40000V transformer help

[Souper man]

I am having trouble finding a transformer capable of getting up to 40000V. It must have a input of around 20V and a output of 40kV. It is for a Marx Generator. After some revisions, i need a much higher voltage than 1000V as orginally thought. Must be DC. Milliamp rating of around 2mA. Ferrite core based. Preferably an easy to use type.

 

[Papabravo]

So back of the envelope you could have let's say a ten turn primary winding and 20,000 turn secondary winding. The DC resistance of 20,000 turns of say 26 ga. wire would probably cook the thing. Like air travel in some parts of the United States -- I don't think you can get there from here.

 

[TheVictim]

The problem with transformer secondaries stepping up to that much voltage is the dielectric strength of the insulation in your windings would break down long before that. You would need very thick insulation, and stepping up that high you would also need a lot of windings. This would make the secondary very large compared to a small primary, requiring a HUGE and very HEAVY core.

 

[HarveyH42]

Didn't ignition coils in cars produce 25-50 kV? Not too sure about the modernized ignitions (fortunately no problems to fix, so far). There were circuits for Tesla Coils, fence chargers, jacobs ladder, ion generators using them.

 

[Hero999]

I've tried building high voltage flybacks before and failed.

The problem is insulation. I would recommend putting a layer of insulation between each layer of turns and use several thin (disc shaped) secondaries in series.

 

[Oznog]

Looking up a Marx Generator, looks like you need DC, not AC. This will require you to rectify your output voltage but at 40,000V that will be tough. I don't know of any diodes or transistors which can do it.

Starting from a lower voltage and putting it through a whole lot of stages of voltage multiplier may be more practical.

 

[Papabravo]

Didn't ignition coils in cars produce 25-50 kV? Not too sure about the modernized ignitions (fortunately no problems to fix, so far). There were circuits for Tesla Coils, fence chargers, jacobs ladder, ion generators using them.

Possibly, but a coil and a transformer are two different animals. The flyback pulse on an ignition coil is high voltage, but very short duration.

 

[justDIY]

how does an x-ray power supply work? don't they generate similar voltages?

what about this 60kv unit:
**broken link removed**

 

[chemelec]

40,000 Volts may be a problem to obtain directly from a transformer.

But you can use a Lower voltage and than a Cockcroft-Walton Multiplier circuit to raise it up to the voltage you want.

I Have the Diodes and Capacitors that can do that high of voltages.

 

[Sceadwian]

Yeah, Xray supplies are in the 40kv range.

 

[chemelec]

The X-Ray Transformer I had was rated at 220 VAC in at 100 Amps Maximum and 125 KV out. Not sure on that Amperage, But it put out QUITE THE BIG SPARK.

It weighed about 200 pounds, about 20 Inches in diameter, about 36 inches tall and was Oil Filled.

40KV Sounds Quite Low for an X-Ray unit.

 

[pfofit]

how does an x-ray power supply work? don't they generate similar voltages?
what about this 60kv unit:
**broken link removed** for powering a wide

From the website:
variety of high energy & fascinating experiments such as homemade X-ray tubes
Totally irresponsible. Nice way to kill/mutate yourself, ever hear of marie currie.

Top Xray supplies can pump out up to 150KV, dental units up to 70 KV
Old mamo units ran at around 40 KV (self rectifying tube), the newer mammos, when i left a few years ago, up to 70KV.

Average xray supply would max at 150 KV @ 60 -70 KW the biggies were 125KW

The big ones were 380-440 three phase input with a dual secondary windings of 75 kv each applied across the x-ray tube. (A fancy diode with a motor in it.)

The motor is to rotate the anode to dissipate the heat. 99% of energy applied to tube is lost to heat.
The cables from tank to tube were 3/4 inch thick with three 18 guage wires in the center.

The transfo's with big heavy and immersed in high voltage tanks full of oil along with diode sticks, bleeder networks, Filament tranfos and switching mechanism. ( most xray rooms contain two tubes that are supplied by one tank.)

The smaller units such as dental and mammography have combination tube, transfos and rectifiers mounted in a sealed oil filled unit called a tubehead. This eliminates the special Hv cables.

The later units reduced the tranfo size and cost by going high frequency.
Instead of 50-60hz, 30K to 50kHz. This provided little ripple, which was desirable as applied tube voltage represented the xray penetration "quality"..

The tanks, oil etc are still neccessary, although the weight of the tanks went to a couple hundred pounds down from several hundreds of pounds.

However these would be overkill, dangerous and toxic for your use..

We also had IA (image amplifier) tubes somewhat similar to an picture tube working in reverse. They used special sealed tranfo and were jack up to 30KV plus by a cascade of voltage doublers in sealed black blocks.

This may be more to what you may need.

cheers

 

[justDIY]

From the website:
variety of high energy & fascinating experiments such as homemade X-ray tubes
Totally irresponsible. Nice way to kill/mutate yourself, ever hear of marie currie.

I think there's just a few differences between refining and concentrating uranium and radium salts, in a home kitchen (as did Curie), and playing around with low energy xray radiation (as did Rontgen.)

But I don't think that either Nuclear or Electromagnetic radiation is the goal of the original poster, I think they're just after big sparks?

 

[pfofit]

I think there's just a few differences between refining and concentrating uranium and radium salts, in a home kitchen (as did Curie), and playing around with low energy xray radiation (as did Rontgen.)

There is a difference and it is the time it will take you to die.
BTW, Roentgen died from intestinal cancer way back in the early 20's. The theory with any radiation is "less is best". It only takes one photon to mutate the DNA stucture in a cell. That is just one high speed electron being decelerated at an anode. The higher the voltage applied the higher the penetration ability of the photon. Some wavelenghths of X-rays overlap gamma rays on the EM chart, however, the difference between xrays and gamma rays depends on the method of production, X-ray photons are generated by high speed electron interaction and gamma rays by nuclear decay of atomic nuclei. Same wavelength same energy.

Weather the radiation is man made or a naturally occurring source is immaterial when you get diagnosed with a fatal disease. Unlike "sources" which are "always on", x-ray machines emit only while the button is pressed or it has a defect.

They do not go to all that radiation protection circuits and radiation shielding in any kind of tube working in excess of 20 kv just because they can. The x-ray tech does not run and hide behide lead covered walls and lead glass for exercise. Doctors, x-ray techs and service engineers like myself do not wear bulky awkward lead aprons as a fashion statement. Note, lead aprons are only effective on scatter, not the direct beam and provide little protection after 80kv or so. They also do not protect the head or eyes and many don't protect the thyroid gland.

But I don't think that either Nuclear or Electromagnetic radiation is the goal of the original poster

Neither do I, My point was to let peoples be aware of the potential danger. People get hold of and take home dangerous stuff all the time to play with. Unaware of the pitfalls. A discarded/unwanted dental unit can easy be picked up and dropped into the back seat of your car. Perhaps it's toast, perhaps it was just old or perhaps is was not shutting off. Lay that defective unit on your bench and plug in for awhile and i guarantee you will regret it it. Someday.

Chemelec, take care with that tranfo. Although fun to experiment with, those old xray tanks, depending on the manufacturer may contain high levels of PCB's. They tend to get oil film all over them and some type of glove would be in oder

cheers.

 

[CheapSlider]

You haven't said what the marx generator is for.
The output from a car ignition coil will be DC pulses in 10s of kV. It should be possible to get a suitable coil from a car breakers or car scrap yard fairly cheaply - you could get a few coils to try.
Diagram

The circuits are simple. The hard part is getting suitable HV components. Not the sort of thing your local shop will have in stock. Most common parts have very limited voltage ratings.

 

[HarveyH42]

I frequent several gadget sites. Last time did a search out of curiosity...

https://www.electricstuff.co.uk/marxgen.htm

Seems like a pretty simple and thorough project to start you off. I think I saw the Ion generators at electronic goldmine...

 

[ronsimpson]

The original post asked for 40kv at 2mA. That is about right for a large color TV flyback transformer. The output is DC and will have a load resistor to bleed off the voltage after the power has been turned off. It is important for the voltage to go away after the power is off. There is some current limiting. When I build this type of supply I measure the current at the cold end of the high voltage winding. Shut down if the current is too high. Your life may depend on it. The government made us add current limit. The diodes, resistors and capacitors are inside the transformer. The capacitor may be too small. Normally the CRT adds more capacitance. It is a mildly safe and easy supply. A medium size TV might get you 30 to 35kV and if designed correctly will let you go before death. Your pants may be wet. See the last picture in the link on the post before this one. https://www.electricstuff.co.uk/marxgen.htm

Camera flash transformer only output micro amps. Good for sparks but no 2mA.

Auto coil needs diodes and capacitor. I do not know how much power you can get. I think it is not very much. I have 40kv diodes. You can string together 40 x 1kv diodes. I would place a 10M resistor across each diode. All diodes must be the same kind and should be of the same date code. The layout must be like the pictures in the link.

I used a neon sign transformer for a lazar project years ago. 12kv at 200 watts.

Radio transmitter transformers: My last transmitter had a 6kV 4A supply. Too heavy to carry and deadly.

X-Ray transformers are very dangerous! I do not have any now. They will kill you. There is a saying that if you keep one hand in your pocket you cannot get hurt with electricity. At 40kv you will get hurt. The X-Ray transformer will kill you with both hands in your pocket. There is no current limit!

If you are just playing around have fun. If you are going into production email me. There are tricks. I have seen factories that thought they know high voltage, have to replace in warranty, 10,000 unites in a year.

Keep safe.