48V Axial Flux Motor
Estimate 48V axial flux motor current and torque. Verify system limits with your supplier.
By AFPM Motor · ·
Engineering Reality of 48V Systems
Lower voltage raises current for a given power and puts more attention on the battery, inverter, wiring, and thermal path. A nominal voltage alone does not establish a safety classification or remove application-specific compliance requirements.
1. The I²R Heating Penalty (Continuous vs. Peak)
For a 10kW shaft-power example, assuming 90% combined inverter and motor efficiency, the DC input is about 11.1kW: approximately 231A at 48V, 116A at 96V, or 27.8A at 400V. At the same power and conductor resistance, doubling current makes that conductor's I²R loss four times higher. This is a like-for-like conductor comparison, not a prediction that every 48V motor system loses four times as much heat. There is no universal continuous-power ceiling for 48V axial flux motors; duty cycle, winding, cooling, speed, ambient temperature, and controller limits determine the rating.
For another worked voltage comparison, see the 10kW axial flux motor sizing guide.
When comparing a continuous or S1 rating with a peak rating, check the cited cooling, ambient temperature, speed, duration, and temperature limits. A short-time figure does not establish continuous capability.
Compare the DC Bus Current at 10kW Shaft Output
| Assumed DC bus voltage | Estimated DC input current | Interpretation |
|---|---|---|
| 48 V | 231.5 A | Highest current in this comparison; check battery, inverter, DC conductors, and connectors. |
| 96 V | 115.7 A | About half the 48 V DC current at the same assumed output and efficiency. |
| 400 V | 27.8 A | Lower DC current in this idealized comparison; introduces a different safety and compliance design scope. |
Calculation: 10,000W ÷ (bus voltage × 0.90). Use the actual loaded voltage and supplier efficiency map for a design decision.
2. Regulatory Boundary: A 48V Label Is Not a Safety Approval
Do not treat a 48V nominal rating as a blanket SELV classification or as an exemption from vehicle safety requirements. The applicable tests depend on the maximum working voltage, circuit connections, vehicle category, and regulation series. UN Regulation No. 100 sets approval provisions for electric powertrains. Requirements and tests depend on the full vehicle and electrical design. Check the complete system with the approval authority or a qualified compliance engineer before making a certification claim.
Reference texts: UN Regulation No. 100, Revision 4, Amendment 1 · ISO 6469-3:2021
3. Component Selection Bottlenecks
DC bus current and motor phase current are different values. This screen calculates only the DC side; request the controller and motor current limits separately.
| Component | What to verify | Mitigation |
|---|---|---|
| Inverter/Controller | Verify continuous and peak DC input current separately from motor phase RMS current, along with temperature derating. | Match the controller current map and cooling to the full duty cycle and loaded bus voltage. |
| Battery and BMS | Check continuous and transient discharge limits at the minimum loaded voltage, including cell, BMS, and pack temperature limits. | Validate the cell configuration and BMS against a measured or modeled duty-cycle current profile. |
| DC and phase conductors | DC bus current is not motor phase current; cable ampacity also depends on conductor length, insulation, routing, and temperature. | Size each cable set from its own current waveform, voltage-drop target, installation rules, and connector ratings. |
4. The Form Factor Dilemma
High DC current affects the battery, inverter, bus conductors, and thermal design, but it does not impose one fixed motor diameter or winding solution. The usable envelope depends on torque and speed, electromagnetic loading, winding layout, cooling path, duty cycle, and packaging constraints. Ask the supplier to size the motor and inverter together and provide continuous and peak ratings with their test conditions. For wider motor topology and package trade-offs, read our axial flux electric motor overview.
Risk Management
Risk: Voltage Sag
Trigger: Battery, busbar, connector, or cable resistance reduces DC bus voltage under load.
Fix: Use the minimum loaded voltage from the pack model or measurement and confirm inverter undervoltage behavior.
Risk: Thermal Overload
Trigger: A short-duration peak rating is used as if it were a continuous S1 rating, or cooling/ambient conditions differ from the test.
Fix: Request continuous and peak test conditions, temperature limits, cooling flow, and derating curves for the motor and inverter.
FAQ
What is the maximum practical power for a 48V motor?
There is no universal ceiling. For one model-specific example, Saietta lists 12kW continuous S1 for its AFT140i 48V; other designs have different cooling, winding, speed, and test conditions. Compare supplier continuous and peak ratings on the same duty basis.
How much DC current does a 10kW shaft output need?
At an illustrative 90% DC-to-shaft efficiency, about 231A at 48V, 116A at 96V, or 27.8A at 400V. Use the actual loaded bus voltage and the motor/inverter efficiency map; the calculator estimates DC bus current only.
Does a nominal 48V system avoid high-voltage safety requirements?
Do not infer a safety classification or blanket exemption from nominal voltage alone. Maximum working voltage, connected AC/DC circuits, vehicle category, and the applicable regulation series all matter. Get a compliance review for the complete system.
Can I use a 48V motor with a 72V controller?
Not without written confirmation for the exact motor and controller. Check maximum operating voltage, inverter and capacitor ratings, battery limits, insulation, overspeed, thermal limits, and warranty. A 48V product label does not establish 72V compatibility, and speed does not universally rise by a fixed percentage.
Which current number should I use to select the inverter and cables?
Use DC bus current for the battery-side components and supplier phase RMS/peak current for the motor-side inverter outputs and phase conductors. The two are not interchangeable; confirm the current map, duty cycle, temperature derating, and cable installation conditions.
What should I send an OEM for a useful 48V feasibility review?
Provide continuous and peak shaft power or torque, speed range, duty cycle, loaded DC voltage range, ambient temperature, cooling method, package limits, and target quantity. Ask for the winding/current map, efficiency map, thermal limits, and test conditions in return.
Need an engineering review?
Share your duty cycle, loaded voltage, and cooling limits for a system-level feasibility discussion.
Evidence, Assumptions & Validation
Sources checked 30 September 2026. Product ratings below apply to the cited model only; they are not a market-wide benchmark.
- UN Regulation No. 100, Revision 4, Amendment 1: Vehicle approval requirements are scoped to covered vehicle categories and defined electrical conditions. Confirm the current text and market applicability for the actual system.
- ISO 6469-3:2021: Electrical-safety requirements for voltage-class-B propulsion and connected auxiliary circuits in electrically propelled road vehicles; this does not establish requirements for every AGV, marine, or off-road application.
- Saietta AFT140i product specifications: Lists 12kW continuous S1 (30+ minutes), 48V nominal, a 60V maximum operating voltage. This is a model-specific example, not a market-wide rating; request current data and test conditions from the supplier.
- Calculator method: DC input current = shaft power ÷ (entered DC bus voltage × assumed 90% DC-to-shaft efficiency). Torque = shaft power ÷ angular speed. The efficiency is an illustrative input, not a claim about typical performance; validate with a supplier efficiency map and the minimum loaded voltage.
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