# Coilgun help

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#### Roen Hayden

Joined Sep 10, 2007
22
Hello this is my first post, i found this website from reading the book electronics for dummies.

I have been working on the idea of a Coilgun for weeks now and i think i have a general idea of how they work i just want to run my idea buy this community. Basically i plan on using a camera circuit to charge the caps.

Now if i have four caps all of them are the same and lets say hold 330v will one camera circuit fully charge them, for a out put of 1320v? the camera circuit will run of ether a 1 1.5v or 2 of them not sure yet. And what wire should i use to wrap around the barrel? I'm sure i'm still missing something if so please do tell.

thanks

#### hgmjr

Joined Jan 28, 2005
9,029
The Internet is full of sites with information on this topic. I googled coilguns and there were a number of hits that would be worth exploring.

Here is just one of the websites with info about coilgun.

hgmjr

#### Roen Hayden

Joined Sep 10, 2007
22
The Internet is full of sites with information on this topic. I googled coilguns and there were a number of hits that would be worth exploring.

Here is just one of the websites with info about coilgun.

hgmjr
Yes i have seen that site many times before. but i was hoping to get the other question answered directly. That one has stopped me from building the Coilgun. But one of my questions were answered by that site i have to use magnetic wire.

#### thingmaker3

Joined May 16, 2005
5,084

#### andy73

Joined Sep 26, 2007
10
Hi Roen,

coilguns are fun, i am building one at the mo, 2 stages, optical gate switches, 475 joules with 16 joules out so far, any way back to your question. if you put the photoflash caps in para then you will increase the capacity eg:

1) 120uf + 120uf + 120uf = 360uf, the voltage stays the same = 300 - 320v (you never get 330v as caps never really get full)

2) yes a single flash circuit will do the job but will take forever to charge the cap bank up, so you can para the charge circuits to make a faster charger, take the + and - out puts from one circuit and connect them to the + / - of the next, each charger gets a battery and off you go, i have added a quick drawing of the above.

parallel circuits = Voltage stays the same capacitance gose up = longer pulse time
series circuits = voltage gose up capacitance gose down, then caps go BANG!! no pulse, anyway its easier to make a para cap bank. the more you play with CG's you will realize that its pulse time and joules in + coil dimentions and not pure voltage that makes them faster. a well designed 300v CG with 200 - 1000 joules can hit 100m/s+ speeds no problems. but a bad one with 1000v and 2000 joules will get the dreded "suckback" effect and only fire at 30m/s

now the coil is a fun part, the guage of wire, voltage, coil dimemtions + pulse duration all factor in a efective CG.

http://www.coilgun.ru/

go to this site and look at Barry Hansen's and Donnie James's gun sites there is a ton of info you will need, but a simple coilgun is fun and easy. Donnies is fantastic for charging circuits, 4 x 470uf caps in 2.8 seconds!!! with a slight alteration from me is now hitting 16 x 470uf caps in 3.85 seconds. anyway back to your gun.

when you advance to bigger guns with more power then you will want a SCR switch (details on drawing) and a meaty charging circuit, + some big caps,

I have written an excel program that works out all the different factors for designing a good CG, if you let me know what caps you have (uf + V + how many) your coil dimentions, projectile weight dimamter + lenght i can work out estimated amps flyback for you, saves SCR's

my first CG from flash circuits was made of 8 chargers in para charging 4 + 80uf caps @ 315volts,

good luck and have fun, oh and if you are going to make a CG get ready to shock yourself a few times

cheers

#### andy73

Joined Sep 26, 2007
10
Doh................forgot to attach the attachment!!!

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#### Roen Hayden

Joined Sep 10, 2007
22
If I have 4 caps in parallel and each cap can hold 330v what will be the output of the caps? 330v or 1320v. I ask because I’m still not getting the idea... I have read that Capacitors connected in parallel will add their capacitance together. So that why I think it adds up to 1320v but I have been told otherwise by other sauces so I’m not sure which is right. I do know that the camera circuit increase the voltage output by using a step up transformer from the camera.

#### SgtWookie

Joined Jul 17, 2007
22,210

Capacitors in parallel are additive for current. Capacitors in series are additive for voltage.

Cap values in series are calculated like resistors in parallel.
Cap values in parallel are calculated like resistors in series.
(This seems odd, but is true.)

Camera flash driver circuits step up voltage via a boost circuit. You won't get near enough power to drive a railgun.

Don't even try such experiments unless you have become very familiar with how circuits respond when dealing with low voltage, low current projects.

The person you kill might be yourself.

#### Roen Hayden

Joined Sep 10, 2007
22

Capacitors in parallel are additive for current. Capacitors in series are additive for voltage.

Cap values in series are calculated like resistors in parallel.
Cap values in parallel are calculated like resistors in series.
(This seems odd, but is true.)

Camera flash driver circuits step up voltage via a boost circuit. You won't get near enough power to drive a railgun.

Don't even try such experiments unless you have become very familiar with how circuits respond when dealing with low voltage, low current projects.

The person you kill might be yourself.

so if i have 4 caps in para each one can hold 330v what willl be the output of the four? yea i know lol back from the dead..

#### scubasteve_911

Joined Dec 27, 2007
1,203
You'll have ~300-315V across the capacitors.. Just don't kill yourself, that's a ton of energy to discharge.

If you wanna check out some coilgun simulation, there is free software for it and an example. http://femm.foster-miller.net/wiki/Examples

You'll probably need to tradeoff voltage and capacitance when you get into it, since they have a huge effect on how your coilgun will perform. Higher voltage equals faster current discharge into the inductance (coil), but less sustained current than a similar bank (ie. parallel).

Steve

#### Roen Hayden

Joined Sep 10, 2007
22
You'll have ~300-315V across the capacitors.. Just don't kill yourself, that's a ton of energy to discharge.

If you wanna check out some coilgun simulation, there is free software for it and an example. http://femm.foster-miller.net/wiki/Examples

You'll probably need to tradeoff voltage and capacitance when you get into it, since they have a huge effect on how your coilgun will perform. Higher voltage equals faster current discharge into the inductance (coil), but less sustained current than a similar bank (ie. parallel).

Steve

then if all 4 only goes to 300-315V across all the caps why don't i only just use one?

#### thingmaker3

Joined May 16, 2005
5,084
Volts aren't what kicks the nail out of the tube. Joules are. Four caps at a given voltage will yield four times as many Joules as one cap at the same voltage.

#### kubeek

Joined Sep 20, 2005
5,718
Why do people use such high voltage for coilguns? Isn´t easier to use lower voltage like 50-100V and higher currents?
It wouldn´t be that dangerous, and big caps for lower voltage are cheaper than high voltage caps.

#### thingmaker3

Joined May 16, 2005
5,084
It's that formula, again. Double your voltage, and you quadruple your energy. If you want to use 1/10 the voltage, you'll need 100x the capacitors.

#### Caveman

Joined Apr 15, 2008
471
kubeek,

The goal of a coilgun is to create a very fast current pulse. Since it is an inductor, it resists fast current pulses. An inductor's current "charge" rate is related to voltage. More voltage = more current in the same time.

Another effect is the back emf that the transfer of energy causes. Effectively, the mechanical work being done by the coilgun causes some of the voltage on the coil to effectively not be on the inductor, so it doesn't help to increase the current. You have to add voltage.

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