need alil help

[James]

okay well i have a 15kv neon sign transformer connected to a variac to control input voltage but i dont seem to be getting good enuff dc voltage... i have 2 hv mircowave diodes(one on each hv out) and then they are joined together at the other ends and i have that connected to the inner sphere and the outer casing of my fusor is grounded(i dont have a outter grid because my chamber is sphereical) is my setup correct?

[Richard Hull]

You should be getting about 8 - 9 kvdc with this full wave rectified system. A key question............Is the transformer case screw terminal gounded? It must be to complete the FW rectifier circuit.

The diodes must connect together anode to anode, for negative voltage output. The cathode ends (banded) should each go to each transformer HV knob.

Richard Hull

[James]

okay my setup should be correct then, and yes the transformer case screw terminal is grounded and i have a wire running from that screw to the fusor to ground it, and the hv wire running to the inner grid

[tligon]

Be aware that if the specs on the microwave oven diodes are like those I've seen, single ones will be hanging on by their fingernails running on a 15 kV transformer.

Think safety, then think safety again, then turn it on and see what happens. If you've screwed something up but have a decent setup where you are unlikely to get zapped or start a fire, the worst that is likely to happen is pops, arcs, and fizzles that are exciting, but educational. The transformer will probably take anything you do to it, at least momentarily.

Just be ready to kill power to it if anything goes wrong.

[AllenWallace]

The 8-9 kvdc that Richard Hull mentioned is the NO LOAD voltage.

NST or Neon Sign Transformers are current limited, meaning that their
voltage drops down as load is increased, giving them only a few hundred
volts then connected to a fusor. You will see a nice plasma, but no
neutrons. It is highly recommended that one should use a NST in the first
power supply that an expirementer should build. Everyone should build a
low power-air 'Demo' fusor first and then build a second fusor with high
power/Deuterium.

Invest in a proper High Voltage probe (eBay). Also search the Fusor
forum for the letters NST and you will find a wealth of information.

[Carl Willis]

Just a thought: are you using a real transformer or one of those "electronic transformers"? Suggestions so far have presumed you are using a real NST. The electronic units are switching supplies that are known to be difficult in most any application besides driving neon signs.

-Carl

[Richard Hull]

I have gone over the classic neon tranny over and over again under a plasma load. You WILL not achieve anything like 7-8KV under a plasma load as the transformer will automatically dial itself back drastically with a drastic load.

check out my paper
viewtopic.php?f=19&t=7945#p57349

Richard Hull

[waltsphotos]

Warning this suggestion could be lethal to anyone touching it; for days or weeks after the unit is turned off. Think safety first

One of the "tricks" sometimes used in tesla coil design is to add high voltage capacitors to the circuit in series or parallel. In this case, I think you would want to add a parallel capacitor before the rectifier circuit. This will help the transformer from dropping voltage and current and smooth the input to the rectifier circuit. You should also add a capacitor to the output of the rectifier circuit to smooth the voltage (most text book information on full-wave bridge rectifiers suggest this).

[James]

hmm not a bad idea... altho im thinking of just puting aside the NST and buying a profesional HV power source.. any sugestions?

[MSimon]

I have added a bunch of stuff to the MOT thread.

If you are into electronics a little - I would suggest a pair of MOTs and a full wave Crockoft Walton multiplier.

If you are into electronics a lot regulate the supply. I Have put a preliminary circuit up (MOT boosting thread) and can help with the design.