I used 4 identical cores and circuits with the only variable being the number of turns (and hence inductance) to determine how to make the most efficient Joule Thief. The cores had respectively 20 turns CT, 40 turns CT, 60 turns CT, and 92 turns CT. I also included a core made from a flyback transformer which had 120 turns CT. Each circuit was powered from a new fully charged rechargeable battery.
The circuits with the least number of turns died first (~2 days) and the flyback circuit is still running strong after 9.5 days. So it appears that more turns (and larger inductance) produces a longer life. I tabulated the results in the video.
You might want to look at the other videos I made on the Joule Thief
Part 1: How to make it and how it works:
https://youtu.be/TOblG6482gk
Part 2: Exploring the Joule Thief - how different components affect the cicuit:
https://youtu.be/xOrOaXiH6VM
