I’ve been studying the past couple of months some ways to improve the field coil performance and in a way to make my tools better, to sharpen them. My goal is to get the most flux density in gap for a given current in field coil.
I tried many magnetic circuits meant to take advantage of the shape of a field coil because being a solenoid it will work better having a length per diameter ratio above unity. Works better means a more uniform field in the core.
I managed to get a simulated result of 1.5T in a 1mm wide and 12mm high gap using standard 1010 steel and a field coil consuming 7.231 Watts!
The field coil is made with 1 mm EC wire so it will be able to handle a lot more current. You will get more flux density this way but the curve will get more and more bell-shaped.
As you can see for 1 Amp you get a very nice increase in flux density. Its not as linear but the difference is small.
There is a balance, hard to achieve, between linearity and maximizing flux density. And this has to do with the magnetic circuit and saturating the pole plates. I usually want to saturate them right at the gap. This way it’s less prone to modulation.
In placing the saturation area, the central pole piece and the top plate geometries have a large role. Always remember that the thin parts of steel saturate faster and zones with transitions from one dimension to another or sharp angles are also prone to saturation.
Below you can see a motor with a linear flux density curve over a 20 mm travel. The central pole piece is of the same diameter as before. You can see that making the top plate thicker killed the saturation around the gap. To bring it back, we must use a larger diameter for a voice coil. But more on that in a future article.
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