I have some troubles to understand the principle of: 1-> open core inductor 2-> open core transformer
Let us talk about open core inductor as the one above:
If we think about it as an equivalent magnetic circuit, we get:
And the reluctance of the air is rougly bigger than the reluctance of the core and then the reluctance of the core is negligible. So the flux into the inductance does not depends on the core. And as the inductance is proportionnal to the flux, why do not just remove the core?
So it is probably a problem of coupling? But I do not understand what is the purpose to have a great coupling between the windings of the core? It is an inductance, so it will just add some "leakage" inductance? Inductance + leakage inductance = inductance. What is the problem?
- Then here is a transformer with an open core:
This is actually an induction coil. Nevertheless there is two coils which are wound around a common core. For having a good transformer we need to have a large variation of magnetic flux according to the time as indicated by Faraday, but in this case, we reduce the maximum of flux as we have some of the flux which has to travel through the air. So for the same number of turn and the same intensity, we have a flux which is lower than it could be if the core were closed. It might be better to have less turn (or less intensity) and a core closed for doing the same experiment? Did I do a mistake? In this case I understand that we need to have a good coupling ;)
Thank you very much :)