What if the primary coil of a transformer was connected without the iron core and the secondary coil?

Question

I'm trying to create an electromagnet from a microwave oven transformer. The secondary coil will be removed, and the top of the transformer (The I in the E-I transformers) will be sawed off (to increase field strength).

My DC power supplies can only supply low currents (12 V @ 5 A, 20 V @ 2 A) since it's DC, so I thought that AC current might be better. I'm not that familiar with using AC. The problem right now is that I'm unsure whether removing the secondary coil and cutting the top off will cause a short circuit issue.

This is because I had read somewhere that the impedence comes from trying to change the magnetic field of the iron core (in between the cycles). With part of the core removed, would that cause any problems?

To clarify further: The only thing keeping the primary coil from short circuiting is the flactuating magnetic field (trying to change the magnetic field of the iron core). So with part of the core removed (only the I part of EI), would that cause any issues?

Thank you for your time. Any related articles/resources would also be helpful.

Note: I'm using 240 VAC @ 50Hz.

Answer 1

Opening up the core will drastically reduce the inductance of the transformer, which will result in drastically increased current for a given AC input voltage. Applying 240V to a transformer with the core opened up may well result in smoke.

If you must do this get yourself a variac so that you can gradually increase the voltage while measuring the current to ensure it doesn't get excessively high.

Answer 2

Using AC you can be sure that the "electromagnet" will not be a short circuit as it has some pretty high inductance. But would the electromagnet powered by AC have any use for your problem? Maybe you could describe more how you will use the electromagnet.

Feeding the electromagnet with DC certainly means that the only thing limiting the current is the coil resistance. In practice, your power supply will fail to deliver such a high current and you won't get near the expected magnetic field strenghts and even probably damage your power supply.