I am trying to create an arc generator and I have read about the marx generator but I am looking into more compact modules like the image below. All the ones I have found seem to be fake and actually supply less than 1/10th of what they are advertising.
Is it really possible to “boost” 6 V DC to above 50kV? Or even 400kV?
Of course. One common example of something similar (although not as extreme as your specs) is using 12 V in a car to make several 10s of kV to fire the spark plugs.
The same concept can be scaled up to make higher output voltages. It won't be easy to build something with that stepup ratio and output voltage yourself, but the physics is certainly possible.
A battery powering a dc motor in a Van der Graaff generator can produce a million volts quite easily: -
- Take your 6 volts and run it through DC-DC boost converter and then an inverter, you now have really rubbish AC at a slightly more respectable voltage.
- Feed rubbish AC in to a solid state boost circuit, say a Cockroft-Walton voltage multiplier
- Feed the high voltage through a current limiting resistor if you want any kind of continuous draw. Don't bother if you just want a spark.
- Do not lick the operational terminals.
The trick lies in how you manage to shove so many stages of a CW in a reasonably compact space. You're slightly saved on the issue of voltage isolation since the output terminals are at opposite sides of the ladder.
Can you get 800kV out of this? I highly doubt it. Let's say you get a boost converter to add an order of magnitude to your input voltage and the CW gets 60V... each stage of the ladder adds the input voltage to the output, so 10 stages is still only 600V output. As you increase your input voltage you also increase the boost per stage at the expense of needing all your components being able to handle the increased voltage.
I would imagine that with appropriately rated components (and a lot of them) you could step 6V to 800kV with this kind of approach but your output duty cycle would be ridiculous and the thing would be rather big. A lot of work for one spark. You'd probably also need a flyback to get the input to a level where the CW is practical, and at that point you're best off just getting wall AC and using a transformer to drive a CW or Marx up to that voltage.
As for that thing in the picture... some capacitor stack maybe? Weirdly wound transformer? Leiden jar?
Yes, quite easily. The 1990s had hand-held TVs that actually had Cathode-Ray Tubes like "proper" living room TVs; those were powered using a couple AA batteries (ie. 6V or the like).
CRTs need a couple of kV to accelerate electrons towards the screen. So, building a device that does only that is actually not that hard – these TVs were (presumably) simply based on commodity flyback transformers.
Here's a video showing the use of hand-held Electrostatic Discharge generators; these are available in battery-operated versions.
Now, from 10–25 kV it's still quite a way to 0.8 MV, but the transformer principle used in such devices does allow for higher voltages, too. See Tesla Coils for a classical way of building such high voltage generators.
EDIT: If I'm already promoting that guy above, here's a tesla coil driver circuit from his website:
Circuit is omitting the flyback diodes integrated in the MOSFETs.
As you can see, it's operating from 12 V - but there's no particular reason this couldn't work with 6V from a battery, either (though you might need to use different transistors); the 12 V might also be generated by a separate step-up converter from any lower voltage source. V_SUP is typically higher - that's where you'd use a step-up converter to convert e.g. 6 V to 32 V first, in order to be able to drive the coil with high power. Roughly guessing from the spark's length, this is around 100 kV.
I'd recommend that you buy Prutchis' book: "Exploring Quantum Physics through Hands-on Projects" and then go to their web links:
- d.i.y. 250 kV High Voltage DC Power Supply with Neat Trick for Switching Polarity
- d.i.y. 15 kV @ 30 mA Floating-Output AC or DC High-Voltage Power Supply
- Original Source for Flyback Driver Hack?
- Adding Your Own Primary to High-Voltage Flyback Transformer for Resonant Driving
- diy Low-Cost, Regulated, Variable, Low-Ripple High-Voltage (2kV) Photomultiplier Tube Power Supply
- Assembly View of diy Variable-Output, High-Performance PMT High-Voltage Power Supply
The book is worth it. I picked it up for less than $59 new, back when it wasn't so well known or the value of the US dollar was different. Amazon wants more, now. But you can search around and see what you can find. The book is definitely worth getting, though. Very good stuff reading through it.
And you will be able to then make up some defensible reasons for wanting something like this.
From my high-voltage class I remember that the maximum field strength is about 30 kV per centimeter. And this is for a homogenous electrical field, e.g. between large spherical conductors, where the conductor diameter is large compared to the gap distance.
Hence, for 800 kV you need an air gap of at least 25 cm, between spherical conductors with a radius of, say, over 1 meter. Just google at "high voltage lab" and you will see such spheres. The Vandergraaf Generator, sketched in another answer, has such a sphere, and its diameter and distance to Earth limits its top voltage.
Looking at your picture with thin wires expecting to carry 800 kV, I do not see a homogeneous field, and the distance between the conductors is in the range of millimeters. If you charge up those wires, you will get sparking long before you reach 30 kV. Not only sparking at the end of the conductors, through air, but also through the plastic insulation.
For illustrations about the difference between conductor shapes, search for Rogowski Profile or Electrode, e.g. here
So the question is not how to transform a low voltage to a high voltage, but how to prevent sparking.
Andy's Van de Graaff generator definitely works. Tesla coils do as well. Google search homemade/designing Van de Graaff generators/Tesla coils. I'm not familiar enough with Van de Graaffs to speak on how easy or cost effective they are to make but Tesla coils definitely seem doable for someone with the time and desire to learn.
The only part you probably wouldn't want to make yourself is the initial step up transformer. That's a lot of windings to hand wind. Used microwaves go for 10-20 USD at thrift stores here. They're usually around 1500W and 2kV.
This was one of the first detailed description of building a large one that I came across: http://www.rmcybernetics.com/projects/DIY_Devices/tesla-coil-srsg.htm
He used a neon sign transformer. It is a higher voltage lower current transformer. It's probably possible to compensate for that in the design of the resonant transformer that it feeds. Otherwise you could get transformers with close current ratings and put the secondaries in series. I don't know where to reliably find neon sign transformers for cheap. I have only found one and it was by luck. It was 10kV like his but rated for 10% of the current.
How do all the stun gun brands advertise bizarre voltages like 1MV?
The stun guns and tasers that advertise 1MV may be able to reach 1MV. I believe they only reach the advertised voltage during open circuit conditions. Once you break down an insulator it becomes easier to keep current flowing than it was before you did. Due to internal resistance a voltage source's output voltage decreases under load. So when the terminals on a stun gun or taser arc through air or flesh the voltage drops due to the flow of current. Look up Jacob's ladder traveling arc to see a demonstration.
The principle on which the most common type device to do this works is identical to the way in which a hammer can drive in a nail or break a hard object: force is proportional to the rate of change of momentum. The hammer's momentum is built up by applying a modest force during the second or so that the swing lasts. When the hammer hits the nail its momentum is absorbed within around a millisecond, so the force applied to the nail is in the region of a thousand times the force used to swing the hammer.
The electrical analogue of force is voltage, of velocity, current, and of mass a quantity called inductance, in which energy is stored in the magnetic field that is generated by any electric current. This energy is analogous to the kinetic energy of the hammer.
Winding wire into a coil increases the inductance and giving the coil a ferromagnetic core increases it more. When a low voltage is applied across the coil the current will build up gradually, typically over tens of milliseconds, until it is limited by the resistance of the wire. If the circuit is now broken the current drops to zero in a very short time, producing a voltage proportional to the current just before the break divided by the time taken for it to drop to zero. If you could stop the current instantly then, theoretically, the voltage produced would be infinite.
This is exactly the way that conventional coil and contact breaker ignition systems work, as well as demonstration devices that used to be common in school physics labs which could generate sparks several centimetres long.
The same principle is used in the "boost" DC to DC converters that generate the 18V needed by by laptop computers from the 12V from a car battery.
Cockroft-Walton Circuits , also known as Voltage Multiplier Circuits , are conventionally used to step up 100 V AC or 230 V AC supply input to EHV /UHV DC , upto 20 MV DC , ac DC supply outputs for Particle Accelerators in High Energy Physics , also as inputs to Impulse Generators for testing HV/ EHV insulators used in HV AC/ DC Transmission lines.
The description of these circuits can be found in WIKIPEDIA or through GOOGLE SEARCH for Cockroft- Walton circuits.
If the input is 6V DC ,this has to be converted to AC by an Inverter or Oscillator Circuit and then amplified to 110 V or 230 V by a step up Transformer . Using a TESLA COIL to further step up this Voltage to Higher Voltages , for input to the Voltage Multiplier Circuit , is also a possible Alternative .
Designing a HARDWARE for this is a VERY RISKY job . So you must take the help of High Voltage Experts from a Technical University.