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Coil construciton: 80amp through 30aw wire?

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LAN_403

PlayNice

Thu Dec 13 2012, 02:52AM

Registered Member #8032 Joined: Tue Nov 13 2012, 01:22AM
Location: Chicagoland USA
Posts: 33

Yea I could do that too, use one higher inductance coil then use low inductance coils on all the rest. I was thinking compressed air because modifying a bb gun will be easy and it will give the general shape for the whole gun.

Yandersen

Thu Dec 13 2012, 04:40AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

IGBT for reluctance coilgun?!?!
The push-force projectile experiences is proportional to the square of the current and speed of it's rize (which is proportional to the frequency of oscillations). Reluctance coilguns are purely LC oscillators, which are easily build on non-polar caps and bi-directional thyristors. For a little current IGBT can handle and a single pulse you will not be able to push a projectile out of the coil. But we will see, good luck. ;)

PlayNice

Thu Dec 13 2012, 05:00AM

Registered Member #8032 Joined: Tue Nov 13 2012, 01:22AM
Location: Chicagoland USA
Posts: 33

IGBT can handle 60amps and 160amps if pulses. If not IGBT then what would you use for switching? I don't have to use IGBTs I just though it was a good idea because they can produce a nice square wave. I'd love to hear your input

Yandersen

Thu Dec 13 2012, 05:34AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

"...easily build on non-polar caps and bi-directional thyristors." - who did just said that right above your post, huh?.. :)

klugesmith

Thu Dec 13 2012, 05:36AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

supak1 wrote ...

Yea I could do that too, use one higher inductance coil then use low inductance coils on all the rest. I was thinking compressed air because modifying a bb gun will be easy and it will give the general shape for the whole gun.

Uh, as maxwell said, why not use the air gun by itself and skip the coil?
IMHO, a pneumatic injector for a coilgun is like using a blowtorch to light a match, except perhaps for seriously big and expensive CG's.

80 amps in your 0.4 ohms of 30AWG wire represents a power of 2560 watts, not counting thermal increase in R. If you limit the pulse duration to 1 ms, that's 2.56 joules of heat to the coil. My unreviewed calculation says the wire temperature rise would be between 10 and 15 degrees C.

So at 10% efficiency, you would add only 1/4 J of energy to the projectile.

For reference, the UK allows unlicenced air guns up to muzzle energy of 12 ft-lbf (16 J).
What's the energy of your BB gun? Is it one of those Airsoft toys?
If you have compressed air, please consider:
A projectile area of 1 cm^2, at only 120 psig (8.2 bar), receives 83 newtons of force.
In 1 meter that could impart 83 joules of kinetic energy.

[edit]

Maxwell wrote ...
If you're looking down that road, you realistically should switch out from HV completely.
The major benefit of these CG's is that they are damn close to being silent ...,

Same goes for air guns designed for chamber pressure to match atmospheric pressure when projectile leaves the muzzle. Tuning for efficiency = tuning for quietness, as in my old CO2 mortar that used a pneumatically exploded soda bottle as propellant charge. Impressively quiet as it lofted a 16.5 lb concrete piston for more than 5 seconds. By scale & stopwatch, muzzle energy was > 2000 J.

Yandersen

Thu Dec 13 2012, 05:39AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

To make bi-dir thyristor conducting, wind two coils around a little ferrite ring transformer: one coil connects between the thyristor's cathode and gate, and on a second coil oscillating wave goes. While vibrating, thyristor will be constantly triggered (in a conductive state).

Turkey9

Thu Dec 13 2012, 07:07AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

IGBTs can be used very effectively if you don't want to use the LC time constant to determine the pulse length.

I would strongly advise against using such thin wire. You won't notice a difference in using a single layer as compared to two or three. Thicker wire will make the entire coilgun much more durable. You don't want to spend a lot of time building something only to have it break after a couple shots.

PlayNice

Thu Dec 13 2012, 07:34AM

Registered Member #8032 Joined: Tue Nov 13 2012, 01:22AM
Location: Chicagoland USA
Posts: 33

But whats the point of having the thyristor triggered by the oscillation? Shouldn't my opto-switch be triggering my thyristor so I can have the timing right and not have suck-back?

Yandersen

Thu Dec 13 2012, 11:40AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

There is no suckback in a reluctance coilgun - it pushes the projectile away from the coil, wherever it is, but with distance increased force is weakening.

PlayNice

Thu Dec 13 2012, 08:20PM

Registered Member #8032 Joined: Tue Nov 13 2012, 01:22AM
Location: Chicagoland USA
Posts: 33

The one that pushed the projectile is induction coilgun, I though reluctance coilgun pulls the projectile like this:

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