Instructables
Picture of Build a simple Marx Generator
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Do you like the idea of tesla coils and other high voltage sparking stuff, but don't have the time, money or patience to build something that is elaborate?

Well, here's a fun 'n' simple project that can make big, fat, noisy sparks at least 2 inches long, and can be built very quickly and cheaply. It might be even more fun to use a marx generator than using a 'very complicated to build' tesla coil!

And to let you know, this "Quick & Dirty" Marx generator website helped me a lot to build this marx generator.

If you have no idea what is a marx generator, you might be saying this in your mind "What the hell is a marx generator!", read about it here on Wikipedia.

WARNING! This project generates very high pulse discharge voltages, which can seriously harm and could be potentially lethal to you and others that are careless to touch the output of the marx generator.


 
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Step 1: So, how does it work?

The Marx generator consists of an array of resistors, capacitors and spark gaps arranged as follows in the schematic...

The capacitors are charged up in parallel through the resistors, so they each become charged to the input voltage. When all of the spark gaps fires (sparks), the capacitors get effectively connected in series, therefor multiplying the input voltage by the number of capacitors and causing a long spark at the end of the marx generator.

Rb has a ballasting effect, it is used to prevent a continuous arc forming across the first gap - this prevents further firing of the marx generator. The value of the resistor will mainly depend on the type of power supply is used, in this case, we are going to use an 10M resistor for this marx generator on this instructable. However, you can reduce the Bb's value to try get more 'bangs per second' without causing an arc forming on the spark gap...


Now, you know how it works (I hope), so lets build it!
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sarvesh74 months ago

can we use electrolytic caps??

you can, but you will need some diodes as well to prevent them form discharging into the power supply. I believe this is called a cockroft and watson cascade but please don't quote me
todybog1 month ago

Is it possible to use a flyback driver (with a lower mosfet, say 60 v) to power the main one, because i have 3 flyback transformers an 0 capacitor banks for the power supply.

maboy3 months ago

if the values of the capacitor (pf, voltage) are changed, would you also need different resistors? I can't seem to find 1000pf 4Kv capacitors, and 6kv caps seem much more common, so could I use those instead without changing the resistors?

maboy3 months ago

Hello. I plan on building your design, all the links are good except for the caps, which seem to have been discontinued. I found a few alternative capacitors so that's not too much of an issue. If I plan on using your power supply design and everything too, can I scale up the generator simply by adding more stages? Or would I also have to adjust the other component values? and how much would adding additional stages impact the spark length?

Ploopy3 months ago

Cool!

endolith4 years ago

Can this really harm you? The idea that a special number of voltage or amperage will automatically kill you is not accurate.

Scuffing your feet across a carpet and touching something metal also produces thousands of volts and large currents, but it obviously doesn't harm you, because the capacitance is small and the spark is very short-lived. Yes, it's high voltage and high current, but the duration is less than a microsecond.

I'm sure it hurts, but I'm skeptical that it would actually cause any harm. How long are the sparks in cm?

10x 1 nF capacitors charged to 7 kV store a total of 250 mJ. Scuffing your feet across the floor stores maybe 60 mJ max by comparison.

"The effects of electrical current passing through the human body are covered at length in the International Electro Technical Commission document IEC 479-2:1987. In this document it indicates that a transient or capacitive discharge, as is the case with static electricity, requires energy in excess of 5 Joules (5000mJ) to produce a direct serious risk to health."
Plasmana (author)  endolith4 years ago
Okay, you made a very good point, can my marx generator kill? Very good question, personally, I will NOT touch it even if its safe. I never really understand Joules as they are many other units of energy related to it. Each capacitor (1nF) holds approximately 4kV to 5kV, how do I convert that to joules to see if its safe(ish) or not?

the formula for joules is volts squared times capacitance

no, it's 1/2⋅C⋅V²

I already did that for you, but I was using 7 kV. :) The energy stored in a capacitor is given by 1/2 * C * V^2, so:

1/2 * 1 nF * (5 kV)^2 = 0.0125 J = 12.5 mJ

Wolfram Alpha can do a lot of work for you:

capacitor stored energy 5 kV 1 nF

Multiply by 10 and you have 125 mJ total, which is 1/40th of the energy that document says is the minimum that will hurt you.

I'm not claiming that this thing definitively can't hurt you. I'm just skeptical that it's dangerous. Even if it's not harmful to health, the shock might still hurt like hell. :D
Its not all about just the Amp or voltage its how it travels through your body if it goes in through your hand and out your elbow (just saying this way you'll see why in a min) all it will do is is give you some bad burns no matter how high either the Amp or Voltage is but if the same current goes in one hand up your arm across your chest and down your other arm it will travel through your heart which will stop it resulting in death. It also doesn't have to affect your heart to kill you it can go through your diafram(sorry cant spell) and your lungs stop working which will cause you to suffocate, if your an electrical engineer you should have learned that in first year I know in my first year we weren't allowed to touch any of the equipment until we did a report on the dangers of electricity and the rick of burns in the lab to show that we didn't just know about the dangers but fully understood them.
For another example, I'm looking at a safety test certification document for EN 60065, and they limit the maximum energy of a discharge to 350 mJ.
The total voltage could be 70 kV, which means the arcs should be able to jump about 1 inch. Does that seem right?

who says this procedure u jus mentioned (Scuffing your feet across a carpet

and ...) produces high currents???
currents than around mA value will shock u and more than 50 mA will kill u jus before u feel it !!!

and the tolerated amperage of ur body during the time is obtained from some equations expressed like the form: (i^2 * t) = cte (around 0.156 i think) so this fact that u mentioned doesn't hurt u cuz the values are lower than this equation. and ti is not related to the capacitance. there is a kind of a surge formation when u touch the metal with ur charged body. and the amount of current depends on the discharge resistance before and after its formation. which varies during the discharge time. so it doesnt hurt u cuz the values of volts and amperes are too low. and the idea that "a special number of voltage or amperage will automatically kill you" IS definitely ACCURATE.

"who says ... Scuffing your feet across a carpet ... produces high currents???"

People who have measured it. See http://www.wolfsonelectrostatics.com/04_news/index.html#current-and-time

"so it doesnt hurt u cuz the values of volts and amperes are too low."

No, the reason it doesn't hurt you is because the *energy* is too low.

'the idea that "a special number of voltage or amperage will automatically kill you" IS definitely ACCURATE.'

No it's not.

I saw on mythbusters that only a few milliamps across the heart will kill you.
But how much voltage do you have to apply to your body to get milliamps across the heart? And how long of a duration does the current need to last to kill you? if it's 10 milliamps for 1 nanosecond I doubt it will do anything.
chakra endolith4 years ago
WOW!! U sure R a expert on electricity!! where u got all those facts from??
endolith chakra4 years ago
I'm an electrical engineer. :)
dillonxti5 months ago

where is the schematic for the inverter you used

twotower1 year ago
Thanks for your instructable! Since I'm still learning, I'm not up on all of the abbreviations. Can you please tell me what 'RB' stands for? Certainly not Rhythm & Blues...."humor"
Thanks!

Rb = Ballasting Resistor

jeanrenaud5 months ago

Hi, i've made a 5 stage Marx Generator, with initial voltage ±10 kV (hard to tell i can't measure it reliably, but it's a CRT monitor flyback).

After some experiments, all the resistors between stages blew out (my ohmmeter shows "OL"). In your instructable, you used 1M 500V 2W carbon resistors. I've choosen 1.8M 1W 3.5 kV metal film resistors. I'm not sure how this happened ;)

My ballast resistors (rated 10kV) are still ok.

Any idea, guys ? I don't blame anybody but myself ;) but some opinions are welcome.

Jan_Henrik5 months ago

SNAP... YAY sparks! :D

DrZoiberg6 months ago

I made it,but i have only 2cm long spark why????

eerambach7 months ago

What sort of amperage and voltage do you put into it? I was hoping maybe an electric flyswatter would be enough for a really small one.

Magnetron8 months ago
I love this very cool and simple to build
W I N G M A N9 months ago

Could this be connected to a inductor coil and be used as an EMP generator?

Fayez slim9 months ago

can i use a ceramic capacitor rated with 2000v inside 4000v because i cant find 4000v ceramic capacitor

Eternal661 year ago
cool man!
pacina1 year ago
Hey I just built this and the power supply but I have a question before I put any power to it how do I fully discharge it after words so it is safe to touch again, I know with a normal capacitor you just short out the ends is it the same with this??? and is there any way I can add a dummy resistor into it somewhere that will just drain the power away itself when the power is turned off.
Thanks in advance Pacina
Hasan771 year ago
I have a question if you don't mind, what guaranties that the spark gap won't fire before the capacitor is fully charged, if i'm charging to 8 kv isn't it possible that the spark gap fire at 5kv for example?
You just have to adjust the gaps until you get the maximum spark.
Hasan771 year ago
very helpful, very clear,Thanks a lot !
noahbarr1 year ago
what if i made one of these with two 330 micro farad 200 volt Reservoir capacitors from a power supply
my wookie1 year ago
just for fun and because i could, do you think a MOT would work to power it? figured id just ask if you thought it would be safe. (don't want to blow up a bunch of capacitors, not because i'm cheap, just because it stinks)
Lord Garon1 year ago
Guys, let me offer a little advice in the hopes of preventing unnecessary injury. I was an electronics technician in the military and maintained high power communications and radar equipment. I have received two serious shocks, both causing heart fibrillation and requiring emergency medical care. One was from a -350 VDC bias supply on a CRT radar display and the other from a +1800 VDC plate supply. Both were my fault and were caused by a failure to follow safety procedures which I was well aware of. (Okay, I acted stupidly.)

The worst case electric shock scenario involves a circuit completed through your heart via direct contact with blood in vessels. An unlikely event which would require piercing the skin at two points. However, the scenario shows how sensitive your heart is to electrical disruptions; a 1 milliamp DC current flow can initiate fibrillation and 10ma can be fatal (arrest). On a more realistic scale, I can personally vouch that a 350 volt potential across dry skin can send you to the hospital with a team of very worried paramedics. Of course, the current level is important, but if you can't compute the possible current flow, assume it is dangerous.

My advice: Reduce the chance of a complete circuit through your heart. How? Observe the "One Hand" rule. When working around an energized (or recently energized circuit with capacitors), put one hand in your pocket. The current path from fingertip to fingertip is across and through your chest. High voltage will find a way to conduct, regardless, and the One Hand rule is NOT a cure-all, but it is a good start for safety.

If you are not familiar with basic electrical theory and safety precautions, if you don't know WHY a circuit is either safe or dangerous, don't play with it. Period. I have a machine at home that will make almost as impressive a spark as this one and is electrostatic in nature (microamp currents from a PVC charging rod and a few water bottle/foil Leyden jars.) It HURTS, but I don't think it would kill me.

If in doubt, just remember that TASER guns run off batteries and people have experienced fibrillation and heart attacks from being tased. And TASERs are designed NOT to kill.

Sorry for the WOT, but it seems important to me.
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