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Registered Member #815
Joined: Sun Jun 03 2007, 02:05PM
Location: Denmark
Posts: 1
Hey, I'm new here, so HELLO from Denmark
I've made a couple "coilguns" from disposeable cameras, without calculating anything what so ever, and they are starting to be really BORING! So now I wan't to move on to some more power, and tweak it to maximum. I'm sorry if this is going to be a spoonfeeding topic, but I guess someone hopefully will have mercy, and help me out here. I've tried using Barry's calculators, but I'm confused.
Right, enough rambling, on to business.
Capacitors: 2 * 71V 22000uF I wan't to build a single stage, portable CG, with those 2 capacitors.
Questions:
How do I calculate the right resistance for the coil? Also, lower voltage, higher capacety = thicker, shorter wire for the coil? How do I calculate the size of the thyristor I should use? How would I boost the power, of say 8 AA batt. (12V) or 16 (24V), to 70 V ? Schematics please What size diode should I use for the "freewheel" (think it's called that), and how should it be wired? Parallel to the coil? Also, I've heard that encapsuling( washers and plumbing tube or something) the coil in metal makes it more effecient?
I'm really sorry for all the questions...
There will ofcause be pic's and video's of the progress, and finished gun..
Registered Member #514
Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295
71V is really too low for an efficient gun, I'd series the caps for 140V and 11000µF.
The coil resistance shouldn't be that difficult to calculate, just get a chart with wire gauge vs. resistance/meter and multiply with lenght of wire used. Of course, the resistance of the coil isn't the only limiting factor for the current, the coils inductance matters too. The formulas for calculating the inductance are all over the net...
As for the voltage conversion, a boost converter is what you want. It should be pretty easy to build for this low power level.
And finally about the thyristor and diode: Basically you take the biggest thyristor and diode you can find. Just make sure that their breakdown voltages are above your capacitor banks voltege and that the peak current rating is large enough (bigger the better). You connect the diode in antiparallel with the coil, so that it doesnt conduct when voltage is applied to the coil (cathode to +, anode to -), but short circuits the reverse kickback.
Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
wrote ...
Also, I've heard that encapsuling( washers and plumbing tube or something) the coil in metal makes it more effecient?
It can make a big difference (though sometimes in the wrong direction if eddy currents take over). Have a read of the wiki page (about delta L in particular) and come back if you still have questions.
Higher capacitance means you'll have a longer pulse time if you don't reduce the inductance (coil with fewer and smaller turns). You want the pulse time to be on the same order as the time the projectile takes to pass through the coil.
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70V, 44000uF, Single Coil
