Coil Driver/launcher circuit
Posted on Jun 10, 2012 11364
Under: Safety Circuits
This is a fun and non-dangeros project for those people who like to throw projectiles magnetically. It simply works by placing a ferromagnetic projectile at one end of a coil and pulsing some power in it. The trick is to switch off power when the projectile is at the middle of the coil, there are some ways to do it but it isn't important now. The second trick is to use a coil as close as possible to projectile to waximize coupling and the third to avoid saturation, that means keeping the current not to high. I've been messing with coil launchers for a year. The first model was a straw with some wire wrapped on it and an electrolityc capacitor (200V) pulsed in it. Lots of sparks and metal flying but was able to shoot a nail accross my room.
Click here to download the full size of the above Circuit.
I started esperimentation wrapping wire on glass and using more litycs charged by mains power, very bulky and disappointing (100J of energy where only able to blast through 2 sheets). After holydays I started more mature experimentation employing SCRs (solid state switching) photoflash electrolytics and optical sensors, and built a bi-coil launcher (2 stages), complicated but poweful ( blasted through a can) but the timing is critical, so transient simulations were a must (and a L-C-R meter). The next launcher will be mosfet-switched with 3 coils and optical sensors, but i don't have the funds/parts yet to build such an expensive launcher, but already designed plans and models. For now i decided to build a small funny coil launcher using one scr and coil on glass. Using my LCR meter and multisim simulator i designed it for max efficiency. For first you need some disposable camera flashes, so try to search at your local photo shop. You need 4 of more of them. Desolder the caps and collect them. They have ratings of 330V 120-160uF and can survive pulses up to 300A (each), or even dead shorts (but don't do it because it is quite a bang). Paralleling them reduces the ESR (internal resistance) and ESL and highers peak current capability. I used 4 of them and my coil launcher has a pulse current of 400A (about 100A for cap). The more caps , the more energy Concerning the charging circuit, use the largest you got, and try...