Introduction: 400 Volt RAIL GUN

Picture of 400 Volt RAIL GUN

For this instructable I will explain how to make a simple rail gun, firing metal ballbearings. However, the parts are not to expensive, but im not sure of how much it all came to as I built it at my school during DT lessons. There are more powerful versions, but this doesn't take long to build and is quite effective.
It is not very neat, but I didn't have much time as it was only meant to be an alternative way of building an airsoft gun using a new system (part of my GCSE project). My design fired 9mm steel ball bearings, which is fun, but can cause injury.
This does use voltages upto 400V, and comnpressed air, so be carefull, and never put anyone at risk from whatever you manage to create.

The railgun is a form of linear accelerator, using a electromagnetic force to propell an object. The way that these work is that a electrical current is conducted up one rail, across the projectile, and then back down the other rail (see picture). This is called the Lorenz force.

Please ask if you have any questions.

This is my first instrucatble, so please be nice...

Step 1: Parts

Picture of Parts

Most of this project can be changed, so you don't have to use these exact parts, but these are what I used for mine.

For the Compressed air system;                                                         (step 4)
             Gas reservoir- I used 4 small one, but a large single would be perfect, or use a spring.
             2 gas valves- 2 gives a faster rate of flow, but not necessary if using a spring.
             Pneumatics pipes- reservoir to valve to barrel connections
             Steel tube (barrel)- diameter must be similar but slightly larger than you projectile.

For electrical (the rail gun)
            I used 10 400 volt 450uf aluminium electrolyte capacitors (step 2)
            Solid aluminium bar (for rails)- 20cm x 3cm x 3cm              (step 3)
            Acrylic 20cm x 3cm x 0.2cm

Step 2: The Capacitors

Picture of The Capacitors

For my design, I used 8, 400V, 470uf capacitors connected in parrallel. This gives a total capacitance of 3600uf, but still at 400 volts. However, charging them off a 9 volt battery will only give you 9 volts output. To charge these to 400 volts, you can use two different methods.

You can do the more dangerous way (don't unless you actually do know exactly what your doing) of putting the correct step-up transformer into a plug socket and then adding a semi-conductor diode
[Capacitors must be charged using DC current, not AC, aluminium electrolite capacitors can only be charged in one direction, else they can heatup, melt, or explode].

I would not really recommend going anywhere near the mains and sticking stuff in, so the best option is to build, or even better, buy a DC/AC converter (there are lots of small car converters you can buy that run on 12v batteries), and then connect a transformer to the output, and add a semi-conductor diode to change it back to DC power. This is probably the cheapest and easyest option.

You can also use the flash circuit from disposable cameras, but to charge 8 capacitors of this size, I would need quite a few or risk burning the circuit, and disposable cameras aren't that cheap and shops now send them off somewhere after use, so I couldn't get any used ones.

Step 3: Rails

Picture of Rails

The usual way is to use two parrellel metal strips, with a gap just large enough for your projectile. However, this provides a poor connection area between your projectil and rail, and can cause more sparks and therefore faster errosion to your rails. My design used a solid aluminium bars about 20cm x 3cm x 1.5cm.

I clamped these togeather, with a sheet of perspex between the two. Then, I drilled down the center of the two blocks and perspex, with a drill bit slightly larger than my projectile, forming a abrrel with two metal sides with a plastic insulation between the two. I did this 3 times, and the put the three sections togeather to form one long barrel/rail.

Aluminium was probably not a very good choice in material as it is quite soft (compared to steel), and can be damaged easily by any sparks made, with effects the connection between the rail and projectile for the next shot, but it was the easyist metal to work with.

Connect the capacitors, the positive terminal to one rail, negative to the other.

Step 4: Pneumatics

Picture of Pneumatics

The metal projectile cannot simply be inserted into the rails, as you'll get electrocuted, and the projectile will get spot welded onto the the rails by the large electrical charge suddenly jumping across the projectile.

To prevent both of these things happening, the projectile must already be moving befor it meets the rails at a sufficient speed to prevent it stopping. My system used 4 small gas reservoirs (you can use one, but these were all i had at the time, and my other large cylinder was attached to another project). I charged mine to around 120PSI, but the amount of pressure you need depends on the weight of your projectile. I didn't need such a high pressure, but it was more fun this way.

You don't have to used compressed air, but this was the quickest and easyest way for me as I only had to put the components togeather instead of build any parts.

You simply need to connect  your cylinder to a valve, and then the valve to the barrel (this valve also acts as the trigger) and some way of refilling your cylinder (another valve connected to an aircompressor or foot pump), and a plastic barrel that is a tight fit with your projectile. The end of your barrel should feed directly into the rails.

You can add some sort of breach, but as this was a prototype for my main GCSE project (an airsoft gun) I only needed proof of concept, so didn't have enough time to bother with one.

Step 5: Final

Picture of Final

Put it all togeather, and you should have a working (or not) railgun. Don't point it at anyone, and discharged the capacitors befor handling after each shot as they don't always full discharge. Just place a screwdriver over the rails to complete the circuit as the projectile would have done. Also, after charging the capacitors, you must disconnect them from the charger as they will discharge back into the transformer. This isn't really a problem except you will loose power befor you shoot.

My video is only using 30volts, because at that point I did not have a DC/AC converter, but the result is still quite good, with some nice sparks coming from the end of the rails, and the person who does the "Oh my..." is not me, just a friend watching.

I actually now have 10 400 volt 480uf capacitors (I forgot about the last two). This, when charged to 400 volts, produces 360 joules of energy, which is capable (excluding resistance, friction, all the other stuff) of 1011.26 m/s, but as this is actually a very inefficient design, the actual velocity will be a lot less.

I now have a inverter, but having a few problem as the voltage output is over 2000 volts, and AC, so i'm trying to get a transformer to lower it to 400 volts, and buy a rectifier diode to convert it back to DC.but it will be mounted to my actual GCSE project (an airsoft gun) so will use new rails and a 6mm copper-coated airsoft BB. Unfortunately, this means the video won't be ready untill some time after easter hols.

Step 6: New Project

Picture of New Project

My GCSE project has finally been finished, but not tested as the physics department wouldn't let me use thier 400 volt power supply to test it with (for the capacitors) and i'm still working on my DC/DC inverter. However, it is made for airsoft (but it has to use 6mm steel ballbearings. It works the same way as the prototype (the railgun described earlier), but with a loading mechanism and a better compressed air system, making it a bolt action sniper.
This will be my next instructable, but will take a long time to make, as the total parts are around 70, plus the pneumatic and electric circuits (very simple).

Unfortunately, i'm not sure if i'll ever be able to test my project as my physics department has a power supply that goes to 400 volts, but are worried about safety, ethics, legality... but i'll ever get my DC/AC inverter and do it that way, or use cameras.

The pictures I have uploaded of my airsoft gun are old, as it fell off the shelf 2 weeks befor being marked (hitting a computer, edge of table and the arm of a chair) so had to be completely rebuilt, but most of the individual parts weren't to damaged, but it looks slightly different, and better now, and has a bi-pod attached to it, unfortunately all the photos are still on the school's computer, and i'm now on holiday, so they won't be up for a while.

Step 7: Next Project

For my A2, i'm hoping to change the coil gun/ rail gun idea and mix it with some ideas from the particle colliders. I will be making an oval section of tubing, about a metre long, and wrapping the entire thing in 8swg enamelled copper wire (if i can find enough). This will be done in about 10 sections, so if one melts, then I don't have to replace the entire lot. These will be connected to 40 amp continuous dc power supplies, with a ball bearing inside the tubes. Then, playing with about 10 different capacitor packs and light gates, I hope to be able to get the ball bearing (always hopeful) to 340m/s, the speed of sound! Hopefully, the physics department will be more supportive of this project and help me with the power supplies. Then, the tubing will be surrounded in a shell of aero-gel, and providing the physics department like my project, filled with CO2 (not liquid as it turns from solid to gas almost instantly) to about -78 C. There will also be a small gap either side of the oval so you can see inside the tube, and so the light gate can measure the speed. So, if its built well, wrapped with 3 layers of copper (a total of about  50m of wire), cooled sufficiently, and the right amount of power used, it should be attainable. If not, it'll look awesome anyway. But, that'll take another year, and won't truly be started until after the summer. 

More to follow...... after exams!! yay


FauziTheExplorer (author)2015-09-26

can i use less than ten capacitors i mean like 5 or 3 just asking

Theoretically, yes. However, you will only be getting 1/2 to 1/3 the power, which may not be enough to drive your projectile.

ToạiĐ (author)2016-09-07

This thing uses DC or AC?

CadeConnelly (author)ToạiĐ2017-05-22

DC, AC will blow the capacitors.

JamesB527 (author)2016-07-03

Could a 20volt 1 Farad capacitor be used for this build?

CadeConnelly (author)JamesB5272017-05-22

No, not nearly enough power. Use this to see how many joules of power the capacitor holds:

Unless you broke physics, your efficiency is going to be terrible (I've been calculating .5% in my design), so you need a lot of energy to start with. You also need enough voltage to make a good arc, so you probably need something at least in the 300v range.

bloodwriter (author)2016-04-21

a cool idea would be a farnsworth fusor but there really expensive if you want actual results

metronome (author)2015-06-10

try making a 400V boost converter . It has a good efficiency ( about 40%) and you can also control the output voltage(from 300V to 500V).its not very cheap but its so small and portable.

here is a very helpful boost converter

I hope it helped you!

cubj71 (author)2012-03-01

hey if the projectile does not move try to hook up capacitors in parallel, so you get more microfarads. not in series.

HansB3 (author)cubj712015-06-03

how about a marx generator? or am i crazy?

indra810 (author)2011-05-25


I already trying to build one. But when i'm firing it, the ball bearing was not sped like your's.

In my design, i use two parallel aluminium strip and the gap between 2 rails is 2.1 cm and the diameter of the ball bearing is 2 cm. so,what i want to know is, does the ball bearing and the rail need to touch each other when it is fired ??

Thanks !!

Jlesko (author)indra8102015-01-11

So I made a rail gun last year for science fair and when I made it I used .25 steel balls. the distance between my rails was .252 .

minisojo (author)indra8102011-05-25

Preferably, yes, they need to touch, other it might not get a constant current flowing through, and there will be more arching, which will erode your rails faster and result in even less contact. It should work without them touching, as long as the current can jump the gaps, but probably not as well.

keith.t.greco (author)2015-01-08

Oh my... Yes, this helped me so much. I am currently in the process of building a railgun similar to yours, but on a larger scale, and I needed help with a lot heading into this project, but this guide really helped me and it shown some important problems that I haven't put any thought into yet. Currently, I am cutting aircraft grade aluminum I received as a donation, and planning how I'm going to insert the capacitors into the back,, and basically, it's really tough stuff. So I'd like to thank you for the help on this, it's nice to know someone did something similar to us.

(unfortunately, I don't have images yet, but I'll be sure to show you in the comments once I do!)

Tobor 2.0 (author)2013-04-22

you could use diodes for the problem of energy going back into the transformer issue you mentioned.

droryuditski (author)Tobor 2.02014-11-24

You kidding me? Pneumatics?
You could make a regular spring magazine so every shot it will reload automatically(unlike in regular ARs, which require the gas to push the bolt back).

droryuditski (author)Tobor 2.02014-11-24

You kidding me? Pneumatics?
You could make a regular spring magazine so every shot it will reload automatically(unlike in regular ARs, which require the gas to push the bolt back).

simplebotics (author)2013-05-24

Halo Forerunner weaponry!

soulassassyn777 (author)2012-02-16

The answer is... a paintball gun.

crazyjp got me thinking though... If you use the paintball gun as the initial means of propulsion and then build a rail gun around it, would it work? Like a "sleeve" that you bolt in place over the barrel with all the caps and wiring built in, all you will then need to do is find a way to activate the circuit automatically once the paintball gun has fired. You might have to cut down the barrel though, the standard barrel should be okay since they're mostly quite short and useless anyway.

The loading problem has also then been solved as most paintball guns are semi-automatic and have hoppers attached, all you need is a the correct diameter projectiles.

You might need some kind of separate battery-pack or else things will get real heavy. Unless you can find some small, light, long-lasting, high-voltage batteries.

crazyjp (author)2011-10-29

if your using compressed air wouldnt it be simpler top just take the compress air hose hook it up to a barrel that just barely lets your projectile slide through put a notch in the spot were you want to load the projectile adn get a piece of tube that will slide over the spot where you load the projectile ad have some type of triger that when pulled causes the compressed air to be shhot into the barrel forcing the projectile out the end of the barrel and just demolising what ever you were aiming at??? i mean sure making a rail gun would be bitchin but you would also have to deall with some type of power source that can create 400volts verse just an air tank you strap to your back and refill off of a 120 volt air compressor?? i dont know if im wrong when it comes to thinking that the gun would be lighter if its just powered off of compressed air than having a bunch of batterys and capaactiors and metal rails

techno guy (author)2011-10-10

Mine didnt work!!!!! I built one and charrged it up to 60 volts and I started it by rolling it and as soon as I applied the voltage, it stopped on the track. And it did that even when I reversed the polarity. How can I make it work?

akinich (author)2011-08-16

Hey dude nice instructable
i kinda need help asap!
i built a mixture of ur instructable and from how to make a railgun
i have 5 caps of rating 250v and 680uF each
that comes to about 3400uf
the rail type is from the other instructable
the main thing is that i am not able to fire anything
the voltages i used are from 7.5 to 12 v
i need help asap
oh yeah btw i used hack saw blades as rails ( removed the paint )
and no launch mechanism
thanks in advance!!!!

hahaha55 (author)2011-05-10


I'm trying to build one of these for a school project. I plan on only using a small voltage (30V), like the one in your video, but I am having a hard time finding the right capacitors.

What if I have 45 100uF 35v capacitors @30V? Would that be enough to mimic what I saw in the video with only 30V and 10 450uF capacitors?


hahaha55 (author)hahaha552011-05-10

I found cheap 390uF 200V Electrolytic Capacitors. Would these work in place of your 450uf 400V ones if I used 12 of them instead of 10?

minisojo (author)hahaha552011-05-11

Yep, they'll work fine. If you can find a higher power supply then things will really start to happen. Although, I think in mine, quite a bit of the speed came from the compressed air, so a higher voltage would work better and look much better. I'm just updating with my next new project i'm making for my A2 after the summer. yay

indra810 (author)2011-04-14


Right now, i am trying to build a railgun for my school project.

I want to know about the semi-conductor diode that you used for your project. What type it is ??

And for the rail, if i use two parallel copper strip (75 cm x 5 cm x 0.5 cm), will it work ??

Thank you before....

minisojo (author)indra8102011-04-16

Copper will work better than the aluminium I used, as for the diodes, I got mine out of a plug socket adapter for a mobile, but I think I have destroyed them with whatever I put through them, but, I think, although the ratings will be low, you can use diodes out of a plug adapter as your current will be much lower than the plug sockets, and even though your voltage will probably be much higher, they should survive, but I'm not completely sure. Or, for something simpler, use a rectifier instead of a diode, because they have a very high voltage and current rating, and I think you only need one to convert from AC to DC, but, you may want to check this before you try, because I could be completely wrong.

fjpalacios1 (author)2011-03-29

Working on it....thanks!

nadams-2 (author)2011-03-09

hey so i tried building a rail gun and all i got out of it was alittle plasma. okay, my question is will a 4 farad capacitor work in place of the 8 capacitors?

minisojo (author)nadams-22011-03-10

Hi. What voltage did you charge the capacitor with, as this will limit the power and length of time the capacitor discharges in, cause 4 farad is massive, but that sounds like a supercapacitor, which normally will not have a large enough voltage be as effective, or the other cause i can think of is that your projectile isn't entering the rails fast enough and is sticking to the rails as the electricity arcs between rail and projectile. Hope this helps a bit.

Reach (author)2011-02-03

What is the biggest thing you can shoot out of it? Or does it no shoot anything.

minisojo (author)Reach2011-02-04

You can make it to shoot any size (power and materials depending), but mine was firing 9mm ball bearings, but 6mm for my new one.

Rhanyc (author)2011-02-01

Hey, I'm actually quite eager seeing the video were you put 400 Volts through it. Is it coming soon or weren't you able to use 400 Volts?

minisojo (author)Rhanyc2011-02-02

Unfortunately, i had to take apart my rail gun to use the parts in the airsoft gun, but, I am putting it back togeather in the next couple of months, with a few additions, and with any luck, finish the power supply, it shouldn't take to long, and the power supply shouldn't be to much of a problem, so look back in a month and hopefully i'll have something to update this with. Sorry I haven't been able to do this sooner.

REA (author)2010-03-18

rather than an air compressor, cant you get away with using a spring to propel the projectile toward the rails?

minisojo (author)REA2010-03-24

Sorry i've been slow replying
A spring should be fine to use, the ball bearing just needs to be moving fast enough not to get welded to the rails.
The projectile I used was about 0.7 grams, but i'm not sure because the packet didn't say as most steel ballbearings aren't usually used as projectiles. Unfortunately I never got a chance to measure the velocity untill I needed the capacitors for my actually project, but in 3 or 4 weeks I should be able to give a speed for one firing a 6mm ball bearing with hopefully 400 volts.

odiekokee (author)minisojo2010-08-12

Would you have a good idea whether higher capacity or voltage would produce higher velocity? I'm finding lots of 400 and 450 v caps, but to get up over 300uF starts getting expensive. I found some 10KuF 450V but I can't see putting $35 each into them. Suggestions?

REA (author)odiekokee2010-08-12

ive seen 9 F (9000uF) capacitors for about 10 dollars (forgot where though). you could try going to a computer part recycling place and salvage some capacitors from a motherboard. most of the time they will be somewhere around 2.2 F.

sandito (author)REA2011-01-18

uF mean micro farad or millionth so a 9 Farad cap would be 9000000uF

REA (author)sandito2011-01-18

thanks. my grasp on the metric system starts to dwindle after milli (cant quite process that many zeros).

minisojo (author)odiekokee2010-08-12

The higher the capacitance, the more energy it can store, so the higher the capacitance the longer it takes to discharge or the higher the charge given out. The voltage will be how high a voltage ytou can charge it with (it will give out the same voltage as it is charged, so buy capacitors with a voltage slightly higher than what you want to put in. My physics departement had a 400 volt power supply so I used 400 volts, but at the end they decicded not to let me test it with the full 400 volts). But a 300 uf 100 volt capacitor stores the same potential energy as a 100 uf 300 volt capacitor. But, befor you spend any money you may want to try and find a bit more out about capacitors so you buy what you need.

REA (author)minisojo2010-03-24

i plan on firing pennies, as they are coated with a diamagnet (copper), and also because they are abundant, cheep (1¢ per shot lol), and wont take to much force to get a decent speed, as it is light.

minisojo (author)REA2010-03-25

That sounds like a good idea, but making a tight fit barrel and when using a high voltage, stopping the electrical current jumping across the two rails might be more difficult, but that does sound awesome.

Speedmite (author)2010-08-16

I was thinking, use steel ball bearings that are 6mm and use an airsoft gun, but my problem is i dont know where to get the cameras. They ship them off at walmart, whitch leads me to belive other chain stores like walgreens are doing it too. So where did you get yours, and do I have to go to some odd camera store?

sandito (author)Speedmite2011-01-18

Blacks Cameras

minisojo (author)Speedmite2010-08-26

Unfortunately, I think most places now recycle the disposable cameras, so I think you will either have to buy a new disposable camera and take it apart, or build your own DC/AC converter. I didn't use cameras, I used a converter from a cathode tube light, unfortunately, this is a little more complicated as it produces over 2000 volts, and it still needs converting back to DC.

sandito (author)2011-01-18

the only place that doesn't get rid of old disposable cameras right away is blacks.

I called every camera store in Vancouver, Blacks was the only one with a box of them.

They said that they like to keep them to go and smash, so they gave me 20 for free

bartj (author)2010-12-28

A question and a comment.

1) How do you switch the power from the caps to the rails or are they always connected together?

2) Somewhere in the comments someone says:

"...But a 300 uf 100 volt capacitor stores the same potential energy as a 100 uf 300 volt capacitor...."

The actual formula for energy stored in a cap is 1/2 * C * V^2

300uf 100 v cap = 1/2 * .0003 F * 100 ^ 2 = 1.5 Joules
100 Uf 300 c cap = 1/2 * .0001 F * 300 ^ = 4.5 Joules

Thus, go for a higher voltage as the energy stored is related to the square of the voltage.

minisojo (author)bartj2010-12-29

The rails are always connected to the capacitors, the projectile is the thing that completes the circuit, and yep, forgot about that, thanks for the correction. It was my mistake, i hope it didn't cause anyone any problems.

adoesker (author)2010-12-16

oh and i don't recommend charging your caps to the rating, they like to explode, try a bit below for safety, if you go with ac-dc transformer system, they tend to get heavy, but if you do a quick fix is to take any household tranny get some high rated diodes you can rectify the ac to dc with 4 in a diamond shape.

About This Instructable




More by minisojo:400 volt RAIL GUN
Add instructable to: