Physics for IGCSE & O level - Magnets And Currents (Section 1 - No. 21)
What would happen if you connected a DC power supply to the primary side of a transformer designed for AC?
The transformer would work normally.
The transformer would step down the DC voltage.
The transformer would step up the DC voltage.
The transformer would likely be damaged or overheat.
Paliwanag
Transformers rely on a changing magnetic field; with DC, the field is constant (after a brief startup) and the transformer will not work properly and could be damaged or overheat.