In a Pixii-type magneto, a permanent magnet rotates beneath fixed coils and changes the magnetic flux through them. Explore that arrangement and calculate ideal induced voltage for a sinusoidal flux-linkage waveform.
Ideal Sinusoidal Magneto EMF Calculator
Enter turns, peak flux per turn, electrical frequency and an ideal external resistance. Voltage follows Faraday's law; load current and power assume a zero-impedance source and are not machine ratings.
Equation Used
- Every turn links the same sinusoidal peak flux Phi_pk.
- Electrical frequency is entered directly rather than inferred from an unspecified pole count and shaft speed.
- The external load is purely resistive and the ideal source has zero internal impedance.
The assumed sinusoidal flux linkage determines peak and RMS induced voltage. Current and power use a separate ideal resistive load with zero source impedance; real generator losses and internal impedance are not included.
Rotating permanent magnet and fixed coils
The Smithsonian describes Pixii's early magneto as a permanent magnet rotating beneath coils. The changing flux through the coils induces alternating EMF. A commutator can redirect alternating half-cycles, but it is not part of this AC calculation.
The animation shows that topology schematically and displays a sinusoidal flux-linkage assumption; it is not a field or machine-design simulation.
Faraday-law arithmetic only
Use the calculator to explore how an assumed sinusoidal peak flux linkage and electrical frequency set ideal open-circuit EMF. The ideal load readouts deliberately exclude the internal impedance and losses needed to predict a real terminal voltage, current, power or temperature.
Sinusoidal flux linkage
Faraday's law gives e=-d lambda/dt. For the separately stated ideal resistor, I=Erms/R and P=Erms2/R. Those are ideal-load arithmetic, not generator ratings.
Arithmetic example
For N=1,000, Phipk=0.001 Wb and f=20 Hz, peak EMF is 125.66 V and RMS EMF is 88.86 V. An ideal zero-impedance source feeding 5,000 ohms gives 0.0178 A and 1.58 W. A real machine will differ.
Model boundary
Real design requires the actual winding distribution, field map, magnet curve, core, air gap, speed, internal impedance, commutation or rectification, thermal limits and test data.
Magneto model questions
Is 4.44 a universal machine constant?
No. It is 2 pi/sqrt(2), rounded, for this sinusoidal flux-linkage waveform. Other waveforms have different factors.
Does ideal load power predict generator output?
No. It ignores source impedance and all losses.
Can electrical frequency be converted to shaft speed?
Only with the actual pole/event count and topology, which are not entered here.
Institutional and technical references
- Smithsonian National Museum of American History, Pixii Magneto Machine: collection record identifying the 1832 Pixii magneto generator.
- Smithsonian, Lighting a Revolution: 19th Century Preconditions: explains the rotating permanent magnet, fixed coils and generator principle.
- NASA GSFC, Induction and Magnetic Flux: states Faraday's law and illustrates a rotating-magnet magneto with alternating flux.
- NASA GSFC, Electromagnetic Induction—2: explains a rotating coil in a magnetic gap and alternating flux reversal.
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