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Guyfrom7up

Mon Jun 04 2007, 02:02AM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

Hi everyone! I had just joined this forum and it seems like everyone has these cool coilguns!

I'm trying to build a CG using a camera flash (cause I really don't get the whole charging the capacitor thing)

I have so far made a coil with 22 gauge (I think) stranded wire. There is about 9 revolutions of wire per layer with 6 layers.

I want to build a powerful coilgun (to shoot a small nail), not a weak one and then work my way up cause I'm kinda short on mmoney

I'm thinking about hooking up six 330 volt, 160uF capacitors in series to a camera board as shown below, srry about the drawing!

Correct me if I'm wrong, but should this setup discharge about 1800 volts into the coil? Would this voltage be enough to make a strong coilgun?

I'm not exactly sure about the switch thing, anyone know of a cheap switch type thing that can handle about 2000 volts?

Please help my diagram, cause I'm not exactly sure where to put the diode (I'm not even sure if I have the capacitor polarity right connecting to the flashboard) because at other places they say having the voltage from the coil going back into the capacitor is bad.

Thanks in advance!

By the way, I'm open to any critism, such as my coil is to short or stuff like that.

Also can anyone point me to a "coilguns for dummies" type of website?

...

Mon Jun 04 2007, 02:42AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

If you use the caps in series you will actually get less stored energy. You are better off paralleling the caps, as your charger will only put out about 300v. Keep in mind that it will now take ~6x as long to charge the caps.

As to the switch, I have seen a wall switch used, or a big fat relay would work. Just about any physically large switch should be fine.

You shouldn't need the diode in your case, they are generally only needed when you have a AC power supply (bare transformer) or when you are using a solid state (SCR/IGBT) switch.

BTW, that coil looks like it is made of abuy 10awg wire, possible even larger.

Also, please be extreemly carefull with those caps. You probably can't kill yourself with them, but they will hurt like crazy if you touch charged bank.

Good resources include the 4hv wiki,

, etc

Simon

Mon Jun 04 2007, 07:04AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

It's not a 2kJ bank or anything but I'm sure you could kill yourself with this bank if you don't treat it with proper respect.

Forget about the 2000V. Stick with ~300V and parallel capacitors.

That kind of wire isn't much good for coilguns, I'm afraid. It could work, it just isn't much good.

Also, your camera flash charger will moan pitifully trying to charge that bank. It will charge it eventually but possibly not to the full voltage with all that leakage from six caps.

Electroholic

Mon Jun 04 2007, 07:31AM

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

NO! the camera circuit will have no problem charging that bank, which is only about 27uf, but it will only reach about 330V.

Guyfrom7up

Mon Jun 04 2007, 07:48PM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

I just checked the gauge and it's 12 gauge. Think it's too thick? I'm checking out the sites that ... gave, thatnks for the replys!

EDIT: So if I were to hook the capacitors up to the camera circuit board in parallel each capacitor would fill up to 300volts? If so, whats the best way of hooking it up to the coil?

EDIT 2: Do you think that this Thyristor is cable of what I want accomplished? (I hope so because it's only like 70 cents)

I don't really get the spec sheet but is this much true?
- You can put through 50-800 volts without it getting all funky

That's all i could find

, the only other info I need is how much voltage is need to turn on the gate

Simon

Tue Jun 05 2007, 04:21AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

Electroholic wrote ...

NO! the camera circuit will have no problem charging that bank, which is only about 27uf, but it will only reach about 330V.

I was referring to the bank with the caps in parallel. I'd assumed we'd given up on the series bank idea (which, I agree, the charger will no trouble charging to ~330V).

Do to practical limitations, each cap leaks a little current, which is in effect like having a bleeder resistor built in. The capacitance itself won't add any load to the charger but the leakage resistance will. Disposable camera chargers are designed on the cheap and will struggle with a load six times what they're designed for.

Looking at the datasheet the 2n6400 can take 50V - nowhere near enough. (If you look, the 800V refers to the 2n6405.) Ignoring that, it can pass 16A. In a very short pulse it'll take more than that. It's possible that might be enough but I think you'll want better ratings there - especially if you're experimenting. If it works at all, after replacing the third SCR you'll soon wish you'd paid that extra bit.

Also, you can't find a trigger voltage because SCRs are not triggered by voltage; they're triggered by current. Check the wiki page on SCRs and elsewhere.

Guyfrom7up

Tue Jun 05 2007, 08:46PM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

thanks!

Here almost a complete drawing of the electrical work of my CG. I would probably add some leds around to tell if it is on or if it is charged. The trigger hits 2 switches, one first (that hooks up the capacitors in series), and the second one which releases the energy into the coil.

I am 99% sure I didn't hook up everything right, especially around the coil area.

If you can tell me whats wrong with the drawing it would be greatly appreciated.

Thanks!

PS I also found this simple coil gun settup, and tell me if I can incorporate this into my design.

[Edit: Image size]

Electroholic

Tue Jun 05 2007, 09:02PM

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

sigh...
If i understand it correctly, you are trying to put all 6 caps in series again, and you circuit will not work.
1 1.5v is not enough to trigger an scr.
2 you will at least need a resister for the trigger, too.
3 as suggest by other members, you should use a parallel circuit, which means connecting every camera charger and caps you have in PARALLEL.

Guyfrom7up

Tue Jun 05 2007, 10:58PM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

THanks for having patiece with me!

I think for starters I'm going to follow an instructable to make a capacitor bank. That in reality should be my first goal.

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