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My first spark

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Patrick

Wed Dec 05 2012, 07:34AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...

yep 30ma ene245-15030 daehan, plan on use it for this, should be fun :)

based on what i said before, i think youll want to build a simple DC voltage divider Andy, it may take fewer stages than you think. (diode or spark gap switched) as cocroft walton found out in the first nuclear experiments!!!

my previous work here:

might be useful, Andy.

my previous posts indicate 13.06 kV unloaded(for a 12kV RMS),, but ive seen unloaded NST's go much high than there name plate suggests. i dont know if it matters for your purposes but NSTs arnt perfect sine waves either... just FYi

dex

Wed Dec 05 2012, 08:32AM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
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unloaded pig poles output voltages are usually 5-10% higher than rated voltages too.for nsts i don't know the voltage increases under unloaded conditions,but it is not impossible they could go even higher .i guess it is not just internal capacity effect.it is surprising to learn the difference in the case of nst can be quite substantional.only potential transformers are designed for a very preceise primary to secondary ratios under small loads.

Proud Mary

Wed Dec 05 2012, 11:08AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Proud Mary wrote ...

Steve Conner wrote ...

Peak or RMS?

Just for you, Steve, I will re-measure the unloaded secondary output with an electrostatic RMS voltmeter this evening, and report back accordingly.

And the unloaded secondary output result for the Tunewell 5 kV - 0 - 5 kV 30 mA NST is (unsurprisingly) 10.6 kV RMS after 60 secs stabilisation. Equipment used: Meter Unit Type 100 RMS Electrostatic Voltmeter. So the unloaded Vpk will be very close to 15 kV, but I have no way of directly measuring it without at least loading it a little. (I have assumed here that the unloaded output is a sine wave.)

dex

Wed Dec 05 2012, 12:23PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
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something interesting i just found :

kid in this vid claims it is 6 kV nst...but air gap between wires ,where climbing arc starts, looks too wide for me for that voltage.is this the evidence of inital transient in the moment of switching nst on and breaking successive arc that make peak voltage much higher.is this dangerous for nst?

Ash Small

Wed Dec 05 2012, 02:23PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Hang on, I've just remembered something about NST's. My above post isn't entirely correct.

The plate on an NST, say it says 10kV, 30mA, means it can supply 10kV (open circuit voltage) OR 30mA, but not both at the same time.

They are plated this way because you need a higher voltage to initiate the plasma, but you then want a higher current at a lower voltage to maintain it.

There is a 'rule of thumb' method of working out the loaded voltage, but I forget it, For an NST plated at 10kV it's around 6kV, I think.

Proud Mary

Wed Dec 05 2012, 03:35PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ash Small wrote ...

Hang on, I've just remembered something about NST's. My above post isn't entirely correct.

The plate on an NST, say it says 10kV, 30mA, means it can supply 10kV (open circuit voltage) OR 30mA, but not both at the same time.

They are plated this way because you need a higher voltage to initiate the plasma, but you then want a higher current at a lower voltage to maintain it.

There is a 'rule of thumb' method of working out the loaded voltage, but I forget it, For an NST plated at 10kV it's around 6kV, I think.

Yes, Mr Ash, NSTs have magnetic shunts in them, so they perform as current limited transformers.

Patrick

Thu Dec 06 2012, 08:12AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Proud Mary wrote ...

Yes, Mr Ash, NSTs have magnetic shunts in them, so they perform as current limited transformers.

At the risk of exposing my own ignorance, is there a point when the drop of kV and drop of mA become concacve up when graphed as seperate functions? At that point, is the maximum transformers output in VA or Watts reached?

PS, keep in mind im drunk at the moment...

dex

Thu Dec 06 2012, 11:01AM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

max output in VA occurs in the resonant case: Xc=Xm ,i.e. when capacitive load impedance matches magnetic shunt impedance.unfortunately, such situations destroy normally powered nsts

Uspring

Thu Dec 06 2012, 12:16PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

Patrick wrote:

At the risk of exposing my own ignorance, is there a point when the drop of kV and drop of mA become concacve up when graphed as seperate functions? At that point, is the maximum transformers output in VA or Watts reached?

I believe, a shunted NST is electrically equivalent to a perfect transformer with coupling less than 1. Please correct me if I'm wrong.
A transformer with coupling less than 1 looks on the secondary side like a AC power source with a series inductance. That in effect limits the output current and also leads to resonances, if the NST is loaded capacitively. In the case of a purely resistive load max power is reached when the output voltage has dropped to sqrt(1/2) of the unloaded value.

dex

Thu Dec 06 2012, 12:36PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
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Posts: 147

Uspring wrote ...

In the case of a purely resistive load max power is reached when the output voltage has dropped to sqrt(1/2) of the unloaded value.

yes , this is the case where Xm=R.
anybody ,except me,wondering now what is going on with power transfers in some real practical situation where we have nonlinear resistive loads (such like gas filled tubes and neon signs)?

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