Instructables
This is roughly as powerful a coil gun as you can make using a standard mains switch. To make a more powerful coil gun you will need a higher rated switch, preferably solid state.

Through much research I found all the Variables that affect the efficiency of a coil gun:

Projectile
Length
Stabilisation
Diameter
Length to diameter ratio
Material
Conductivity
Aerodynamics
Initial Positioning
Mass
Flux Linkage

Coil
Length
Number of layers
Thickness of wire
Flux linkage

Current Pulse length
Switch bounce and resistance
Capacitor Voltage and Capacitance
Overall wire length and diameter used.

Also there are several ways to increase standard performance using:
Optical, Inductive or Physical Triggering
Multiple stages
Super cooling

 
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Step 1: The Plan

Picture of The Plan
I had some 6mm steel bar, some 6mm plastic pipe, a micro switch and some enamel coated wire as a starting point.

I took apart 17 disposable cameras and soldered the capacitors in parallel to form a capacitor bank of 1360uF 330v which using E=1/2CV^2 gives a stored energy of 73J.

I used one of the camera circuits as a charging circuit by removing the flash, removing the trigger switch and soldering the charge switch closed.

I then used an old mains PSU switch as a charging switch although any switch will do. The whole circuit was covered thouroughly in insulation tape and put in the only plastic box of the right size I could find at the time; An empty Bertolli spread box.

I wrapped a coil out of 26AWG enamel coated wire 30mm long and 7 layers thick. This is because the coil should be the same length as the projectile and the projectile should be five times longer than it is wide, hence 5x6=30. The number of layers is dependant on wire thickness and capacitor bank size and voltage. The thinner the wire, the smaller the bank, the less layers. wire too thin will impede flow and maybe burn out. Wire too thick will mean you have less coil density than is potentially attainable.

Simulations ran well after the device was constructed reveal this isn't an optimal design and there is some 'suck back' as you can see on the graph when the turquoise line falls bellow the axis suddenly.
jbyrns19939 months ago
Could one use a 100K uF 600V cap in place of the photo caps?
al 011 year ago
how fast is that Ben?
supinder1 year ago
can you add a fly-back transformer from a tv instead
csphar1 year ago
I have 962 uf and 2640 v is that good?
LetsBuildOne (author) 1 year ago
The energy stored in a capacitor is = 0.5*capacitance (Farads)*Voltage*Voltage. So for your Capacitor it would be 0.5*2100*2100*0.000001=2.205J. In comparison, the one in this Instructable is 73J. Having said this even 0.01J would accelerate something, it would just have to be very small, light and it wouldn't go very fast.

Put simply: Yes it will work, but it will be pretty pathetic. Almost Certainly not worth doing. You would probably be better using a Car battery charger or an ATX powersupply or even some lipo batteries.
I have one 400V 2.2uF capacitor but no camera circuit can i still make a coil gun
LetsBuildOne (author)  tawhidiscool1 year ago
Not really, you only have 0.362 J of energy which is less than 1.7% the power mine has. It wouldn't be very powerful... you can charge it using any dc voltage source. A rectified 12v to 230v inverter would charge it to roughly full voltage. This is dangerous though and I do not recommend it.
Pizzapie5002 years ago
I have one 20V 1500 uF capacitor. Will it alone work?
LetsBuildOne (author)  Pizzapie5002 years ago
Yes, but don't expect the power I have. You will have less than 1%. of that.
Bretta9mm2 years ago
Could I use your graph photos for a project? You will be credited and referred to.
LetsBuildOne (author)  Bretta9mm2 years ago
Of course. If you want me to plug your coil gun parameters into my simulator and make a graph for your coil gun then I can do that for you as well.
Bretta9mm2 years ago
Can you tell me were to get your stuff like the psu switch and the 6mm bar. I am having a hard time finding some.
LetsBuildOne (author)  Bretta9mm2 years ago
You can use large nails instead of the 6mm bar but that should be available at your local hardware store, I believe mine may have been left over from a guitar stand project I did a while back. If so I got it from B&Q. Focus and Do It All should also have some.

The PSU switch is just a switch, any switch will do. Mine was out of an old computer power supply unit (PSU) I used to get broken ones free from the IT support department at the university. Your schools IT department may have one. If so be careful when dismantling as the have high voltage capacitors in them. If in doubt, consult a responsible adult and or chicken out. Better to not have the parts than be dead.
On your circuit diagram I see this 'Reverse Voltage Protection Diode'. I am not sure what that is. You don't mention it in the textual instructions and I'm wondering if it is required.
LetsBuildOne (author)  Bretta9mm2 years ago
It isn't required but it is highly recommended. It is just a normal diode like you would use in a Wheatstone bridge to rectify mains AC into DC.

The coil gun system is very similar to a transformer. When you dump all that electricity into the coil a massive magnetic field is generated around the coil which is was attracts the ferrous projectile into the coil. When the electricity runs out or the switch is broken, the magnetic field collapses and the projectile de-saturates. This is how a transformer works, The varying magnetic field induces a current in the coil. So when the field collapses a current is induced which can break your components such as capacitors by charging them backwards. The diode is there so that the electricity can go back into the coil and dissipate rather than frying your expensive caps and solid state switches.
Bretta9mm2 years ago
What is a microswitch and what type should i use. I dont see any information about the microswitch you used.
LetsBuildOne (author)  Bretta9mm2 years ago
Google is your friend; A microswitch is a small switch that is usually rated to mains voltage and relatively ample currents. Around 240v-12A. They aren't usually used directly but rather via a door, latch or cover. An example of one is here:

http://www.maplin.co.uk/low-cost-standard-microswitches-6453
kgaurkhede3 years ago
then suggest me some effective charger for caps but not the disposable camera one thanks!
LetsBuildOne (author)  kgaurkhede3 years ago
Which country do you live in? or more importantly what voltage is your mains electricity? Assuming it is in the order of the 50Hz 240v RMS that we get in the UK you should be able to use half or full wave rectified mains electricity to charge them though I wouldn't recommend it as it is inherently dangerous.

I would suggest you use a 12v to 240v inverter and a small battery as your power source rather than messing with the actual mains though as mains is incredibly dangerous as it happens to be at roughly the right AC frequency to stop your heart and there's an unlimited supply of it out of a socket.

You should use half wave rectification to limit the power available and put a reasonably large charge resistor in the way to stop the cap charging too quickly. I have used a standard 40W bayonet light bulb for that previously because it offers non-linear charge resistance. Make sure it's all in a double insulated box and you need a tool to open it. No metal touchable on the outside etc. Check my 50cal for instructions. That is the charge circuit I used on it.


kgaurkhede3 years ago
can we charge capacitors using a battery charger
LetsBuildOne (author)  kgaurkhede3 years ago
Capacitors need charging with DC and you must NOT over charge them. i.e. do not charge a 20v capacitor with a 30v charger, they have a habit of going *POP* which can be dangerous. You need to check if they're electrolytic capacitors too as they have a charge polarity and need to be wired up in the right direction otherwise they'll *POP*. The only other thing to look out for is charge current. Most capacitors can charge much faster than batteries but if you charge them too fast they will get hot and either damage them selves or *POP*.

In plain English; Yes, but I would need to know the specifics of the charger and the capacitor being charged and how you intend to do the charging. Monitoring the temperature of the capacitor and the voltage across the capacitor is important when using a charger not intended for capacitors as to avoid damaging you or your caps.
fishinigami3 years ago
one more question, how do you know when it's charged?
LetsBuildOne (author)  fishinigami3 years ago
On the original camera flash circuit there is an LED that lights up when it's about fully charged. This still works and you can see it as the red dot between the charge switch and fire button on my coilgun.
ooooh... missed that...

thanx! :D
fishinigami3 years ago
could you explain how to hook up the capacitors a little more... you attach them to the 2 little copper bits?
LetsBuildOne (author)  fishinigami3 years ago
Does this help?
Capacitor bank diagram.pngCircuit diagram.png
yes! thank you for taking the time to do this! im gonna try this when i get a chance!
LetsBuildOne (author)  fishinigami3 years ago
No problem! Happy to help!