10/28/19

Understanding Solenoids

In order to understand and spec solenoids for punching, we did some review on electricity and magnetism to bring our electrical team (aka Meg) up to speed on the relevant physics. Despite all of the complicated derivations, the electric field generated by a solenoid can be simplified to B = k μ0 n I, where B is the field, μ0 is the permeability of free space, n is the turn density, I is the current, and k is the relative permeability of the core. The current draw is directly related to the resistivity of the coil material and its cross-sectional area, so increasing the number of turns increases the resistance of the coil and decreases the current draw, therefore having no effect on the magnetic field. The solenoid can, therefore, be thought of as power limited, with any balance of voltage and current being acceptable as long as the total current is the same. From there, it is only about choosing a core with high magnetic permeability such as iron (5000μ0 when pure) to allow a strong field to build and a large amount of force to be transferred.