I plan on making a coilgun, I heard I can get camera capacitors for free to use on it but they have a lower capacitance than I want for it. Do you know of an easy way to get a higher capacitance capacitor for cheap, my goal is 6800uf since I looked at a few videos with coilguns that used that and had about as much power as I want. Also any other tips for making one, Ive been checking the laws to ensure its legal.

I’m not sure what a coilgun is. Make sure it supports the voltage you need, and that you don’t need an unpolarized one.
Is $1.59 plus shipping from Jameco cheap enough?

I dont think the voltage will be high enough but I will check when I get more posts to tell me more. BTW a coilgun is basically a gun that uses electromagnetism to launch projectiles using a coiled wire. BTW it is legal in the US.

If you want any sort of appreciable force behind the projectile you’re going to need some pretty large capacitors. Obviously this scales depending on the size of the projectile you’re trying to shoot and how fast you want to shoot it, but keep in mind that the average Coilgun is only <10% efficient. Here’s an example of a project I saw on YouTube a while ago:

Alternatively, if you wanted to avoid capacitors you could look into something like a Gauss Gun which operates under similar principals but is a bit more complicated to wire:

As far as legality goes, I’m not sure if these are actually considered “firearms” but in either case, the law allows you to manufacture them as long as you do not sell/give it to anyone else (otherwise you would need an FFL which is hard to get and expensive). If they are considered firearms your municipality may have ordinances about where you can fire them.

Cheap electronic stuff though it’s often really assorted and random:

I found others online up to 80V at real electronics parts, and 120V on ebay. If you find a capacitor that is not quite that large but within an order of magnitude, you can put capacitors in parallel to increase their value with the same max voltage. Capacitors in series increase voltage but decrease capacitance.

In any case, be VERY careful! Current kills, and large capacitors are great at providing large currents. In addition to insulating everything, include a “leaker” resistor so that when if you turn the thing off while it’s charged, that energy will be safely dissipated as heat. Never assume a capacitor is discharged - put a voltmeter on it first!

BTW in Massachusetts they are not considered firearms, but just in case I’m gonna talk to some officers I know. Also I think I’ll stick with a coil gun because I want to learn more about capacitors.

Thanks all you for the information.

Be careful with this.
Many states have catch all laws they can deploy when they do not have an explicit law.

Don’t forget to make out, or update, your will and your insurance policies.

I remember finding 10000uf and 12000uf 400V capacitors on Ebay for a similar project, 2 for $50. Those plus a 12V to 240V inverter and some diodes will charge them up petty fast.
EDIT: Looks like they’re all gone. Still, Ebay has pretty cheap caps.

These guys have 500V capacitors in the range you are looking for, and they run about $7.

Do you think this capacitor will work

Repeating the warning from GeeTwo: capacitors can be lethal. They store charge for a very long time. Please learn about the safety rules and be extremely careful.

I made a coil gun as my senior class project in college many years ago. The amount of energy needed was scary.


Stay safe!

The amount of energy stored in a capacitor is proportional to the capacitance value and the SQUARE of the voltage applied. Anything over 50 V is considered to be hazardous in industry. You should be verifying that the voltage across the capacitor is safe, each time, before doing any work on your circuit.

Commonly available wire typically has insulation rated for 300 V. Some of the posts here are talking about capacitors rated for much higher voltages. There are also construction techniques that must be applied to ensure that the circuit you build is safe.

With the size of capacitors you will be using, you should start with installing a bleeder resistor across it so that it will discharge the capacitor (bank) within a few minutes. The resistor will need to have a sufficient power rating (with adequate margin) to withstand the operating voltage being applied constantly.

If you do not know how to do the above, it would be best if you get some on-site professional help and learn on some less hazardous projects before starting on this one.

I am closing this thread because this discussion pertains to the creation of a weapon, which is not appropriate for a high school robotics competition discussion forum. Legal or otherwise, Chief Delphi is not the place to discuss the details of the creation of weapons.