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Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
does not matter at all. L/R is important.... the question is: increases the iron wire the inductance compared to copper wire? and how would the coupling be... i kind of suspect that te coupling is not so good, since the magnetic field is allready happy inside the coil.. hmmmh. simulation incomming^^ but i have not the time right now.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
You don't want iron within your turns, it would short out the magnetic field; you want the core material all inside all the turns; none of it in the actual windings, otherwise you'll get no field external to the windings at all, the lines of flux will close within the turns themselves; it's a magnetic short circuit.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
@aarpcard, I put a strong Neo magnet to the tube of JB-weld: it REALLY pulls! (NOT the hardener)..I haven't thought of it WRT coilguns yet, but definitely will right away. I am also extremely anxious to know your (and other's) thoughts too!
Registered Member #2848
Joined: Tue May 04 2010, 05:19AM
Location:
Posts: 44
I don't want to risk messing up the coils in this build by potting them in JB Weld. I do however have a smaller coil I built for a past gun I'm not using that'd I'd be willing to test on.
I'll get some baseline readings and see how JB weld affects it. I suspect BigBad is correct though.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
The bit about damping resistors and train-braking resistors reminded me of a cast-iron artifact in my collection.
For home-made damping resistors, don't forget the large temperature coefficient of copper (not far behind that of tungsten). When temperature has risen 100 degrees C, the resistance has increased by 40% or 50%. If temperature doesn't get that high during sustained firing, you are wasting space and material. Metals like nichrome (or stainless steel, or plain steel) have high resistivity to begin with, and smaller temperature coefficients.
An Internet search found serpentine iron resistors in a picture halfway down this blog page, under June 18, 2010:
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3-Stage Coil Gun - (Quest for 200m/s)
