500 RPM baseline
66.67 Hz · 15.39 V phase RMS · 21.76 V adjacent line RMS · 30.78 V opposite line RMS. Compare the voltage of the connected terminal pairs with your converter range.
4 Phase Dual Axial Flux Permanent Magnet Generator Calculator
Screen phase voltage, adjacent and opposite line voltage, and frequency for a four-phase, dual-rotor, single-stator design. Free, instant and no sign-up. Continuous power requires a separate load and thermal analysis.
Four-phase describes the electrical phase count, not a 4 kW output rating. Dual describes two rotors facing one stator.
Use the calculatorCalculation notes updated ·
How to use and interpret the estimate
- Set speed, poles per rotor and the active magnet annulus dimensions.
- Enter peak air-gap fundamental flux and total series turns per phase. The fixed winding factor 0.95 is an assumption.
- Verify four equal phase EMFs at 0°, 90°, 180° and 270° with a common neutral. Read the adjacent or opposite terminal voltage for your connection, then export the assumptions for review.
| Quantity | Equation and assumption |
|---|---|
| Frequency | f = P × RPM / 120; P is poles per rotor. |
| Active area | A = π × (Do² − Di²) / 4, with diameters in metres. |
| Flux per pole | Φ = (2/π) × Bpeak × A / P. Ideal sinusoidal field, uniform radially; leakage and pole-arc effects not separately modeled. |
| Phase RMS EMF | E = √2 × π × f × N × kw × Φ (about 4.44 × f × N × kw × Φ), kw = 0.95. |
| Line RMS voltage | For equal phase EMFs sharing a neutral, Vpair = 2 × E × |sin(Δθ/2)|. Adjacent phases (90°): √2 × E. Opposite phases (180°): 2 × E. Derived by phasor subtraction; open-circuit AC, not rectified DC. |
4-phase vs 3-phase generator voltage: which model fits?
Start with the winding connection and converter input. The comparison below holds phase RMS EMF E constant; it does not compare equal-size machines, copper use or available power.
| Connection | Terminal pair | Line RMS voltage |
|---|---|---|
| 3-phase star | Any two phases, 120° apart | √3 × E |
| 4-phase common neutral | Adjacent: A–B, B–C, C–D, D–A (90°) | √2 × E |
| 4-phase common neutral | Opposite: A–C, B–D (180°) | 2 × E |
These factors follow from Vpair = 2 × E × |sin(Δθ/2)|. More phases alone do not prove higher efficiency, lower torque ripple or fault tolerance. Those require the actual winding, load and control strategy. A three-phase bridge model cannot directly describe a four-phase converter; isolated windings and separate bridges also need a connection-specific model.
Use the 3-phase dual AFPM calculator for a three-phase windingTwo examples to compare
Both use 16 poles, 300/200 mm active diameters, 0.7 T peak field and 50 series turns per phase. These are illustrative inputs, not product specifications.
100 RPM low-speed case
13.33 Hz · 3.08 V phase RMS · 4.35 V adjacent line RMS · 6.16 V opposite line RMS. Voltage falls with speed; increasing series turns also changes resistance and available current.
Reproduce the 500 RPM case: A = π × (0.3² − 0.2²) / 4 = 0.0392699 m²; Φ = (2/π) × 0.7 × A / 16 = 0.00109375 Wb; f = 16 × 500 / 120 = 66.6667 Hz. Substituting N = 50 and kw = 0.95 into the phase EMF equation gives E = 15.3881 V. Then √2 × E = 21.7621 V and 2 × E = 30.7762 V. Keep full precision until the final displayed result.
Load either example in the calculator ↑Design boundaries to verify
Winding Factor Assumptions
The assumed winding factor is kw=0.95. Actual winding factor depends on coil pitch, distribution and harmonic order; derive it from the winding layout before using the voltage estimate.
Thermal Limitations
No continuous power rating is inferred. Specify conductor size, current, winding resistance, losses, cooling and duty cycle, then verify temperatures under load.
Structural Constraints
Dual-rotor architectures experience intense magnetic attraction between rotors. Deflection must be carefully analyzed to maintain a consistent airgap under operating loads.
Frequently asked questions
Tool & Methodology
How is the output voltage calculated?
Ephase = √2 × π × f × N × kw × Φ, with kw=0.95. This is the sinusoidal open-circuit RMS EMF, not terminal voltage under load. Flux per pole comes from the ideal annulus model shown below.
Why does changing poles leave voltage unchanged here?
In this model, frequency grows with pole count while flux per pole falls by the same factor. Voltage stays constant at fixed RPM, geometry, field and series turns. Real designs can also change leakage, winding factor and losses.
Can this tool establish rated power?
No. A kW rating requires load current, power factor or rectifier behavior, losses and thermal validation. Ask engineering for a loaded voltage-speed curve and continuous-duty test results.
4-Phase Dual AFPM Basics
Why choose a dual-rotor configuration?
Two magnet rotors face a central stator. Symmetry may balance net stator axial force, but individual rotors still carry magnetic attraction loads. Check rotor deflection, bearings and air-gap tolerances.
Coreless vs. Cored Stator?
A coreless stator removes stator iron loss and tooth-related cogging, but winding, rotor and mechanical losses remain. A cored design changes the flux path and requires saturation and core-loss analysis. This tool does not select either design.
Do I double poles, flux or turns for two rotors?
No. Enter poles per rotor and actual series turns per phase. Enter the peak fundamental field of the assembled magnetic circuit. This single-stator model counts linked flux once; it does not add two independent generators.
What does four-phase mean in this calculator?
It means four equal sinusoidal phase EMFs at 0°, 90°, 180° and 270° electrical, with a common neutral. Dual refers to two rotors facing one stator, not two electrical phase sets. Other winding connections need a separate circuit model; four phases alone do not establish power, torque ripple or fault tolerance.
Which voltage should I compare with a converter?
For the assumed common-neutral winding, adjacent terminals are 90° apart and have √2 times phase RMS voltage; opposite terminals are 180° apart and have twice phase RMS voltage. Identify the actual terminal pairs, polarity and converter connection. Isolated windings or separate bridges need their own model. Rectified DC depends on load, capacitance, conduction and diode drops and is not calculated here.
Is the magnet remanence Br the correct flux input?
No. Use the peak sinusoidal fundamental in the working air gap from measurement or magnetic analysis. Magnet remanence is a material property; gap length, leakage and the magnetic circuit affect the working field.
Are my inputs uploaded or stored?
Calculation, copying and text export run in your browser without login or AI. The RFQ button opens a draft in your email application; review it before sending.
Sources and calculation boundaries
Published by AFPM Motor. Examples are reproducible calculations, not measured prototype performance or customer test results. Sources checked September 19, 2026. The annulus integration and fixed winding factor are this tool’s screening assumptions, not validated manufacturer data.
| Source | Use on This Page |
|---|---|
| Sathyabama University — Electrical Machine Design, SEE1304 (PDF) | PDF pages 47–48: AC-machine frequency, EMF, winding factor and electrical loading. Supports the base equations, not a validated rating for this topology. |
| MIT OpenCourseWare — 6.685, Permanent Magnet Machines (2013, PDF) | Pages 9–10 distinguish magnet remanence and magnetic-circuit operating conditions. Does not validate the assumed kw=0.95 or a continuous power rating. |
Related tools and next steps
AFPM Generators
Review generator options and the inputs needed for an engineering inquiry.
Coreless Generator Calculator
Estimate performance for coreless axial flux generators.
100 RPM Generator Calculator
Explore low-speed axial flux generator screening.
AFPM Quality and Validation
Plan the evidence needed to verify a prototype under load.
Need a manufacturable generator?
Send the open-circuit estimate, target loaded voltage, rotor OD limit, axial length, and cooling method so engineering can screen whether a dual-rotor AFPM generator is the right architecture.
Inquiry Email
Please include application, peak/continuous torque, speed range, voltage/current limit, outer diameter, axial length, cooling method, quantity, and drawings or reference samples.
Instant Chat
+86 188 5797 1991
Share torque-speed, package, cooling, and sample quantity in the first message.