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Multi-Stage coilgun

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hotcrazyfruit

Mon Mar 09 2009, 11:00PM

banned on 5/26/2009
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Iv decided to plan a multistage coil gun, perhaps 5 stages, with 1 262.5 joule capacitor per-stage. (1/2 0.0021F * 500^2) . iv got a bunch of 50 amp SCRs, rated at 610 pulse for 8.3 ms. any idea for switching? im thinking about a photo transistor and an LED, to trigger each succeeding SCR. any ideas? or better ones? thanks xD

KLH

Tue Mar 10 2009, 12:28AM

Registered Member #1819 Joined: Thu Nov 20 2008, 04:05PM
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How do you plan to space your coils? Since you have the same energy source size for every coil, you would need to progressively make larger spaces between the coils to get the most out of them. Even better, arrange the capacitors so that the first stage has the lowest voltage / most capacitance, and the last stage has the highest voltage / lowest capacitance.

Barry

Wed Mar 11 2009, 06:56PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
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Spacing the coils in various ways won't have any effect on each stage's timing. Instead, I recommend building subsequent coils with progressively lower inductance to achieve a shorter LC time constant, which has the desired effect of shorter pulses.

I see nothing wrong about using identical capacitors on every stage, and it has the benefit of allowing a single power supply to charge them simultaneously. Of course, you'd use a series diode to each cap so they charge together but discharge independently.

Cheers, Barry
If a 911 operator has a heart attack, who do they call?

hotcrazyfruit

Thu Mar 12 2009, 01:49AM

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wow, i think i just might do this now. what size of capacitor would i need? would some filter capacitors work from a PC power supply? iv got like 16 of them, so i could put a few in series so they dont blow up xD iv also got 600v x 120A diodes i could use, so they discharge independently. thanks barry :)

Barry

Thu Mar 12 2009, 02:23PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

The 262.5 joule capacitors you mentioned in your first post would work well. Imho, each stage must have at least 10 joules to have a chance of doing anything at all, and preferably 50 joules or more of stored energy.

Connecting capacitors in series vs parallel will have little to do with whether they blow up or not. But you can obtain higher total charged voltage in series compared to parallel.

The 600v @ 120-amp diodes sound good, now if only you had a 600v 120-amp power supply!

Me too, I want a 72 KW power supply, too! Anyway, you'll probably end up charging at a rate of a few amps at most; the 120-amp diodes would work fine, but a smaller cheaper 10- or 5- or even 1-amp diode would probably work fine too.

Cheers, Barry
Has The Large Hadron Collider Destroyed The World Yet?

hotcrazyfruit

Thu Mar 12 2009, 03:31PM

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yea, when i said about connecting in seris, i meant the filter capacitors bewteen gates, but i was misleading myself to thinking i had to make them rated for 400v instead of like 9 for the gates. it is a delay between gates i need. and thanks for the comments. o and btw, my freidn and i are making an electroloyis apparatus, with a 240 * 60 amp power supply. u do the math, since i dont have a calculator xD once we step it down to 20 volts, we will have somethign like 480 amps. xD but thats off topic now lol.
thanks

hotcrazyfruit

Thu Mar 12 2009, 03:34PM

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Camel

Fri Mar 13 2009, 04:22AM

Registered Member #1694 Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
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hotcrazyfruit wrote ...

Iv decided to plan a multistage coil gun, perhaps 5 stages, with 1 262.5 joule capacitor per-stage. (1/2 0.0021F * 500^2) . iv got a bunch of 50 amp SCRs, rated at 610 pulse for 8.3 ms. any idea for switching? im thinking about a photo transistor and an LED, to trigger each succeeding SCR. any ideas? or better ones? thanks xD

The multistage gun I'm working on has exactly that and so far its working very well. Want a schematic?

hotcrazyfruit

Fri Mar 13 2009, 08:05PM

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i would love one :), im in florida right now and i have to type up some stuff on it for the science fair. again i would love the scematic xD. thanks

El_Roberto

Fri Mar 13 2009, 09:05PM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
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Yea before I left for uni I was building a 2kj 6 stage coilgun and while I never made more than one stage (I couldn't afford it after paying uni fees) it could still shoot through about three cans (~300j source, 2/3 charged). So I think ~250j per stage works great, but your scr's wont be powerfull enough, my last stage (had I completed it) would have a peak current of around 4500amps. Of course you could use a large bore size to reduce projectile speed and then the longer pulse would have lower current.

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