Xray high voltage multiplier

[Dennis P Brown]

If you search the recent work of Nathan Marshall he used a ZVS (avialable online cheaply) to create a high frequency driver for his system. What he did would work for your multiplier very well.

[Sarmad suseyn]

Hi guys and thanks for the help
I managed to make it work by another way
I removed the transformer and i hooked it to neon HF power supply with 12kv .
And it worked perfectly.
For now i can't check how much voltage im getting.
Have to get HV probe for 100% measurement. But
The spark length around 6cm between two electrodes
Check the attached table . It could be around 160kv.

[John Futter]

pop rivets do not equal the balls referenced in your spark length vs voltage table
my guess is somewhere between 50 -60kV but the sharp edges of the rivets might make that even lower 30 -40 kV
yes you are going to have to get or make a probe to check --you are going to need a high voltage probe anyway so now is a good time to source /make one

[Rich Feldman]

That's a great idea, driving voltage multiplier with a high frequency neon sign power supply.

As John said, you are misreading the table you attached.
(Which appears to be cut and pasted from an old paper handbook. With due respect, Jochen Kronjaeger should not have posted it with a copyright symbol and his name.)

Let's see what gaps it says for Upeak = 160 kV.
5.95 cm between 50 cm diameter balls.
5.95 cm between 25 cm diameter balls.
7.37 cm between 10 cm diameter balls.
28.1 cm between needle points.

Now look at the row for 60 kV..
2.01 cm between 25cm diameter balls.
2.02 cm between 10 cm diameter balls.
2.17 cm between 5 cm diameter balls.
2.82 cm between 2.5 cm diameter balls.
6.81 cm between needle points.

The point we are trying to make is really about non points.
Spark gaps in air are a practical way to measure very high voltages, but to use standard reference tables you need "large" spherical electrodes.
Measuring spoons? Cabinet door knobs?

I stand with John in urging you to get or make a proper kilovoltmeter.

Next I would suggest a proper resistive load. Don't worry, that neon power supply will never deliver 360 watts.
The HV resistance of your kilovoltmeter is a good starting point, if designed for (say) 0.1 mA.
Whatever voltage you measure, now add a parallel resistor to draw, say, 1 mA. Voltage will be lower, and you will find out if the NST is still happy.
Voltage multiplier itself is probably designed, conservatively, to handle about 10 mA for a couple of seconds.

[Sarmad suseyn]

Thanks John and Rich
The picture was done without putting it in the oil. There is so many sparks in the circuit see picture. Maybe this?
https://www.extremeelectronics.co.uk/ca ... calculator
May be i can calculate the output voltage. But i cant calculate the multiplier stages.
Or you have an idea about a good way to make a good prope?
Here where i live still full curfew .
Thanks

[Dennis P Brown]

While certinly that is a HV driver x-former - its 12 kV going into a many stage voltage multiplier - the issue is very HV x-formers tend to be very low current output devices and that is the bane of VM. Especially half wave ones.

I previously posted on a site that allows one to calculate the final voltage (search my name as author and voltage multiplier and calculator.) But a rough estimate (not an accurate value) is simply done by counting stages and multiply by a reduced factor like 1.6. So, if you have seven stages you'll get something like (but very rough ball park value) of 130 kV. However, the final voltage tends to fall fast with extra stages; so the fewer the stages required, the better. As such, using a two stage unit will more reliably raise 12 kV to something closer to 40's of kV than trying to build more stages with a lower voltage x-former. So a seven stage unit will get nowhere near the 160 kV you are aiming for. My rough number is very likely too high as well.

A few points: you will get no where near that HV value until the assembly is in oil. (Rule of thumb - 20 kV in air max/stage for any VM stage.) Also, the current output will be very, very low compared to the 30 ma input (the VM calculator will give a fairly accurate current value.) Measuring that very high voltage isn't easy at all. Again, corona will be very serious unless the measuring system is also under oil.

Air arcs simply are not very accurate - as pointed out, geometry of the source electrode is an issue and the values really depend on humidity (the tables are for very dry air which isn't available in spring/summer, generally. Humid air conducts very well allowing low voltages to make longer arcs.) You can't use a support surface as pictured - any surface within a number of centimeters will cause the corona to interact with it and then a 'corona field' follows the surface enabling a far lower voltage to jump a far larger length (well over the real value.) That is, those tables are for free standing/very isolated electrodes only.

Do connect the HV lead from the NST directly to the borad (thinly insulated wires will not only shock you, they allow leakage.) Then place the VM under oil. Synthetic motor oil is excellent to use.

[Rich Feldman]

Traditional accuracy of HV measurement by spark gap is often stated as +/- 3%,
after proper adjustments for electrode geometry and air density and humidity.
It's not easy to do better with a DIY kilovoltmeter, unless you have an accurate HV reference for calibration.

>>Humid air conducts very well allowing low voltages to make longer arcs.

I don't know about Tesla coils, but most literature says the opposite for DC and low frequency measurement by spark.
Might be counterintuitive, but breakdown voltage for a fixed gap goes _up_ with humidity.
The text in this snip discusses some variables not shown in the figure.
https://www.eeeguide.com/sparkover-volt ... here-gaps/

.
Along similar lines, I sent a bug report to some educational site about density of air. The writer did a good job of addressing the ambiguity of "Standard Temperature and Pressure". Then wrongly said that humid air is more dense than dry air.

[Richard Hull]

The board was designed not to arc. The board arcing tells me you are applying way more input volts from the neon than the board input was designed to handle. HF chicom neon systems can't be variac controlled of course. Assuming the board components will take the over volting, oil immersion is the solution coupled with a proper electronic voltmeter system.

Neon lighting can't tell the difference between 60hz and 25khz. Tat multiplier board relies on HF to make it deliver any sort of current with those tiny caps. HV HF crawls over insulators with ease.

In the end, what ever comes out of the supply is what powers you x-ray tube, design rating be damned.

Richard Hull