Check whether your voltage, RPM, rotor diameter, and magnetic loading can support a 3 kW coreless axial flux generator before you buy magnets, wind coils, or request a custom build.
Published on July 29, 2026; last reviewed on July 29, 2026. The result is deterministic first-pass engineering guidance, not AI output or a substitute for electromagnetic, thermal, and rotor-stress validation.
A 3 kW electrical target needs about 3.33 kW mechanical input at the default 90% efficiency assumption. At 300 RPM, that is about 106 Nm continuous shaft torque.
Evidence: The calculator uses Torque = mechanical watts / angular speed and updates the result from the RPM input.
Coreless AFPM designs have no iron teeth, so rotor diameter, magnet strength, air-gap control, and dual-rotor geometry decide whether the target torque is realistic.
Evidence: The tool estimates torque capacity from rotor OD and air-gap flux density, then reports a torque-margin ratio.
A coreless stator avoids cogging torque, but high current, rotor stress, copper heating, magnet retention, and low-speed torque still need validation.
Evidence: Boundary states flag high torque, high current, low magnetic margin, low flux density, and high rim speed.
| Variable | Formula | Use | Limitation |
|---|---|---|---|
| Mechanical input | kW_mech = 3.0 / 0.90 | Converts the 3 kW electrical target into required shaft power. | 90% is a screening assumption; final efficiency depends on winding, rectifier, cooling, and speed. |
| Required torque | Nm = W_mech / (RPM x 2 x pi / 60) | Shows whether the prime mover can physically turn the generator at 3 kW. | Does not include overload, gust, startup, or bearing friction margin. |
| Electrical current | A = 3000 W / Vdc | Screens conductor size, rectifier losses, connector rating, and thermal load. | Actual phase current depends on winding, rectification, waveform, and controller strategy. |
| Magnetic torque margin | Capacity / required torque | Compares selected rotor OD and flux estimate against a dual-gap coreless AFPM torque heuristic. | Not a substitute for electromagnetic FEA, prototype dyno data, or thermal validation. |
| Rotor rim speed | m/s = pi x diameter(m) x RPM / 60 | Flags when mechanical stress, balance, and magnet retention deserve early review. | Material grade, adhesive, sleeve, and rotor disk design set the real limit. |
| Metric | Result | Decision Use |
|---|---|---|
| Default wind profile | 48 V, 300 RPM, 520 mm OD, 0.62 T | Useful first screen for a low-speed direct-drive generator concept before blade matching. |
| Required shaft torque | About 106 Nm | If the turbine cannot sustain this torque near the target RPM, 3 kW output is not realistic. |
| Electrical current | About 62.5 A at 48 V | Low-voltage systems need heavier conductors and careful rectifier thermal design. |
| Magnetic margin | About 4.5x in the heuristic model | This suggests magnetic loading is not the first bottleneck, but thermal and structural checks still matter. |
| Rotor rim speed | About 8.2 m/s | Low rim speed is mechanically manageable; higher RPM profiles should be checked for retention risk. |
| Application | Useful Input | Likely Fit | Next Action |
|---|---|---|---|
| Small wind turbine | 48-120 V, 150-500 RPM | Best when zero cogging and low cut-in speed matter more than minimum magnet cost. | Compare calculated torque with the blade torque curve at real wind speeds. |
| Micro-hydro | 48-240 V, 500-1800 RPM | Often practical because water flow can provide steadier torque and cooling. | Match generator speed to turbine type, head, flow rate, and rectifier plan. |
| Engine generator | 240-800 V, 1800-3600 RPM | Compact package is possible, but high-speed balancing and overspeed voltage need review. | Define idle, governed speed, overspeed, target DC bus, and cooling airflow. |
| Dyno / test rig | 48-400 V, 500-3000 RPM | Useful for controllable bench loads where smooth torque and simple rectified output are needed. | Confirm coupling torque, load bank rating, duty cycle, and data acquisition needs. |
The stator removes cogging and tooth loss, but copper loss, rectifier loss, eddy current in conductors, and rotor magnet heating can still dominate at 3 kW.
A small change in air gap can reduce effective flux density and erase margin. Rotor flatness, bearing stiffness, and assembly fixtures should be defined before tooling.
A resin-embedded coreless coil has less iron mass to absorb heat. Continuous output needs winding temperature limits, insulation class, cooling method, and duty cycle.
Why does the 3 kW calculator ask for rotor diameter?
At low RPM, torque is the limiting requirement. Rotor outside diameter is a practical proxy for air-gap area, so it helps screen whether the selected magnetic package has enough torque capacity.
What air-gap flux density should I enter?
Use a conservative estimate if you do not have measured data. For early screening, 0.55-0.75 T is a practical placeholder range for strong permanent-magnet axial-flux concepts, but the real value depends on magnet grade, air gap, and rotor geometry.
Is a torque margin above 1.0 enough?
Not by itself. A value above 1.0 only means the simplified magnetic heuristic clears the continuous torque target. Real designs need thermal, voltage, mechanical, tolerance, and duty-cycle margin.
Why does low voltage create a warning?
For the same 3 kW output, lower voltage means higher current. High current increases copper loss, connector size, rectifier heat, and winding packaging difficulty.
Is cogging torque really zero?
A coreless stator removes iron teeth, so cogging torque is effectively eliminated. Bearing friction, seal drag, windage, and electrical loading still create startup and running torque.
Why use a dual-rotor layout?
A dual-rotor coreless AFPM closes the magnetic path across the stator coils and improves usable flux. Single-sided layouts usually leave too much leakage for compact 3 kW designs.
Can this replace detailed electromagnetic design?
No. The calculator is a first-pass feasibility screen. Before sourcing magnets, coils, tooling, or housings, validate winding turns, voltage, losses, thermal rise, rotor stress, and dyno output.
What should I send for an RFQ?
Send target RPM range, voltage or rectifier plan, continuous and peak output, rotor OD limit, axial length, cooling method, enclosure, duty cycle, environment, and prototype quantity.
| Source | Use on This Page |
|---|---|
| Calculation methods on this page | Torque, current, magnetic-margin, and rim-speed formulas are disclosed for reproducibility. |
| Review status | This page was published on July 29, 2026 and last reviewed on July 29, 2026; formulas are deterministic and do not use AI output. |
| OEM validation boundary | Final design requires torque-speed curve, winding, thermal, rotor-stress, and prototype dyno validation. |
Use this when speed is fixed at 100 RPM and you need diameter, torque, pole-count, and weight screening.
Use this when the package diameter is fixed and you need to estimate output inside a small axial-flux envelope.
Review custom generator topology, voltage, rotor, stator, housing, and validation requirements.
Use this when magnet retention, balancing, bonding, coating, or rotor disk tolerances are the main project risk.
Send the calculated torque, target voltage, rotor OD limit, axial length, air-gap assumptions, cooling method, environment, duty cycle, and prototype quantity so engineering can screen whether a coreless AFPM generator is the right architecture.
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