When the winding gets tough, double up the number of toroid cores, I say. This JT uses toroid cores that are less than 1/4 inch (6.4mm) outside diameter. The wire has to be fine to get several inches wound on a core. So I wound one core with the wire, and then coupled it to a second core by putting a single turn loop of heavy wire through both and soldering it. Then the second core could hold the remaining turns of wire. The cores are closely coupled electromagnetically, so they sort of act as a single core.
The cores don’t have to be small to be coupled together with a single turn. Two large cores could be coupled, as could two cores of different sizes. However, if they’re different sizes or different magnetic properties, that may affect the way they work in the Joule Thief. I’ve never seen any documents on this method, so I wouldn’t know what to expect if they were different. This might make a good topic for some major experimentation. Perhaps someone could use it as a topic for a thesis in college.
Back to experimenting…
