Transformer

Very good, next?

I was just showing someone how to wire the transformer so it wasn't wired like two inductors in series.

Just came across the circuit you are talking about, this circuit should do the trick.

But what is it doing? Sorry i am new in electrical things... And sorry for my english i am from Germany:)

In this case it is working as an isolation transformer because it is not stepping up or down the voltage. In this case you could short out the circuit on the secondary and it wouldn't damage the power source since there is not direct wire to it. You can change the ratio of the transformer to make it a step up or step down from here. The way you had it wired was as two inductors in series. All that did was block the ac voltage, and you're trying to pass it through the transformer. The only reason it worked is because you set the ac power supply to have 3 volt dc power to go through it. Transformers only work with ac, unless you wired them how you did, then it is set as two inductors with block the ac but pass dc.