In my last installment I briefly mentioned that soldering copper is difficult with induction heat. That is true unless one uses a flux concentrator. Well lo and behold we had a kit customer who was interested in heating small parts which also requires a flux concentrator so I took some time out to experiment.
A flux concentrator is simply something that is magnetic and suitable for the operating frequency that concentrates the magnetic flux into a specific area. Pictured above is a simple concentrator that I made using a broken transformer core. This is attached to the output of a Roy heater. The white-hot object is a 1/4-20 steel nut. I melted the nut right after this photo was taken!
The flux concentrator can concentrate the magnetic flux into a very small area which is what is needed for heating highly conductive metals such as copper and brass.
Above is a photo of a brass bolt that has been melted by the flux in the gap. The bolt has been repulsed by the high magnetic field and was physically moved out of the gap before I could take the photo. Power in this photo is about 500 watts.
Here is a photo of a heavy duty crimp-type butt splice in the gap. With about 500 watts input to the heater, this splice is heated from room temperature to soldering temperature in about 15 seconds.
Other things to note in the photo include the Litz wire used to wind the work coil. This wire, which is made up of hundreds to thousands of individual strands Has much less resistance to RF current than conventional wire because of the skin effect. Current flows on the surface of hundreds of little wires instead of one big one. This wire is available from Fluxeon® .
Here is another shot of the flux concentrator. The gap has been opened up so that I can fit a 3/8″ copper coupling in the gap to demonstrate copper sweating.
Here is the soldering operation being conducted.
And the finished product. Note the complete lack of staining or other evidence of heat. Also note the almost perfect little bead of solder. Notice that the copper tubing is in contact with the plastic tape holder (the tan object in the background) but the copper isn’t hot enough to melt the plastic. That’s how fast induction heating can be.
The kicker: From room temperature to soldering in 7 seconds! That’s with about 700 watts input to the heater. Probably half that makes it to the work.
While Fluxeon® does not (yet) offer a soldering heater, you can easily make one from the kit that we offer. When you order a version 2.21 kit, be sure to note that you want to do copper soldering. You will be supplied with a different output transformer. This transformer has 20 turns of Litz wire on the secondary instead of the 2.5 turns of welding cable used on the general purpose heater. You may also buy more litz wire and ferrite cores for the flux concentrator. Contact me or Garett, [email protected]  for more info.