Author Options:

Coilgun Capacitor Bank? Answered

I am building a coilgun for a high school project. The capacitors for the original design call for 2200uf 400v capacitors, but these are too expensive. I found some 1000uf 200v capacitors, would these still be powerful enough if I run 5 of them in parallel. Does the voltage make the coil stronger or is it the capacitance. My coil specifications are; 16 AWG 4 layers and 25 turns on each layer




Best Answer 4 years ago

The 2200uf 400v capacitors have an energy capacity of 176 joules, and

the 1000uf 200v capacitors have an energy capacity of only 20 joules !

Based on energy, which bank do you think ?

Will get your coilgun the best projectile ballistic impact ?

http://www.digikey.com/product-detail/en/382LX222M400B092VS/338-2001-ND/2256609 these are the 2200uf 400v capacitors, the thing is it seems like they have 5 leads, how would i wire them?

Depending on the diameter of your cap 40mm or 50mm

There are Positive, Negative and dummy pins at the 5 positions made so the assembly to PCB can't be accidentally reversed !

Don't wire dummy pins to anything ( they are resistively tied to negative ).

Combine the Positive pins.

Combine the Negative pins.


Wow! Thanks a lot it really helped, the capacitors I am going to use are 50mm so i'll be referring to the chart you uploaded, Thank You.

Isn't it easier (smaller and cheaper) to use some 2.7v 100f super capacitors.

My coil gun works on a wall outlet transformer with 12 volts and it launches small paperclips a few feet. i have 400 volt capacitors but they do half the power that the outlet transformer does! HOW DOES THAT WORK!!!! please help

2.7x2.7x100/2 = 364 joules

But these are not rapid discharge capacitors and you will lose a lot of energy through the switch in terms of %voltage lost across the switch.

ie usually an SCR = Silicon Controlled Rectifier = Thyristor has a 1.5v drop which is 1.5/200 = o.75% at 200 volts and 1.5/2.7 = 55.5% at 2.7 volts.

Read it and weep, the low voltage 2.7v coil gun will loose half its energy while high voltage 200v coil gun will only loose 1% of the stored energy !!

Sorry sir if I am bothering you with my question.

But can you tell me is it a bad idea to use a 2.7v 100f super capacitor even if it lost half of its energy because it would still give about 150 joules witch is not bad for a capacitor of small physical size.

Is it the problem that it is not an rapid discharge capacitor ?

Sorry Im not an electronic engineer .

"Super caps are a few Farads, true. But the discharge rate is slow, so I don't think they would be suitable" as primary coil gun drives.

Super caps store lots of energy chemically and loose capacitance as the liquid electrolyte is lost due to evaporation, they have a failure rate above the older high voltage caps.

Well yeah its true.You have made a good point.

If you are replacing one 2200 uF 400 volt capacitor with five 1000 uF 200 volt in parallel then you have 200 joules and a much more powerful capacitor bank.

C + C + C + C + C = Ct

1000 uF + 1000 uF + 1000 uF + 1000 uF + 1000 uF = 5000 uF

(C * V2) /2 = Q or 0.005*2002=200 joules

(C * V2) /2 = Q or 0.0022*4002=176 joules

If you are replacing one 2200 uF 400 volt capacitor with one 1000 uF 200 volt capacitor then you have 20 joules and a less powerful capacitor bank.

(C * V2) /2 = Q or 0.001*2002=20 joules

If you get the $3.38 * 5 = $16.90 verses $19.74 you would save money with the 1000 uF 200 volt and get more power.

I am going to use 4 of the 2200uf caps, but thank you for the calculations, I well keep them for future reference

(C * V2) /2 = Q or (0.005*2002) /2 = 200 joules

(C * V2) /2 = Q or (0.0022*4002) /2 = 176 joules

(C * V2) /2 = Q or (0.001*2002) /2 =20 joules

Coil guns operate on a force of energy called Joules. You can convert joules into any force of energy, such as horse power, etc. The basics of a coil gun operate by storing a lot of Joules in a capacitor. The best way to generate a lot of Joules, is to use lots of voltage and capacitance in capacitors. We are talking on the range of 300+ Volts. The formula to calculate how much joules something has by relating voltage and capacitance is:


J= Joules

V= Voltage

C= Capacitance in Farads

This means that if you had 100 Volts and a 1000uf capacitor, you would have 5 Joules of power, which is not a lot. If you were to boost the voltage to say, 300 Volts and 1000uf capacitor, the power would be 45 Joules. Thats a sinifigant increase in power! That's because voltage is exponental. It is a common practice to increase voltage by sacrificing capacitance. Here is an example:epo elisa kit http://www.cusabio.com/bio1-E-EPO-7-3.html


45= Joules

300= Voltage

0.001=1000uf, but it had to be in a F format so you add a few zeros before it.

That above was a control. We will now decrease the capacitance by half, and increase the voltage by double. We do this by simply adding the capacitors in series, like so: -||--||-

Here is the increase in power


90= Joules

600= Voltage


As you can see, by increasing Voltage by sacrificing half of the capacitance doubles the output power!

for more on coil guns, you can go to wikipedia for more on coilguns.

Ok now for the good stuff!

Most if not all single stage coil guns (multi stage coil guns cost too much so stay out of them) consist of these 4 basic things:

  • Barrel/Coil
  • Capacitor Bank
  • Trigger
  • Charge Circuitry

The Barrel/Coil is made up of many many coils of wire that the discharged capacitors flow through, producing a massive amount of electromagnetic flux, that effectively attacts the ferromagnetic projectile and propelling it through and past the coil.

The Capacitor bank holds the massive amount of energy previously described (Joules). A very cheap source of these capacitors can be found in disposable cameras. The capacitors can have a rating from 80uf+ and 300V+, making these a great source for capacitors.

The Trigger can be anything from a switch to a SCR (Scilicon Controlled Rectifier). A SCR is prefered, because using a mechanical switching method can easily melt the contacts. This is a very common problem, therefore scilicon switching is vastly superior.

The Charge circuitry charges the capacitors, and depending on the milliamp output of the circuitry, it could take anywhere from a few seconds to a few minutes. There are many variables on charging, but the best place to aquire cheap charge circuits (with a low charge rate) is found in disposable cameras.

they are not extremly expensive depending on what you buy and were