I built this transformer core out of 30 mm mild steel. It is 13 cm by 8 cm. The primary winding is 30 meters of #29 wire, and the secondary is 60 meters of #29 wire. The windings measure 5 ohms and 10 ohms. A 100-ohm resistor is across each winding to absorb voltage spikes.
When I apply a 15 volt pulse to the primary, the secondary only produces 5 volts. The core will have eddy currents, and is not the most efficient design, but 17% efficiency seems overly low. I tried resetting the core magnetic field by applying reverse voltage, but it has no effect on the output.
The 15 volts on the primary seems to produce a very strong magnetic field, the pieces of steel are locked together when it is energized. But this field does not seem to induce any significant voltage in the secondary.
Am I having massive hysteresis loss?