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Registered Member #6188
Joined: Wed Aug 15 2012, 08:34AM
Location:
Posts: 23
Ok, im building a coilgun, right now i finished winding the coil and am testing a single capacitor on the coil, im using one of the 450v 560uF capacitors to power it, carefully charging off the improvised boost converter made from a single stage voltage doubler and a $6 chinese 12v inverter, which gets me 500v at 150W i think, im not sure, but it does charge the capacitor in 15 seconds, i dont really care though, its just an improvisation, ill build a dedicated boost converter.
So, here it is, the coil. its made from 1mm wire, 40mm long, and has 7 layers, not by choice, i just happened to run out of wire, i would have added more given i eventually hope to do a full 5600uF @450vdc through it, or at least half if thats enough, that way i can have a dual bank.
heres a pic
just testing it out, it seems pretty strong, not liking all the sparks shooting out from every contact though. the ammunition for now, is a brass coated screw with the head removed, its fairly light and probably would pass through paper at close range, or peirce it at any other distance. though it doesnt yet utilize as much juice as the last coilgun i made which ultimately failed from parts wearing out, its putting out much more power, as in higher efficiency, because of the neater coil winding. i have yet to calculate the joule output which is something i wanted to ask for help about.
tomorrow im going to buy some copper rails at the hobby shop and gradually add capacitors to make up a bank, testing the power with each additional capacitor. If im overpowering it what should be happening? hot wires? hot coil? ammunition not shooting as hard? I dont really know what to do here. Also, does anyone know, given my coil is 40mm long, around a 6mm (5mm internal) aluminium tube, what a good ammo length and weight should be, if you happen to know or have seen someone else do it.
I dont own or intend to buy a chronograph, so how should i go about measuring the energy output for the ammunition, and is there a general way to measure my coil efficiency?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
A simple method of determining RELATIVE velocity is to clamp the coilgun horizontally and measure how far the projectile flies. If you do a few shots for each variation (capacitance, voltage, starting point of projectile relative to coil etc.) you will get a measure of repeatability/accuracy.
A ballistic pendulum is simple and can give a true measure of projectile (output) energy. Input energy is just 0.5 x C x V^2 Efficiency = (output energy)/(input energy) x 100%
P.S. if results vary for fixed conditions you could fix that first because unreliable results are .. unreliable
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(WIP) My Second coilgun, this time refined and made with effort! Mind helping me out?
