets say it pulls 3 amps at 120VAC. So that's 360 Watts. If you crank it up to 135VAC and it now pulls 3.5 amps from the line, its 135 X 3.5, which is 472.5 Watts.

Blitzorn

Wed Jun 10 2009, 11:38PM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

no, i mean if i put 472.5 watts (or whatever, anything other than 360 watts) into the NSTs, how will THEIR output change? that was the intended question.

Herr Zapp

Thu Jun 11 2009, 02:13AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzhorn -

Without digressing too far into the topics of Watts vs volt-amps, NST magnetic shunts & core saturation, or the inability to "put" watts into anything, here are some thoughts on increasing the power input into the primary circuit:

1. If you increase the output voltage of the NST, and increase the total width of the (static) spark gap, the primary cap will charge to a higher voltage before the spark gap fires. As the energy stored in a capacitor is proportional to the square of the voltage across the capacitor, increasing the voltage even slightly can significantly increase the energy the capacitor dumps into the primary circuit every time the spark gap fires ("bang size").

2. If you increase the output current of the NST, it can bring the capacitor to full charge in a shorter time period. With a static spark gap, this will usually increase the break rate, which will increase the power (per unit of time) being pumped into the primary circuit. You'd think that a static gap could only fire at some multiple of the AC line frequency, but actually it fires quite chaotically.

Regards,
Herr Zapp

Blitzorn

Thu Jun 11 2009, 05:46AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Herr Zapp -

Excuse the slip - you're right, it's proper to use VA in this case, but the conceptual object is the same. Also, the distinction between putting "watts" of power into something and establishing an electromotive force that draws a certain current that is measured in watts is a bit nit-picky for this purpose, but the devil is in the details, after all. One detail i don't know much about is this particular model of NST's interior construction, so knowing when output levels out is really a matter of impirical testing.

1. Simple enough. More voltage in, more voltage out, more power, more bang, more fun. If it's any indicator of the capacitor's ability, the glass is quite cold to the touch after use, but even if heating is a sign of overstress i'm cautious enough to not assume that just because they are chilly doesn't mean they aren't lethally loaded and possibly already running at maximum load. This will bear further study.

2. This is where my understanding falters. All i can glean about current is that it varies based on many factors, and in this case, as i understand it, the increase would be due simply to the higher VA input being transformed proportionally. I'm ready to be corrected on that one xD

This still, although helpful, hasn't really answered the question, or if it has i haven't taken care to make sure i know exactly what i'm asking. just to clarify, if i move the variac tap up to 135VAC output, will it increase the voltage and current output of the NSTs?

Herr Zapp

Thu Jun 11 2009, 06:01AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzhorn wrote:

"....if i move the variac tap up to 135VAC output, will it increase the voltage and current output of the NSTs?"

In a nutshell, yes.

This exact topic was recently discussed on the TCML, and Bart Anderson performed some voltage and current measurements on a 15/30 NST with input voltages from 10-150V.

The resulting open-circuit voltage graph can be seen at:

And the resulting short-circuit current graph can be seen at:

Your 7.5/30 NSTs should respond to increased input voltage in a similar manner.

Check out the thread "Toroid Question" on the TCML where there are a number of posts discussing this topic.

Regards,
Herr Zapp

Blitzorn

Fri Jun 12 2009, 02:15AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Oh cool, thanks much for the clarification :)

I think this thread has performed its purpose at this point, considering the project as stated is now complete and the proverbial ball is undeniably revolving on a horiontal axis perpendicular to its direction of travel.

StevenCaton

Fri Jun 12 2009, 04:33AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

the proverbial ball is undeniably revolving on a horiontal axis perpendicular to its direction of travel.

I agree.

These last two weeks have probably been hectic for you, but you pulled it off. Good job

Blitzorn

Fri Jun 12 2009, 05:12AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

It has been a bit nutty, but you know what?

I had a BLAST.
This has been one of the cooler and more educational experiences of my life which trust me, although i'm only 17, REALLY means something.

In the immortal words of my favorite cybernetic assassin, "I'll be back."

(insert station wagon coming through wall here)

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