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I did it with FEMM, but for different coil shape. Even in saturated case (~5T) iron washers at the ends are highly beneficial. Even shortening the wire space replacing it with additional iron washers seems to be more efficient. 1/5 more efficiency with washers, I would say from top of my head. But keep in mind increase in fuko currents losses, which in practice lower efficiency of high stages with short pulse times. Powdered iron should lower this effect, but I just didn't collected enough iron scrap to wrap it all over my coils.
I doubt the density of the steel particles is high enough to make any difference - you will need to add iron filings anyway.
Why wouldn't you just use iron washers at the ends of a coil and cover it with piece of wide iron pipe? This will work perfect for sure. This stuff is easily available at Home Depot.
I also tried a ferrite EMI supressors (ferrite halves used to be putten on cables) as external iron - with those coil gives around 10% more energy to the projectile.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
I think [JB WELD] probably should work, the permeability of iron/steel is very high, diluting it like that, even a few percent should make a huge increase in permeability over that of air.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
I did some more analysis of the chain of coil/capacitors.
It looks like you put a capacitor in parallel with each coil, and then put the coil/caps pairs in series in a row, each tuned to a higher frequency than the previous coil, and drive them from one end with the right kind of signal (roughly speaking a rising tone, but it's more complicated than that). I think you need two or three chains as well to give phases.
I haven't finished analysing it yet though, there's interactions between projectile length and q factors, also the presence or absence of the projectile changes the inductance. It may be you need a projectile that's several cycles long for it to work, but it looks interesting.
Registered Member #9349
Joined: Mon Jan 07 2013, 08:50AM
Location: France
Posts: 102
Hi, first, I am amazed by the quality of your work !
I have a few questions about your design :
I don't understand the meaning of "diodes that commutate", could you explain a little please ? Is it just diodes put across the coil in anti-parallel configuration to absorb and circulate the back EMF produced by the coil ? Why putting 4 diodes in series hasten the current drop in the coil more than just one ? Is it due to Vforward drop of each diode that stacks ?
As you are working under relatively low voltage (50v) why do you use IGBTs ? Would it possible to do the same job with mosfets ?
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New Coilgun Project
