#### localbroadcast

##### Newbie level 3

This may be a very basic concept that I should know, but for some reason I can't figure out the logic behind it!

I want to know what the reason is for choosing the number of turns to use for the primary winding of a transformer.

I understand that if I have 10 turns on the primary and 1 turn on the secondary, and apply 120v to the primary, then I will get 12v on the secondary.

The question is... If I was designing a transformer, why would I choose to use 10 turns on the primary and 1 turn on the secondary? Why wouldn't I choose 20 turns on primary and 2 on secondary? Or even 1000 turns on the primary and 100 turns on secondary?

I know there has to be more to choosing the number of turns than just the ratio! Anyone want to shed some light on this topic? Thanks!