Magnetics

Magnetics covers transformers and inductors

• https://coefs.uncc.edu/mnoras/files/2013/03/Transformer-and-Inductor-Design-Handbook_Chapter_2.pdf
• https://coefs.uncc.edu/mnoras/files/2013/03/Transformer-and-Inductor-Design-Handbook_Chapter_5.pdf
• https://www.youtube.com/watch?v=xA8HalLJ92c
• https://training.ti.com/understanding-basics-flyback-converter
• https://www.youtube.com/user/katkimshow/videos

Transformer

These are just a pain to understand

Larger transformers increase hysteresis loss.

The correct frequency is critical. Ideally, the frequency should be as low as possible without saturating the transformer. Higher frequency increases hysteresis loss.

Materials

• Laminated Iron Alloyws: 1.5-2.0T 50Hz-1KHz
• Powdered Iron: 0.6-0.8T 1KHz - 100KHz
• Ferrites: 0.25-0.5T 20KHz - 20MHz

Higher tesla is associated with higher core losses, but also higher saturation.

DIY Tests

• epoxy and magnetite
• epoxy and ferrite (Fe2O3)
• laminated steel plates
• plaster as binder
• steel shavings: these are cheap and might provide a core closer to electrical steel

If I had access to a kiln I could try making soft ferrites by mixing Fe2O3 and ZnO and heating to 1500F.

Notes from "Transformer and Inductor Design Handbook"

1

Hysteresis produces core loss.

Two forces; magnetomotive force (mmf) and magnetizing force (H).

Units

• Magnetomotive: Gilberts
• Magnetizing: Gilberts/cm = Oersteds
• Flux Density: Gauss
• Resistance to flux: Reluctance

Magnetomotive Force

 mmf = 0.4πNI
 N: number of turns
 I: current

Magnetizing Force

 H = mmf / MPL
 MPL: magnetic path length

Flux Density

 B =μH
 μ: permeability of core

2

Core materials

• silicon steel
• nickel iron (permalloy)
• cobalt iron (permendur)
• amorphous metallic alloys
• ferrites

Two primary magnetic losses; hysteresis and eddy currents.

Silicon steel is more stable (than just steel) over time and reduces eddy currents. Good in the lower range. High stauration flux density. M6 grain-oriented steel is particularly good.

Nickle-Iron (Permalloys). Supermalloy is a good variant.

Powder iron cores are cheaper. Require more turns.