Help a total noobie / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Help a total noobie

Move Thread

LAN_403

Shadow

Mon Mar 17 2008, 11:53PM

Registered Member #1398 Joined: Mon Mar 17 2008, 11:44PM
Location:
Posts: 2

I am trying to build a coil gun, but I am completely lost on what I should be doing. I have 2 400v 3600uF capacitors that I plan to use, but other than that I am completely clueless on what I should do.

I am trying to build a single stage coil gun that can fire an object about the diameter of a steel marble. I am not sure if this sounds reasonable for what I have, but if it is not please let me know what I should expect from these capacitors.

Any way, what I am trying to determine is basically, a part list and basic setup information on how to build my coil gun. What specifically leaves me baffled is what kind of power supply I should be looking at, if I should run the capacitors in series or parallel, and how to control the firing of the gun so that the capacitors do not overcharge. However, I am still completely lost on the other aspects of the gun, such as the gauge of wire I should use, and how many wraps is best to use on the pipe.

If someone could give me a rough idea of what I should be doing, along with a part list, I would be most grateful.

Thanks,

Shadow

FireBird

Tue Mar 18 2008, 12:33AM

Registered Member #1104 Joined: Tue Nov 06 2007, 07:38PM
Location: Wisconsin, United States
Posts: 34

For a power supply you could make a simple boot converter like the one here

or if you want to be very cheep and are not worried about charge times, you could use a disposable camera charge circuit. The disposable camera one stops at about 360v so you donâ€™t have to worry about overcharging the caps.

The series or parallel is more what you want out of it. I personally would put them in parallel though.

To fire the coil gun you could use a simple contact switch out of two pieces of metal. For a more efficient trigger you should use an SCR though.

Make sure that your coil form is non-conductive to reduce eddy currents and as for wire gauge and amount of turns you should calculate that based on your cap bank and projectile.

Also this site

is very helpful for a first time coil gun.

rp181

Tue Mar 18 2008, 01:02AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Cylinder projectiles tend to work better than spheres in my guns.
the caps you are saying is more then 500 joules, it takes 16 to kill. You might already know, but be really carefull.
Expierement with a single flash camera first, then go big. SCR would be the best choice for switching, but cheaper is 2 spring loaded plates. When the coil fires, there is strong contraction. Get a strong plastic barrel if you can, if not, use a brass tube that is slotted. Make sure you don't overcharge the caps.

Shadow

Sun Mar 23 2008, 04:40AM

Registered Member #1398 Joined: Mon Mar 17 2008, 11:44PM
Location:
Posts: 2

Thanks for all the help guys. I finally got around to starting on my project today, and as would be expected, I got almost nowhere. I managed to build a nice little gun with that can be triggered with a switch, but for some reason the camera circuit (this is my first attempt after all) was not able to build up more than 96ish volts across the capacitor, and consequently my projectile would not fire. (Note: This was an entirely camera based coil gun, with a straw barrel, a small nail piece for a projectile, and radio shack "magnet wire", and a small switch as a firing mechanism)

Does that sound right, should 96v across a 120uF capacitor be able to fire the projectile? What could have caused such a low voltage? (Worth noting was that my gun circuit did, work, because when I triggered the gun, the voltage across the capacitor dropped to 0)

Another question I have is what do I need to start thinking about to ramp this gun up to a larger projectile. I have some of the materials already (the capacitors and the smallest diameter PVC I could find .5"), but what else should I be looking into getting? I was thinking about using the 5V rail from a external HD PSU as my power source, but I would love to hear a second opinion on that. Also, where would be a good place to start looking for a Boost Converter to fulfill my needs? I would love to be able to just buy one instead of having to build one myself. Another thought that crossed my mind was what kind of amperage should I be expecting these capacitors to discharge if they are charged to 400v, and what kind of wire should I be looking into getting?

David.Lightman

Sun Mar 23 2008, 05:58AM

Registered Member #1327 Joined: Mon Feb 18 2008, 12:13AM
Location: North Ridgeville, Ohio.
Posts: 38

Well, 96v @ 120uf is only 0.55296j, not much potential energy at all. That being said, it should have drawn your projectile into the coil a bit. a tiny bit, but a bit none the less.

To create the voltage I need for my gun I put several large 12vdc batteries together to make my 96vdc. But I put that 96v into 20- 2400uf and 5- 6000uf caps. That gives me 359.42400j ... Enough to launch my 3/8 rod through a cardboard box.

I'm slowly gaining the knowledge to rectify 120vac into 160 vdc to charge my caps. Bought some bridge rectifiers today. I plan on blowing myself up tomorrow... ;)

I would get as much capacitance as you can and ramp up the voltage as you gain the knowledge to do so. Your CG will get better and better.

Good Luck from a fellow Noob!

D.L

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob