Magnetomotive Force Converter
Convert magnetomotive force units — ampere-turns, gilberts, kiloampere-turns, and more. Free online MMF converter for magnetic circuit design and electromagnetic engineering.
Understanding Magnetomotive Force
Magnetomotive force (MMF) drives magnetic flux through magnetic circuits. You express MMF in ampere-turns (A·t), representing current times number of coil turns. MMF is the magnetic equivalent of electromotive force (voltage).
MMF creates magnetic field strength in a circuit. Higher MMF produces more flux, limited by core saturation. Transformers, motors, and relays all rely on MMF for operation.
Magnetomotive Force Formulas
F = N × I
Definition: MMF equals number of turns times current in amperes. F represents magnetomotive force in ampere-turns.
F = Φ × R
Hopkinson's Law: MMF equals flux times reluctance. This is the magnetic equivalent of Ohm's law.
F = H × l
Field relationship: MMF equals magnetic field strength times magnetic path length.
Example: A relay coil with 1,000 turns carrying 50 mA produces F = 1,000 × 0.05 = 50 ampere-turns of MMF.
Common MMF Conversions
| Ampere-turns (A·t) | Kiloampere-turns (kA·t) | Gilberts (Gi) |
|---|---|---|
| 0.7958 | 0.0007958 | 1 |
| 1 | 0.001 | 1.257 |
| 10 | 0.01 | 12.57 |
| 100 | 0.1 | 125.7 |
| 1,000 | 1 | 1,257 |
Magnetic Circuit Parameters
| Electrical | Magnetic | Relationship |
|---|---|---|
| EMF (V) | MMF (A·t) | Driving force |
| Current (A) | Flux (Wb) | Flow quantity |
| Resistance (Ω) | Reluctance (A·t/Wb) | Opposition |
| Conductivity (S/m) | Permeability (H/m) | Material property |
Practical Applications
Relay and Contactor Design
MMF determines pull-in force. Typical relays require 50-500 A·t. Holding MMF is lower than pull-in MMF. Air gap size affects required MMF significantly.
Transformer Excitation
Magnetizing current creates MMF to establish core flux. No-load current is 2-5 percent of rated current. Core material and geometry determine excitation requirements.
Electromagnet Lifting
Lifting capacity depends on MMF and air gap. Scrap handling magnets use 5,000-20,000 A·t. DC excitation provides constant holding force.
Magnetic Amplifiers
Control winding MMF modulates core saturation. Small control MMF regulates large load current. Used in high-reliability power control applications.
Frequently Asked Questions
What is the difference between MMF and EMF?
EMF (electromotive force) drives electric current in electrical circuits. MMF (magnetomotive force) drives magnetic flux in magnetic circuits. Both represent driving potential.
What is a gilbert?
Gilbert is the CGS unit of magnetomotive force. One gilbert equals 0.7958 ampere-turns. The unit honors William Gilbert, pioneer in magnetism research.
How does air gap affect MMF requirements?
Air has much higher reluctance than iron. Most MMF drops across air gaps. Doubling gap length approximately doubles required MMF for same flux.
How do you calculate reluctance?
Reluctance equals path length divided by permeability times area. R = l / (μ × A). Total reluctance sums series reluctances like resistances.
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