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Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
The circuit will function just fine without the control circuitry.
I can't imagine what would make them explode like that. Did you change anything other than disconnecting the diodes and switching out the battery? Maybe check your wiring, perhaps the comparator is mistakenly wired to or contacting one of the high voltage parts, and the problem only became apparent after you were able to generate the high voltages.
Registered Member #3785
Joined: Sat Mar 26 2011, 03:37PM
Location: Surrey, UK
Posts: 16
Well, I vaguely know what went wrong now :) the cheap stripboard from maplins couldnt take the 10+ amps the drill battery pushed through it, and melted, leaving one MOSFET on it's lonesome, which frazzled the MOSFET so that it conducts across all 3 terminals. Then, the primary melted because of this MOSFET frazzling.
In conclusion, I'm going to re-wire the whole driver circuit floating, with some beefy 16awg wire, order some new mosfets, and hopefully add the voltage detection circuit at a later point :) ah electronics never fails to infuriate me :P
Registered Member #3785
Joined: Sat Mar 26 2011, 03:37PM
Location: Surrey, UK
Posts: 16
Hi again all. I'm going to refrain from moving this thread to the project forum until I machine up an enclosure for the gun an complete tuning, but as of yesterday my gun is fully functional.
Charging time for a 10mF cap bank to 400 volt was in the region of 10 seconds. Power was supplied by an 18V high discharge powertool battery. Using a coil of 16AWG enamelled wire, 5cm long, 10 layers thick I flung a projectile 50mm long and 12mm in diameter across my garden.
I'm suffering a lot from suckback, and had a fair few backwards launches! I presume I was a tad overzealous with my coil, and I assume removing turns to decrease inductance would shorten my pulse considerably? Beyond that, I just need to experiment with projectile length, (Barry's site recommended a ratio of in the region of 2/3 projectile to coil?) and also placement relative to coil. At the moment I'm using a bolt action system, but ideally I would love for the gun to become fully magazine fed and semi auto :)
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Nice work and good video! The extra 12V happens on my coilgun too. I think it's caused by dielectric absorption- when the capacitor discharges, some of the energy is lost internally as heat in the dielectric fluid, then the heat energy recharges the capacitors a bit.
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Coilgun Project Help
