How does a solenoid work?
When the iron core is applied to the solenoid coil, the iron core is magnetized by the magnetic field of the solenoid coil. After magnetization, the iron core becomes a magnetic field, two magnetic fields will increase the magnetism of the solenoid. In addition to, the solenoid cannot be made of steel, or once steel is magnetized, the magnetism cannot be controlled by the current, the advantages of the solenoid will disappear.
The solenoid is the impermanent magnet, it is easy to start or end the magnetism. For example, on-off solenoid valve or lifting electromagnet.
In general, the magnetic field of the solenoid is related to the current, coil turns and the iron core inside solenoid. So that, in the process of the solenoid design, we should focus on the winding distribution and iron core selection, and use the size of current to control the magnetic field. Due to the coil resistance, the size of the magnetic field is limited, with the discovery and application of superconductor, the limitation has chance to overcome.
A miniature transformer with E-type iron chip (note: F-type iron chip is useless);
Tools: a pair of pliers, a normal screwdriver;
Find a transformer (it's easy to be found in many electric appliances.) and split it. Split the first iron chip slowly with a pair of plier and a normal screwdriver, and then, you can take the chip a little hard.
After dismantling, you can find the transformer has two coils, one has thin enameled wire, and another one has thick enameled wire. Choose the thinner one.
Next, we should take the voltage into consideration. If the input voltage of the transformer is 220V, the output voltage is 12V, and you choose the coil with thinner enameled wire, so the voltage of your coil is 220V. But, if you choose the coil with thicker enameled wire, the voltage of your coil is 12V. In fact, here is just a reference, you should choose relative voltage according to the parameter of the transformer.
Reinstall the transformer, notice that reinstallation is not just like before, you should put protruding edges on the same side, instead of cross stacking like before.
Finally, put the coil on the iron chips. Until this step, your solenoid is complete.