finding Al of toroid

Thread Starter


Joined Apr 3, 2009
what im trying todo is find the AL of a toroidal core. i found the formula online. Al = H/T^2. where H is henries and T is number of turns. im doing this experimentaly by wrapping 10 turns on the core and measuring inductance. im finding some discrepancies about the units. could someone please explain what units to use? i need a core with an AL greater than 4000. for example, on the first core i tried, i used 10 turns and measured .57mH. (btw, my meter only goes 2 decimal places on the lowest scale of 20mH) not sure if im using the right units, but if i take 570000nH/10^2 i get 5700. is this right? thank you!

Ron H

Joined Apr 14, 2005
If your requirement is for AL > 4000 nH/T^2, then your calculation is correct. You should measure the inductance at a frequency that is within the range in which you intend to use it.