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# Need help picking correct capacitors for coilgun? Answered

My coil gun right now is using ten 330v 100uf flash capacitors from disposable cameras. They are being charged by the flash circuit on a camera. I am looking to upgrade the capacitors for more power and I wasn't sure which ones to get. I want the strongest ones that the flash circuit will be able to power. Any recommendations would be very helpful.

,Thanks!

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## Discussions

remember Energy = CV^2/2 - increasing capacitance isn't as effective as increasing volts.

I tried to increase the voltage by connecting my capacitors in a series. They charged very quickly and the projectile hardly made it out of the barrel. I have no idea what the problem is. Remember I'm using the camera charging circuit. if the charger is the problem can you suggest a better charger circuit? Thanks!

Connecting capacitors in series won't increase the energy output, it will cut it. Ceq = (1/C1) + (1/C2) + ..........
You can think of it like resistors in parallel: If you have 2 resistors in parallel, both with a resistance of 10 ohms, the resistance of the circuit as a whole will only be 5 ohms. I believe the same is true for capacitors in series.
Also, (I may be wrong but) You cannot hook capacitors together in series to increase the voltage output. If you put 120 V into a capacitor, it will output 120 V. It doesn't matter how long you charge it or how many you connect: as long as your supply is providing 120 V, it will ALWAYS charge to 120 V.

So what you've done by connecting your capacitors in series is cut the total capacitance by 1/10, (thus the reason they charged so fast) and kept the supply voltage the same. If you want more energy, you need a more powerful supply. You can also add more capacitors, but like steve said above, increasing the voltage is the most effective way.

so my best bet would be to get more powerful capacitors and power supply? I thought I remembered something about capacitors in series doubling voltage as well as decreasing capacitance but I guess not. Thanks though!

Add more caps, which can still be 330 V, but add them in series/parallel banks.

Doubling the voltage would take twice as many caps, but the energy would increase x 4.

So two parallel banks of 10 or 3 banks of seven linked together in series would give me better power?

More C is good, more V even better. Do the maths yourself.

C in series, total C = C/ number of caps C in parallel C= number of caps * C

Steve