Parts for HV setup for Demo Fusor

[Vikram Singh]

So i have a NST ( 15000 v and 30 mA0 and a variac and HV wire capable of 15kv wht other parts do i need?
such as the diodes
and the HV?
Why would the specifications be on the HV power Supply?
and the diodes wht kind would i be using?
* i read the FAQ but i still dont understand the HV stuff
I understand everything else about the fusor except for this part of it?

[Tyler Christensen]

If you are asking these questions (what diodes are for, what type, etc) honestly you should probably find a local advisor to help in the high voltage area. These questions after reading the FAQ indicate that you have zero background in electronics or electrical engineering, and are at a high risk of really hurting yourself (as fusors, even demo, are running lethal voltages. While an NST is a somewhat safe high voltage source, you can definitely still injure or kill yourself).

Otherwise you should probably study basic electronics before proceeding. A 15kV setup should not be your first rectification experience.

[Vikram Singh]

i nvr said that i didnt know wht a diode was
wht i asked was whtkind of parts i need
i kno tht with two diodes my power goes down to 7.5kv
furthermore i need the diodes to rectify the nst so it is DC power
for type i know its a microwave oven diode
i posted this question for the type of feedthrough i need and i didnt say i have 0 understanding i just dont have complete

[Tyler Christensen]

I'm a little confused about your feedthrough request, your original post had absolutely nothing to do with feedthroughs.

Anyways, it sounds like you already know what kind of diode you need, enough voltage (your 7.5kV, although do multiply by 1.41 to get the DC peak voltage), and enough current for your desired operation.

[Vikram Singh]

oops my fault!! srry man!! idk wht i was writing!!
I just need help with the feedthrough really i dont understand tht really well and i dont know how it works and how it is supposed to hook up to the inner grid
i dont really understand the purpose of the guard.

[Tyler Christensen]

A feedthrough is an insulator, usually ceramic, with a high voltage terminal, and a metal flange. Keeps the high voltage away from the ground on both the inside and outside. Not much more to it. Figure out a way to electrically connect your grid to the inside. Spot welding, welding, friction fit, there are many ways to do it.

[Vikram Singh]

kk tht makes sense! so how do i ground this?
wht should the specifications be on this feedthrough?
and i was searching for one online and wht should the price range be for a new one?

[Vikram Singh]

This is the diode im getting
http://www.electronix.com/microwave-ove ... -5377.html

[John Futter]

Vikram
Most of us do not speak TXT so please try to use normal english

Ok your wanted diode is 12kV peak PIV.
Normally one would use this to a max of 4kV to ensure it lives a useful life. So now each diode in your rectifier will be made of four diodes in series with high value resistors in parallel with them (say 470K ohm), the resistors are to force PIV balance across the diodes so that they share equally the PI voltage.

[Jeroen Vriesman]

Connect 2 of your "microwave oven diodes" in series to rectify upto 20kV, or 3 for 30kV

You need a very high resistor parallel to the diodes in order to balance the reverse voltage.

e.g. if you would allow 10 microamps of reverse current en 10kV per diode, the resistance would be 1E+9 ohm.

You can make these kind of resistors with e.g. 20 x 47 Mohm series (per diode), which is saver than just one resistor.

remember your max reverse voltage is the DC output voltage ( sqrt(2) * [ac output voltage of transformer ) times 2.
When rectifying with one diode (or one series chain of diodes) during the negative cycle of the transformer output, the voltage across the diode is the +HV dc voltage, plus the abs. value of the maximum negative peak on the transformer output.

So that's 2 * sqrt(2) * (ac voltage on transformer output)

[John Futter]

Vikram /Jeroen
Sorry I made a blue the other night
I still use a sliderule (batteries never go flat) you have to keep track of the powers of ten in your head.
My suggested values should have been 47M ohm, one per diode VR68 series from BC components these are rated @ 9kV and are very cheap.
Because of the negative resistance of plasma potentials and the possible use of an output smoothing cap I was working with 20 x the 10uA reverse leakage to make sure that when the diodes get hot the balancing current would still be enough with greatly increased leakage.
secondly assuming a network of u-wave oven capacitors on the output this set of PIV protection resistors would discharge the voltage on the capcitor/s to a safe value within a couple of minutes (5xRC= 98% reduction in voltage)