Why can't transformer dc transformer?

Transformer can mini electric motor change voltage condition is that the original edge to ac electric potential to produce alternating magnetic flux,alternating magnetic flux will be produced at the edge of the deputy induction electric potential,the size of the induction electric potential is proportional to the change rate of flux.When transformer dc trendy,due to the current size and direction are the same,no alternating magnetic flux in the core,namely the constant flux and flux rate is zero,so the induction electric potential is zero.At acmotor2.blogspot.com that moment,all the dc voltage applied in winding with electric motors pricesmall resistance,the current is very large,approximate short circuit phenomenon.

And alternating current (ac) is the change alternately,when access to primary winding alternating current (ac),also with the change of the formation of magnetic flux in the core,is greater than the primary and secondary turns,can increase the voltage;On the other hand,the secondary coil number less than primary can buck.Because of the size of the direct current (dc) and the direction does not

change with time,so constant direct current into ac electric motor the primary winding,the core flux was constant,cannot in the secondary winding induction potential,so no pressure.