How many turns?

You only want to charge a balance 2-3 times, regardless of how large the window is. If 2-3 times isn't enough, then give it another 1-2 turns. We highly recommend that you never go much more than that, or you risk damaging the spring. If that doesn't do it, then the spring is too weak for the sash weight and no amount of turning will give you enough tension. You would need a new balance with the proper spring strength.