Transformer - Powered by DC?

A transformer will NOT operate on DC. The winding will short out the DC supply and you will get nothing out of the other windings.

A transformer works by a constantly changing magnetic field that the AC current generates. With DC you get no change in the current and no change in the magnetic field.

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No. a transformer cannot be powered by AC.because due to the steady flow of current in dc,it will not create any disturbances in the secondary coil in transformer.

A transformer uses magnetic flux changes in the primary coil for induce a voltage in the secondary coil, the relation between the voltages is given by:

Vsec = N2(dΨ1/dt) (Faraday's law of induction)

Ψ1 = k*N1*I1

Then Vsec = N2(k*N1*dI1/dt) where:

N1: number of turns in primary coil

N2: number of turns in secondary coil

Vsec: Voltage in secondary coil

Ψ1: magnetic flux in primary coil

I1: current in primary coil

k: constant involving Reluctance and others parameters

If the current in the primary coil is DC (a constant) then his derivative must be zero, then Vsec = 0

I once powered my transformer from DC with LED on other end. the LED glowed for a fraction of second and then went off

Direct current (DC) is not transformed, as DC does not vary its magnetic fields