Destroyed Coils

11 08 2011

All photos.

Today I removed the coils to inspect the damage from the last run.

Blown apart pretty good!

I’m attempting to clean the teflon in hydrochloric acid now.

The coils are easy enough to rewind.

There are little droplets of cooled molten copper inside the chamber!

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3 responses

12 08 2011
John B.

I’ve been following your efforts for a while. Congratulations on your recent successes! Seeing you stay on track is an inspiration for my own efforts in this area. Anyway… I’m not sure if you have already looked into it, but while the field in an inductor increases linearly with current, it also increases by the square of the number of turns. Could you get a similar field strength in the same space by using more turns of finer wire? Coil resistance goes up, of course, but 10k turns of AWG 36 puts out a nice field without a thousand amps. Also, you could put some current limiting on both the supply and the coil while working up slowly and staying well under the destructive limits of your hardware. Your superconducting grid would really help, but until then you’ll have to deal with heat. I don’t know if you look at the coils as disposable, but I would hate to see a vaporized wire send molten copper and varnish into your turbopump!

13 08 2011
keys

Unfortunately, resistance doesn’t scale linearly with wire diameter. And this is the limiting factor. If the radius of the wire is halved, this means a 4-fold increase in resistance. In addition, doubling the length (twice the turns) will cause another doubling in resistance increase, totaling 8-fold increase in resistance; whilst only gaining a 4-fold increase in magnetic field. And that is not taking into account the extra heat (which scales with resistance).

Generally, increasing turns is not a good idea. Increasing the amps is (though you might encounter cooling problems)

cheers,
keys

18 08 2011
Nguyen

Have you consider Bitter coil? (http://en.wikipedia.org/wiki/Bitter_plate)
It can stand higher current than normal wire.
Bitter coil can be cooled by liquid, which require a casing like SC coil, but at room temp and thus easier sealing and fabricating.

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