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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Re. the metallurgy. I can attest that asphalt composition shingles in California are generally attached with galvanized steel nails. And that copper roofing nails (used e.g. with sheet copper flashing) are the same non-magnetic copper alloy all the way through. Harder than electrical copper, but galvanically about the same, and the color (before and after weathering) is the same as the sheet copper. Scroll down at - - - You can determine the actual current in your nail-melting experiment with reasonable accuracy by using one of your copper cables as a current shunt. Measure the immediate voltage drop in one wire, avoiding the contact points. Look up the ohms per foot for that wire gauge.
The voltage drop may well increase, second by second, even though we know the current is drooping. That's because the wire is heating up and significantly increasing its resistance.
I would not trust a current calculation based on nominal battery voltage and calculated loop resistance, even including battery ESR from datasheet. But think that 5000 amps is achievable.
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329
Beryllium copper could be used for nails, its quite strong compared to pure copper. Its what copper springs and a lot of pin for electronics are made from. Though I suspect california may have issues with the beryllium, and maybe even the copper as thats obviously toxic, given its anti-microbial properties...
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
The copper nails are not just work hardened copper (I know because I annealed one and it's still quite hard) but they are certainly not copper clad steel. If I get very bored I might analyse one. It might be interesting to compare the new ones and the originals (roughly a hundred years old). I doubt the are Be Cu because that's expensive as well as toxic.
Meanwhile, back at the topic. You could estimate the resistance of the cables by looking in a table of wire properties, but I wonder just how accurate that would be. (even a little work hardening of copper increases the resistance considerably.)
It would be better to calibrate the measurement by measuring the voltage drop along the cables with a known large current like a car headlight and battery or some such, and extrapolate from that
Registered Member #3950
Joined: Wed Jun 15 2011, 12:45AM
Location:
Posts: 51
You should use the massive current that battery can supply to make a rapid fire coil gun! Unlike with capacitors, you would have no charging time in between shots, so you could probably shoot extremely fast with a good switching mechanism.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Yes, the voltage would be dropped internally by the resistance of the battery with a superconductor. And the heating would also be confined to the battery...
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Fun with 5 kiloamps
