Posted by aonomus on September 3, 2008
So I just finished lashing together and test firing my coilgun, I’ve tested it with 400V at 4800uF using a nice sized coil. For now its experimental, however I may add more windings or simply just increase the capacitor bank size.
At the moment, the coil (18AWG 32 windings x 4 layers) heats up after a few firings and is connected to the capacitor bank which has been tested up to 400V. The firing circuit is simply a 9V battery, a 82ohm resistor and a pushbutton switch connected to the SCR.
The charging circuit is connected directly to the charging circuit, however I should have a DPST or DPDT switch to physically disconnect the bank from the charger.
The SCR is mounted onto a short flattened copper pipe with 2 other holes for mounting.
My next step is to build a much larger bank of 200V or 300V capacitors as they are more available to me. Using bigger SCRs or multiple paralleled SCRs may be an option to increase pulse current and faster charging can be obtained via directly rectifying AC mains. 200V or 300V capacitors are usually used when 120VAC is rectified to 170VDC, thus they are more commonly available.
Energy is obtained via the formula E=0.5CV^2, since C = 4.8×10^-3 and V=400, E=384J, however by decreasing voltage to 200V, E drops to 96J and in order to obtain the same energy, capacitance must nearly triple. Substituting a 400V cap bank for 200V is a fairly poor choice, however some coilguns have been designed so well that efficiency is good. Losses in this particular coilgun are in the projectile shape/size sticking in the barrel at times, and also likely back-EMF losses.
Now for the comedy gold: