I found two CFLs (compact fluorescent lights) that were dead, so I opened them up to see what happened. Both self destructed when the components burned up. I decided that most of the parts were damaged by overheating and unsalvageable, so I took the toroids out and threw most of the rest away. As can be seen in the picture, the core on the right was burned by the other overheated parts. But not to worry; like the One Ring, these ferrites were forged in the hottest fire, and a little singeing of the paint doesn’t hurt the core at all. Just remove the wire and clean it up, and then rewind it with some new wire. Both cores were about 3/8 inch O.D. or about 9 mm, which is a very nice size for a Joule Thief.
As can be seen, the right core was wound with a winding of 7 turns, which I left on to measure the inductance. The 7 turns measured 38 microhenrys, which is on the low side for a Joule Thief. I will remove the (possibly overheated) wire and rewind the core with two windings of 12 or more turns, using 30 AWG or 0.25mm enameled wire. This should give at least 100 microhenrys per winding, which is a good value to use for a JT.
