Fig. 7. Coils placed on top on one another, same orientation:
1.312 mH
Never do this.
Interesting. I wonder how this differs from coils placed in parallel with the same orientation rather than in series? Earlier in this thread, it was discussed that coils placed in parallel this way would provide 4 times the inductance. I read this as, for example, two 1mH coils stacked in parallel would be .5mH times 4 would be 2mH.
( For the same value coils ) + when stacking air-cored coils you'll most likely get a Mutual Inductance that increases your "halved" inductance by only a multiplier of something less than 1.5 ( with the coil windings going in the same direction ).
eg. 2x 1.3mH coils wired in parallel ( and separated by more than 4 inches ) will now measure as a .65mH coil and have half the DCR ( measured with S&L's WT2 ).
- Stacking these 2, 1.3mH coils with the windings going in the same direction will now measure @ 0.925 mH coil with half the DCR.
- ( this, using Solen "perfect-lay" coils = a coil that has the same height as measured from outside of coil the beginning of the hole )
The "doubling factor" mentioned earlier is very misleading and won't happen in your circumstances.
Stacking the paralleled coils but flipping them so that the windings oppose each others magnetic field will result in a net inductance smaller than the value measured when the 2 coils are spread apart.
eg. The same paralleled 1.3 mH coils stacked ( but opposing each others magnetic fields ) results in an inductance smaller than 0.4 mH .
As everyone keeps saying > measure your results with appropriate equipment before proceeding to your network design phase.
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