On Wednesday 24 May 2017 19:07:31 andy pugh wrote: > So, I got one of these, and it is fun. > > But, I want to use it to heat the bases of pewter tankards to > de-solder a ring and replace broken glass bases. > > I have about 100 to fix. I sometimes wonder if I lead an unusual life. > :-)
I've been there, done that in a past life in the 1960's. > Anyway, to do that job (and I have proved that the supplied coil does > melt pewter, even though it does not couple as efficiently as iron) I > would need a much bigger and shallower coil. > > Are these cheap devices tuned for the supplied coil, or will they > auto-tune to any coil? The supplied coil is part of the tuning element, Andy. I would wind another from the same 1/4" or 6mm OD pipe, but big enough to couple to the pewter fairly close, and at the change in diameter, I'd add 3 or 4 turns to re-gain some of the inductance lost by making it bigger. Measure its frequency (I'm told to have the iron in the coil at power up, which must be a hard switch in order to get it started correctly else the magic smoke comes out of the transistors.) Set the new coil around the tankard, turn it on and measure the frequency again, which should be -25, +25 % of the original frequency. Probably it will be high because whereas the iron adds inductance and slows it down while the iron is below austenitic temps, the pewter is non-ferrous from the gitgo and will reduce the inductance even when cold. If off high by a lot more, add 2 turns to the next coil you make, or if lower, take one turn off of the new one until its running in the same ballpark. What you want is a circuit that runs at a high enough frequency to couple well to the pewter, without running so fast its spends a lot of time in the switching transition between full on and full off because the transistors aren't fast enough, which will run the transistor heating thru the roof, sometimes in very little time. That of course breaks the magic mirror and lets all the smoke out. :( Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
