Final Coil gun post (hopefully hehe :))

[daviddoria]

Ok here's the new schematic.
(the drawing omits a couple of the switches)

http://www.bandtank.com/david/coilgun.wmf


There is a switch and a lightbulb in series between the wall outlet and the DC rectifier (to establish a load). Then out of the rectifier there is another switch to close to start charging the capacitor. then to discharge the capacitor over the coil i have a momentary switch and the coil in parallel.

this is basically the same idea it just now doesn't break my house breaker every other time

however... i also rewrapped my coil. i used 14 AWG 2 layers Left to right (2 leads) then left to right again (another 2 leads) these 4 leads are what are connected to the capacitor all in parallel.

the problem is that the nail only goes to the end of the barrel (8 inches) where it used to go several feet before the new coil wrapping.

whats up with that??

if we get this answered i'll stop babbling about this silly project

 

[Prof.Insane]

Maybe coil has too many turns ?

It sounds like the capacitor still has energy left in it when the nail nears the end of the tube. Does the nail shoot out of the end of the coil a bit and then get sucked back in ? If that's so, the coil needs to eat more energy quicker?(fewer turns?) I'm no expert on this though!

-Chris

 

[daviddoria]

so 1 or 2 layers is ok? or do i need several?

 

[Prof.Insane]

Fewer turns of thicker wire ?

No. If the nail gets sucked back into the coil you probably need fewer turns of thicker wire. But if the nail just shoots a few centimetres out of the coil then I would try a bigger capacitor. 1uf does seem small. But I've never built a coilgun. I'm just guessing from things I've read

-Chris

 

[daviddoria]

i am using 10,000uF.....

 

[Phasor]

I'm guessing that the lightbulb is your problem - it acts as a current limiter - which is fine, in terms of eliminating the breaker trip. However, I suspect that you actually NEED the extra current.

I don't know much about coil guns, but seeing that the projectile is driven by magnetic flux, and flux is proportional to current - then you have effectively reduced the available flux, and hence reduced the driving force on the projectile, by inserting the light bulb.

My idea is to use a stepdown transformer - from 120V to about 12V - because voltage isn't important, but current is. By stepping down the voltage 10x, you can step up the current 10x. BTW, it needs to be a pretty hefty transformer, probably about 100A on the secondary.

 

[Dave the Embalmer]

Voltage is very important. I = V/R. More voltage = more current. 'Nuff said. Lets say the coil has a resistance of 100mOhms. For current, that's 120/.1=1200A. If you used 12V, you get a much less impressive 120A.

Secondly, a cannot stress this enough: Charge up the capacitor, and DISCONNECT IT FROM EVERYTHING EXCEPT THE COIL. When firing the coil gun, nothing should be hooked up to the wall. However, the lightbulb is a good idea when charging the capacitors, as the capacitors probably have very low ESR, and would likely try to draw amps within the four or 5 digits. Even if it will only be drawing this for a few micro or milliseconds, it might be enough to trip a breaker. But if you just leave everything plugged in, well, you may as well just short your outlets out.


My advice to making fixing the coil is to add another layer, same gauge. Make sure you're hooking all the coils up in parallel. It sounds like there is too much resistance, which will lead to a slower capacitor disharge. 1 more layer will cut the resistance down, increasing discharge rate, and hopefully preventing any suction backward after the projectile goes past the center of the coil.

 

[Phasor]

I don't know much about coil guns

Perhaps I am incredibly wrong about all this

 

[mammanoti]

I have to ask; are you in the habit of scanning in your economics notes? Check out your link and remove everything past your name.

 

[daviddoria]

so... what do i care if people see that stuff?

and just fyi it was because my friend was absent a few days.

 

[compute_a_nerd]

what is this about e-con notes?
thanks
Chris

 

[mattg2k4]

I'm not sure how to improve your coil, but here is how I built my prototype coil.

I have a 40v transformer hooked up to a rectifier and 3 4700uf caps in parallel, which so far is pretty much the same as yours. I actually put these caps together for the purpose of making some nice big sparks, but because I've always been interested in coil guns, I grabbed a roll or 18 (or so) gauge wire I had laying around, and hooked it up to the caps with a momentary switch. To fire it, I unplug the transformer and hit the switch. It shoots a small precision screwdriver roughly 4 inches long (my favorite projectile) about 4 feet across from 2 feet up. I've found that placing the projectile nearer or further from the coil can have significant effect on how far it is shot.

So I think the big difference between our guns is the coil. It's simply a roll of 18 guage hook up wire. It's probably about 35 feet, minus a few feet I've used. You could try making your coil larger, see if that works. It just happened that this was the easiest coil to use, but it works pretty well.

Here is a picture of the coil I used:
**broken link removed**[/img]

 

[kinjalgp]

The coil look preety big and the field must be strong too. But one thing I would like to advise you is never overlap the turns of the coil as it is seen in the photograph. This causes the magnetic lines of forces generated by each turn to cancel one another and it reduces the net strength of the field. Avoid overlapping as far as possible.