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I am building a new coil gun and need help with getting parts.

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LAN_403

Arcstarter

Tue Jun 03 2008, 03:43AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Ok so i need some good caps and an scr and ideas for a coil. I am considering these:

And:

The first one is 453 joules at 360 volts, which i would use because i only need to make a voltage tripler.

The second is 1904 joules at 480 volts which would only require a voltage quadrupler.

I am going for a coil gun that can shoot a nail hard enough to maybe penetrate an apple or potato, or even more. I will probably use it for a steel plate shooter(yea, whatever you call them, i suppose it would be a thompson gun)or just washer shooter.

Turkey9

Tue Jun 03 2008, 03:59AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

with that much energy you could do a lot more than just shoot through a potato. So with even the smaller cap bank you could reach your goal with a relatively low effeciency single stage gun. And for a thompson gun you need to have a non magnetic projectile because it all works on eddy currents to repel it.

Arcstarter

Tue Jun 03 2008, 03:24PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Thanks to teslacoolguy, i am going to get 2 3900uf capacitors that i will charge to 360 volts. that is 250joules each. I guess i will do some can crushing and wire exploding also. I also have a place to buy an scr and a good stud diode.

I bought the capacitors, as well as 5 pounds of other various capacitors. I am going to put the caps in series(thank you teslacoolguy) and charge them up to around 800volts(their peak voltage). I need a power source to charge them. I was thinking about a simple circuit like in a camera, just use a primary winding and feedback an have that run a transistor and the secondary will just be whatever it takes for full voltage. I could also try a boost converter but i don't have an inductance meter or any other way to measure inductance, so the only way that will work is if someone can tell me how to make one with a ferrite toroid, about 1 1/2 to 2 inches in diameter. I think i am going to go with simple feedback circuit because i have a ferrite transformer perfect for it.

Shaun

Tue Jun 03 2008, 07:00PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

You are going to have a difficult time can crushing with these capacitors; they don't discharge fast enough and don't handle inductive loads very well. And good luck finding an SCR to handle that current. You should be fine exploding wire tho.

Also be careful with wiring all capacitors in series; if they arent all exactly identical some will reach higher voltages than other. YOu will need balancing resistors.

Arcstarter

Tue Jun 03 2008, 07:06PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Shaun wrote ...

You are going to have a difficult time can crushing with these capacitors; they don't discharge fast enough and don't handle inductive loads very well. And good luck finding an SCR to handle that current. You should be fine exploding wire tho.

Also be careful with wiring all capacitors in series; if they arent all exactly identical some will reach higher voltages than other. YOu will need balancing resistors.

Great.... Oh well. Can you give me an idea of what wattage?

uzzors2k

Tue Jun 03 2008, 09:43PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Wattage will depend on their resistance and capacitor voltage. Use Ohm's law to find out how much power they will dissipate, and add some overhead. I've heard their resistance should be small enough to let 10x the average leakage current of each capacitor pass in order for them to balance the capacitors properly. Leakage current will probably be in the datasheet.

w00t! post 700!

Arcstarter

Tue Jun 03 2008, 11:16PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Uzzors wrote ...

Wattage will depend on their resistance and capacitor voltage. Use Ohm's law to find out how much power they will dissipate, and add some overhead. I've heard their resistance should be small enough to let 10x the average leakage current of each capacitor pass in order for them to balance the capacitors properly. Leakage current will probably be in the datasheet.

w00t! post 700!

Oops i meant current.

Weston

Wed Jun 04 2008, 12:20AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Like said earlier it should be 10X leakage current at peak voltage

Arcstarter

Wed Jun 04 2008, 02:48AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Weston wrote ...

Like said earlier it should be 10X leakage current at peak voltage

Maybe i should not get into coilguns, 'casue i don't really get leakage current. Or know what it is at all....

Anyway, I also need some bleeder/balancer resistors and a charger. I was thinking about using a boost converter or better yet a simple single transistor circuit like in a camera,running from either 12 or 24 volts and a homemade transformer. I have decided on the caps i am getting. They are mallory 3900uf 400 volt capacitors. They are going to be paralleled for a total of about 600 joules. I also need to know the approximate discharge current as i don't have a scope or anything like that, just multimeters. If you can give me the calculated current, not a formula because i am not good at math.

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