To determine the primary turns you need to know the Bmax of the core you want to use, the crossectional area, frequency and voltage of operation.

Than you apply the formula according to your situation, if pulsed dc, or square or ac wave.

Once you know the primary turns you can set the other secondary needed turns.

Thats because you are using the equation to determine how much flux is allowed into this transformer.

I was thinking a transformer does not offer a BEMF like motors do when they speed up.

You draw current from the secondary you reduce the primary inductance and lot o current go in...

I'm thinking a way to have a kind of BEMF of motors inside the transformer to help it become a generator of energy and not a transformer...

I don't know if its impossible...

1Henrie = 1volt*1second /1amp

This mean if you apply 1 volt to a 1 henrie coil in 1 second 1 amper will be flowing

If you than multiply the Bmax of the core material to the crossectional area in m2 you get the maximum flux allowed on that core in webbers.

And the turns become = V/Webers/Frequency/4,44 for AC

If i remember well

I posted it some time ago ion my projects section somewhere...