This question is related my my previous question: What to do about very hot planar inductor?
What I'm trying to do
I am trying to make a planar inductor (made from the tracks of the PCB, and surrounded by a 2 part a ferrite core). According to the datasheet of the ferrite core, the AL value is 1700nH, which means that with 12 turns around the core, I should get 12x12x1.7 = 244uH.
However, when I measure the inductance on my LC meter, it reads only 1.8uH. What's stranger is that if I create an inductor with the same core, but using stranded wire, and only 10 turns, I get 46uH!
I measured the resistance of the PCB tracks, and it's 0.25R, just as it should be, so I don't think there's a short in there.
What's going on? Is the AL value not sufficient for calculating inductance? How could it be that fewer turns gives a much higher inductance? Is the stranded wire massively better than PCB trace?