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Help with first coil gun

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LAN_403

NoooobToHV

Sat Apr 05 2008, 08:59PM

Registered Member #1356 Joined: Tue Feb 26 2008, 12:02AM
Location:
Posts: 6

Hey I just made a photo cap coil gun. It uses three 330V 120uF caps in parallel, no diodes no SCRs nothing like that. The only thing is i can not get the Caps to discharge. The coil is 100 Turns in a little less than a a inch and 22 gauge magnet wire. Any one know why the caps wont discharge?
All help is appreated
Thanks

Gnarly

rp181

Sat Apr 05 2008, 10:40PM

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

First of 100 turns is way to much (im fairly sure). Low number of windings with thicker wire is generally better.

Check your connections over again, and if u have one, use a voltmeter to see if the caps are even charging. When you fire and nothing happens but cap was discharged, you probably have a bad projectile placement, or its to heavy for your power.

Electroholic

Sun Apr 06 2008, 12:09AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

100turns is fine. but you would probably wnat to strip the insulation off the magnet wires.

EDY19

Sun Apr 06 2008, 12:56AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

How are you charging the capacitors? How are you triggering them to discharge into the coil? Getting the capacitors to discharge should be a simple task of putting something conductive across the terminals, so a little description of your setup would be very helpful in figuring out your problem.

FireBird

Sun Apr 06 2008, 01:04AM

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

Without some more information or a picture or something it will be hard to help. You should make sure your caps are even charging. If you have the coil connected directly to the caps, it will not charge. You need some form of a switch, even if it is as simple as touching two wires together.

Lakeowner

Sun Apr 06 2008, 10:13AM

Registered Member #1370 Joined: Mon Mar 03 2008, 09:01AM
Location: Finland
Posts: 56

After you have necessary system for charging, think how to protect your caps. Get at least a diode across the cap bank. It's strongly recommended because coil (inductor) will otherwise charge your bank to negative voltage. Electrolytic caps won't like that.

NoooobToHV

Mon Apr 07 2008, 04:25PM

Registered Member #1356 Joined: Tue Feb 26 2008, 12:02AM
Location:
Posts: 6

I just took a picture ill get it up soon ... as for the caps i know theyre charging because i can decharge them with a pair of pylers and it makes a nice and big bang with a light show. As for charging them i rigged the charger from the camara to charge them. Finally i do have a switch and i have a 220 ohm resistor to increase the current ... The coil is enameled magent wire though ... could it not be firing because i havent shaved enough of the enamel off. as for the comment that the person said 100 turns was to much isnt the Resistance of the accual coil negiable?

Edit: I have no idea why i said the resistor to increase the current ... what i ment to say was that the resistor is there to because me and my friend were looking at it and we thoguht i wasnt firing because there wasnt a large enough potential difffernce ... secondly the switch isnt rated for ne thing above 10 A so we tried to decrease the amperage so it wouldnt blow the switch

NoooobToHV

Mon Apr 07 2008, 04:40PM

Registered Member #1356 Joined: Tue Feb 26 2008, 12:02AM
Location:
Posts: 6

Heres a picture

Lakeowner

Mon Apr 07 2008, 05:40PM

Registered Member #1370 Joined: Mon Mar 03 2008, 09:01AM
Location: Finland
Posts: 56

Your caps are quite small. Don't expect too much energy :). Also, don't use any kind of resistor between cap and shooting coil. The whole point of coilgun is to discharge cap through an inductor _fast_. Even little resistance (say 10 ohms) decrease performance well. When dealing with low voltages, minimizing resistances becomes extremely important.

Andyman

Mon Apr 07 2008, 07:22PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

I'm a little surprised that the resistor hasn't exploded.

All its doing is annihilating your efficiency. There might as well not even be a coil there. The resistor is taking the current and turning it from a potentially high current millisecond pulse into a low current, slow bleed off of the caps.
Bottom line - get that resistor outta there, pronto! Or at least move it before the capacitors to act as a charging resistor.
Also, try making a mechanical switch instead. It will handle alot more current. For my first switch, I simply got a thick copper wire (like 14 awg or something) and pounded it relatively flat. Then I used a soldering iron to solder on a lead from it, and at the same time melt it to a piece of acrylic (actually, it was a CD). For the other contact, I used one of the laminations from a small transformer with the black coating scraped off. I also melted that to the CD. Heres a picture of it.

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