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Ferrite Core Coil-Winding Considerations

May 14th Fact-of-the-Day

The mechanical properties of various types of ferrite vary. However, ferrite is a ceramic that generally breaks rather easily. It should not be dropped or pressed tightly in a vice, not only because it may break, but because mechanical stress tends to change its permeability and loss characteristics. Be especially careful winding large-diameter solid wire on a small diameter ferrite core, because winding pressure may break or cause micro-cracks in the ferrite that will change its characteristics. Windings should conform to the ferrite wall shape as closely as possible for the best possible magnetic coupling to the core, but it is difficult to bend large diameter wire to conform closely to core shape without mechanically damaging a core at its corners. A solution to that problem is to use two (or more) smaller diameter wires in parallel, rather than a single large diameter wire. A coil wound that way tends to have lower losses because of improved magnetic coupling and the finished product is smaller in size. ©2005 Martek International All rights reserved.

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