Magnetic fields and flux density
How coils, iron and air gaps combine to create the field a motor needs.
- Explain magnetic fields and flux density at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
Flux density, measured in tesla, is the single most important number in a motor's magnetic circuit — it directly sets how much force the machine can produce per ampere.
In depth
Magnetomotive force is the product of turns and current — the 'push' driving flux around a magnetic circuit, directly analogous to voltage in an electrical circuit.
Flux density in the air gap is the MMF divided by the reluctance of the magnetic path, which is dominated by the air gap because air conducts flux roughly a thousand times worse than steel.
Lab: Experiment with magnetic fields
Vary current, turns and air gap and watch flux density and force respond.
Magnetomotive force is turns times current. Flux density in the gap is that MMF divided by the reluctance of the magnetic circuit, which is dominated by the air gap because air is roughly a thousand times less permeable than steel. Beyond about 1.8 T the iron saturates and further current buys almost nothing.
Key takeaways
- Magnetomotive force (turns × current) is the driving quantity behind flux.
- The air gap dominates the magnetic circuit's reluctance.
- Iron saturation around 1.8 T caps how much flux density is achievable.
Confirm you've read through and we'll count it toward your progress.