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Registered Member #396
Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176
Dr. Kilovolt wrote ...
I thought the positive electrode actually gets hotter, because of the electrons flying off the negative electrode and hitting the positive one.
Thats what I though too. When TIG or stick welding with DC, the positive electrode definitely gets hottrt. Usually the workpiece is made positive and when TIG welding, your tungsten electrode is negative. Its interesting to note that when welding aluminum one usually needs to have the workpiece negative at some point (by using AC or modified square waves) because this situation has a cleaning effect and removes oxides.
From a Miller welding handbook "approximately 70% of the heat will be concentrated at the positive side of the arc".
Also "Positively charged gas ions trike the workpiece with sufficient force to break up and chip away the brittle aluminum oxide".
And from Wikpedia "Xenon short acr lamp" - "Electrons passing through the plasma cloud strike the anode, causing it to heat. As a result, the anode in a xenon short-arc lamp either has to be much larger than the cathode or be water-cooled, to dissipate the heat."
So can we say that electrons striking a surface cause it to heat more than gas ions striking a surface?
haxor5354, are you sure your flyback isn't AC and the "ground" (not red wire) terminal isn't simply larger so its not melting?
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
I have a DC flyback from a CRT monitor, and I'm in the same situation as haxor5354, the negative terminal gets much hotter than the positive even with the same electrodes. I'm also pretty confident in the polarity of the terminals because I have used an LED in the current path and it only turns on in one direction.
I can't think of a particularly good reason for it unfortunately.
banned on 5/26/2009 Registered Member #1877
Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147
When me and yottakva rewound a mot and put 4 windings of 6 gauge wire, we found that nails and bolts would go red hot from the anode as well. is there any definitive answer as to why??
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi, In RTG bulbs it is the anode which needs to be cooled properly. So it looks that the observed phenomenon is not related to the electrons but to the gas ions. I think the effect you experience is similar effect like when you use aqueous solution of salt as anode and than burn a plasma discharge between this kind anode and a cathode made of metal. The metal will melt very quickly (including tungsten) because the anode emits gas ions releasing its energy after hitting the cathode. Check this for the melting cathode example which can even melt the ceramic insulator around the electrode
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why does the negative electrode get so hot?
