Xray high voltage multiplier

[Sarmad suseyn]

Hi
With luck got my hands on xray tube with multiplier circuit.
I think its around 70 to 80 kv. Which is perfect for my fuser reactor.
My only concern is the transformer have three inputs.
I got a circuit diagram showing AC input with two wires
I have there in the board. Where to connect the AC .
Thanks

[John Futter]

Sarmad
I think you will find that you have high frequency unit there
Designed to be driven at 30 -70 kHz
the three wires are likely to be for half bridge drive

[Sarmad suseyn]

Hi john
So should I be using number 1 an 3 wires?
For the AC voltage . We are using 250v 50 Hertz where i live
Is this correct?
Thanks

[Sarmad suseyn]

More detailed picture

[Rich Feldman]

I stand with John, in betting that you need a high frequency inverter between wall plug power and that transformer.

Suppose you want to give it a try with 50 Hz.

Step 1: measure the resistance between the three input terminals. That may prove or disprove that it's a center-tapped primary winding.

Step 2: Figure out how to apply 50 Hz limited to a few volts and a few amperes, whichever comes first. I bet it will be a few amperes, with less than 1 volt across the primary. Measure voltage at secondary terminals and multiplier output, and report the results here.

[John Futter]

Sarmad
All the clues are there
now calculate how much current you will have at the output if you use 50 or 60 Hz 220 volts
clue =capacitor value of 1000pf


for 50 /60 hz work I would expect 1,000,000pf or more per capacitor

you can try putting in your component values in to here
http://www.blazelabs.com/cw-brm-java.asp

[Dennis P Brown]

I'd suggest you disconnect that x-ray tube before applying power; best to be safe than get a dangerous exposure. Also, be careful - caps charged to HV can deliver a dangerous shock. Small caps like that simply won't provide anywhere enough power to drive a fusor at 50 Hz. John is guiding you to this through "How to calculate" app.

[Sarmad suseyn]

Hi all
Some people like to learn from there mistakes. Like me
Just went and connected it to 220v . But before that i added 2 fuses with 13 amps one on the circuit and one in the socket.
First time when powdered on had a boooof
Ok so i changed the fuse, and i thought because no transformer oil !
So i covered it in oil and had another boooof
The circuit still alive which is good.
By the circuit diagram it shows Ac voltage . Buy i think 220v
Is too much for it. Maybe it needs 110v?

Thanks for the help

[Dennis P Brown]

Hello and learning by doing is ok for circuits and voltages that aren't lethal; unlike fusors. Can't say if yours is in that class but the last way one wants to prove that is via getting hit.

As such, I'd suggest (as others here have) apply a very low voltage - i.e. use a variac to control input voltage - if that x-former does use 110v AC (50/60 Hz), and you apply that voltage, the output will reach the rated value (possibly 70 kV.) Voltages above 25 kV do not behave in a fashion that one can easily expect; I developed a 100 KV voltage multiplier supply and I abandoned it after one use for that very reason. Far too dangerous and unstable to operate - that is, even under oil, the output was trying to reach ground.

Also, unless you have a very special HV meter (mine only goes to 50 - 55 kV) you need a low voltage input to that device so the average voltmeter (500 to 1000v) can read its output.

Blindly applying full voltage to an unknown voltage multiplier/transformer system isn't smart nor necessarily safe.

[Rich Feldman]

Apparently the transformer-multiplier is not very precious to you.

110 V will surely give you another boooof result, maybe with one less o than 220 V. Why did you pick 13 A fuses, do you think the transformer primary can withstand any current-time combination that doesn't blow the fuse?

As mentioned before: if you insist on applying 50 Hz AC, and don't want to blow anything up, you need to limit the current. As with a ballast: incandescent lamp in series. I bet you will measure 219 V across the lamp and 1 V across the transformer primary.

Here is another view. The primary voltage which a transformer can handle, without core saturation, can be stated in volts per hertz. From the pictures, I will wildly guess that yours is good for 10 mV per hertz.
That means you can drive it with 220 V at 22 kHz, or 0.5 V at 50 Hz, plus some extra voltage to cover the I * R drop from resistance of the primary winding. You never told us what that resistance value is.

If the transformer were designed for 50 Hz, its core would be made of laminated steel instead of ferrite.

Nuclear physics experiments at home don't always require knowledge of electricity.
But fusors need more than some newcomers (and precocious high schoolers) want to bother with.

[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