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Modifying output of an NST

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Plasmana

Sat Aug 28 2010, 03:33PM

Registered Member #3108 Joined: Thu Aug 12 2010, 05:37PM
Location: Worthing, England
Posts: 72

HM_Murdock wrote ...

ok, that makes sense...

So if I have it right, I need to be able to make high volts (upwards of 60kV) and low amps (1 or 2 mA) to get what I am looking for...

Sounds like a FBT driven TC?

Or, is there some way to step up the volts and reduce the amps of the NST?

You can achieve large arcs using just the flyback transformer. Yesterday, I managed to pull out some deathly long white arcs (10+ cm!!) from a small flyback powered by the mains..

Increasing the input voltage for the NST? I don't think it has been done yet, it would be interesting to see what would happen! You could buy a large step up transformer (120VAC to 240VAC), although they are costly...

HM_Murdock

Sat Aug 28 2010, 03:58PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

I was more thinking of some sort of circuit that could take the 15kV 30mA coming from the NST and turn it into much higher voltage and lower amps...

Not that I know of such a thing, or that it is even possible (or feasible) to do so...my lack of theoretical knowledge is showing.

From what (very little) I know, the concept I have in mind would be something like running the output of the NST through something to burn off the amps (heatsink mounted bank of resistors, series of lightbulbs?), then running the lower amp (and by then I would assume slightly lower voltage) output from that into some sort of transformer to step up the remaining voltage while leaving the amps low?

Plasmana

Sat Aug 28 2010, 04:28PM

Registered Member #3108 Joined: Thu Aug 12 2010, 05:37PM
Location: Worthing, England
Posts: 72

HM_Murdock wrote ...

I was more thinking of some sort of circuit that could take the 15kV 30mA coming from the NST and turn it into much higher voltage and lower amps...

Just about every new HV enthusiast think that could be possible, even I did and tried it out when I started doing HV.

The answer is simply no, it won't work. You will more likely to destroy the insulation on the primary winding. Even it does work, the secondary winding insulation will probably not hold up for long.

I don't know but can the HV outputs from the NST's be connected in series without the insulation burning out?

Adam Munich

Sat Aug 28 2010, 04:30PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

This will up your voltage. You'd only need one stage to get it to 30kV.

It may be possible to smooth the output with some caps in series, though I'm not sure if anyone has ever even tried that.

And no, NST's can't be put in series. They'll burn out.

Proud Mary

Sat Aug 28 2010, 05:10PM

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

There is no theoretical reason why you cannot multiply the output of your NST using standard rectifier and capacitor circuits, but whether it would be practical or not would depend on your access to components of suitable values and ratings.

I understand that by "15kV NST" you intend what I would call a 7.5kV centre-tapped transformer (i.e. 7.5kV-0-7.5kV) It would not be good practice to leave the centre tap floating in such a transformer, which will not have been designed for a 15kV withstanding voltage.

There is nothing to stop you constructing a full-wave voltage tripler, or even quadrupler, using your transformer, though the voltage will sag badly when any current is drawn unless you are able to obtain large capacitors with suitably high voltage rating.

The lower the frequency, the bigger the capacitance values in a voltage multiplier must be, which is why it is not usually considered to be practical or economical to multiply alternating voltages at 50 or 60 Hz. However, where only very small currents are required, there is still a place for voltage multiplication at 50Hz. For example, I use very small 240-240 PCB isolating transformers to obtain 600VDC to supply Geiger-Muller tubes, which need less than 100uA on avarage. 50Hz voltage multipliers using electrolytic capacitors are sometimes used in thermionic valve power supplies needing 600V at a few hundred milliamps.

As always in engineering, you must first define the needs of the application - in this case, what voltage and current are required - and build the power supply accordingly.

811a vttc

Mon Aug 30 2010, 01:50AM

Registered Member #3097 Joined: Tue Aug 10 2010, 03:35PM
Location: Ontario Canada
Posts: 13

Plasmana
"You could buy a large step up transformer (120VAC to 240VAC)"

Go to Walmart, and buy plug adapter for Europe, It converts 230 vac to 115, take it apart and hook it up in reverse, this cost about $20

HM_Murdock

Mon Aug 30 2010, 02:09AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Thank you all for the answers and advice!

Since it seems I am trying to make the output of an NST behave like a small TC, I am just going to concentrate on designing a small TC...

seems logical at this juncture.

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