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My 5-minute coilgun

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Edi

Sat Mar 29 2008, 05:49PM

Registered Member #1414 Joined: Sat Mar 29 2008, 04:49PM
Location: Krk, Croatia
Posts: 6

Greetings from sunny Croatia.

I'm reading your site for a quite time, it's really great, and I found a bunch of information about coilguns, so I made one.
It is made of mostly junk parts from old amplifiers.(sorry if I misspelled something).
Capacitors are 22000uF 40 V and 15000uF 25V in series, about 20J with 68 V charge (4 trafos in series with rectifiers and caps etc.).
Coil is made from relay wire, I think 0,2mm, about 50 turns on 2.5mm diameter pen tube.
It is switched with BT152 600R SCR (20 A, 200A peak), and a projectile is steel magnet 1 cm length, 2.5 mm dia.
Well, results are very crappy

Magnet flies about 1m, slow as turtle or something like that.
I attached video so see.
Gentlmen, comment please, and tell me how can I do improvements.

One more thing:
Marko, prijatelju, gdje nabavljaÅ¡ velike kondenzatore (ako nabavljaÅ¡), ja nemogu naÄ‡i niÅ¡ta i nigdje.

Sorry, too big video, posting new.
]coilgun.wmv[/file]

[Edit: Double post]

ramses

Sat Mar 29 2008, 06:15PM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

welcome!

you should try to use this: http://www.gausspistol.com/Simulator.html
it is really helpful, there are some basic instructions on that page.

it may help to describe the coil and barrel more ex how many layers in the coil, how thick the barrel is, etc.
you are probably make the coil longer, but i can't say for sure. a projectile with a greater diameter would probably be more efficient.

ramses

ps. if anyone wants to let me know how to link properly, please feel free...

Edi

Sat Mar 29 2008, 06:40PM

Registered Member #1414 Joined: Sat Mar 29 2008, 04:49PM
Location: Krk, Croatia
Posts: 6

Thank you, sir. Very useful site.

The very problem in my town (maybe even country) is no big capacitors - biggest I see in shop is 470uF 400V, and it's awful expensive. From other countries like Germany taxes are about 2x more expensive than capacitors .Well, I'll try find some in old photo flashes or something like that. 'till then I'll try to incerase effectivity of this crap.

Bjørn

Sat Mar 29 2008, 06:58PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Change the starting position of the projectile and see if that helps. It is likely that your pulse lasts too long.

When the capacitors are so different it is rarely a good idea to put them in series.

Edi

Sat Mar 29 2008, 07:09PM

Registered Member #1414 Joined: Sat Mar 29 2008, 04:49PM
Location: Krk, Croatia
Posts: 6

Yeah, I put it before in parallel, but projectile stuck in middle (the pulse is too long, I thought...) then I put it in series, and all worked (I won't say fine because it isn't). I'll try change position, thanks BjÃ¸rn.

ramses

Sun Mar 30 2008, 01:42AM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

since caps are so hard to find where you live, be darn sure you don't put too much voltage into either of your caps! also, you may want to put a diode in anti-parallel with your coil to keep from damaging your SCR, or your precious capacitors!

camera flashes are an OK source, but they are around 330v. I have personally taken a discharge between 2 fingers, and can tell you that it HURTS... A LOT. so play save, and expect to use several camera flashes worth of capacitors to get around the 20j you have now.

your SCR looks to be able to handle this, but don't short the capacitor bank and expect it to like it!

and I just thought of another way to possibly improve performance. external iron:

seriously people, how do you make that nice link arrow thing?!

ramses

[Edit: By entering the complete URL without any bbcode.]

Bjørn

Sun Mar 30 2008, 02:08AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

At this point the efficiency is pretty much zero so the energy in the capacitors does not figure into it, it is all about increasing the efficiency to get as much energy as possible into the projectile.

If we say that the projectile has a weight of 0.4 g and we have a photocapacitor of about 6 joules. Then will get a speed of about 55 m/s at 10% efficiency, a lot faster than a turtle.

Electroholic

Sun Mar 30 2008, 03:57AM

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

I think you are over volting your 25V cap, you can't hook uf caps with different voltage and capacitance rating and think it will stand up to the sum of voltage rating of the two caps. The smaller cap is going to see a lot more voltage than the big one.

Edi

Sun Mar 30 2008, 09:48AM

Registered Member #1414 Joined: Sat Mar 29 2008, 04:49PM
Location: Krk, Croatia
Posts: 6

Wow, alot of info. Thanks people

External iron, I think I can get from trafos (maybe cheaper from old iron warehouse...?).
Well, caps are still alive, the smaller cap has good surge voltage (I think 40V) , but you never know what will decide cap (boom or not)

Changing position of projectile wasn't made big effect

, never mind

Thanks very much people, I'm going to hunt some caps now.

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