Author Options:

need help for coil gun Answered

i want to make coil for coil gun.i have 21awg copper wire (0.7mm), 250v 10000 microfarad capacitor.How many layer for the best velocity ?


You want a cap with alot lower Farad rating.  Something in the range of 1uF to 300uF is the absolute best.  As for layers, you may need to play around a bit.  Look at some instructables on the website already and use their data.

I would think high capacitance is better. low capacitance doesn't store very much energy. for pulse length, and power of the pulse, it all depends on the actual capacitor construction, though for this application, discharge speed isn't as crucial. pulse-rated capacitors are the best for this, but they're really really expensive.

You want high voltage, low farad rated capacitors. If they are rated to high the projectile will just stick to the electromagnet/coil. Think of it like this, if you have a capacitor with a high farad rating, that means it will discharge over a longer period of time, so it's more like holding a magnet next to the projectile, it will just stick. You want low rated caps so that the magnetic field is only created briefly. There is a certain amount of time you want the magnetic field created for and I know that they use inductors on rail guns to achieve the desired time interval, not increasing the capacitors.

The whole reason people build coil guns out of 300+volt camera flash circuits and high voltage capacitors is because the capacitors discharge that power quickly. If you used capacitors rated at 10 000 uF, the projectile either would stay in the barrel at the coil, or the exit velocity would be minimal and it would not be effective.

quick addition comment. Voltage and coil resistance determines the amperage at high Farad ratings. at low farad ratings, amperage drops early.

well, i believe it also depends on the inductance of the coil and whether or not you use circuitry that forcibly cuts off the capacitor discharge. I'm the kind to use cutoffs to cut power and anti-parallel diodes to soak up the back emf.

if you're not using a control system like such, then small capacitors is most likely the best way to do it, as you have stated.

higher farad rating means that it can maintain the same discharge rate for a longer period of time (you can still control the pulselength though.). C=QV. Q=charge in conductor in terms of coulombs, so it determines the total pool of energy. V is the voltage, as you know. V is what determines the discharge rate (along with capacitor type: electrolytic, ceramic, etc.) i go for high farad ratings because i have a pulselength control system in my design.