Torque to Amp Hour Planning Guide
Why Torque Needs More Inputs
Torque demand is a mechanical value. Amp hour demand is an electrical storage value. The bridge between them is power. This calculator estimates that bridge with practical battery planning inputs. It suits motors, actuators, small vehicles, tools, robotics, and rotating drive projects.
Torque Conversion and Load Factor
The first step is torque conversion. The tool converts the selected unit into newton meters. It then applies a load factor. This factor covers friction, starting drag, gear losses, and real field resistance. A value above one adds extra demand. A value of one keeps the entered torque unchanged.
Speed and Mechanical Power
The second step is speed. Torque alone cannot define energy use. A slow shaft and a fast shaft can need very different power. The calculator changes RPM or radians per second into angular speed. Mechanical power is then torque multiplied by angular speed. More speed or more torque raises power directly.
Electrical Demand
The third step is electrical demand. Motors are not perfect. Controllers, wiring, bearings, gears, heat, and magnetic losses consume energy. Efficiency converts shaft power into required electrical power. Lower efficiency increases current draw. Higher voltage reduces current for the same power, but it does not remove the energy requirement.
Runtime, Duty Cycle, and Reserve
Runtime and duty cycle create the amp hour estimate. Runtime is the total time window. Duty cycle is the active portion of that window. A motor that runs half the time should not be treated like one that runs continuously. The safety reserve then adds extra capacity. Reserve helps cover aging cells, cold weather, voltage sag, and unexpected load spikes.
Using Motor Torque Constant
The torque constant method is useful when motor data is known. Torque constant is listed as newton meters per amp. In that method, current equals torque divided by torque constant. It is often helpful for servo and brushless motor sizing. The power method is better when speed, voltage, and efficiency are the main known values.
Practical Battery Sizing
Use the answer as a sizing estimate, not a final engineering guarantee. Battery chemistry, discharge rate, pack age, controller limits, cooling, cable size, and peak torque can change the real result. A battery may have enough amp hours but still fail to deliver peak current safely. Always compare the calculated current with battery and controller ratings.
Better Input Choices
For better results, enter average working torque for normal running. Use load factor for hard starts and rough conditions. Use realistic efficiency from the motor datasheet. Choose a reserve that matches the risk of stopping early. For critical equipment, test the system under real load. Measurement is the best final check.
Reviewing the Output
The output includes mechanical watts, electrical watts, current, amp hours, watt hours, and capacity margin. CSV export helps save rows for spreadsheets. PDF export gives a compact report for clients, teams, or maintenance logs.
Design Workflow
A good workflow is simple. Start with the required shaft torque. Enter the working speed, not only the no-load speed. Add the expected run time. Then choose a duty cycle that matches the real job. Review the current first. Current affects cable heat, fuse size, switch rating, and controller stress. Review amp hours second. Amp hours estimate how long the pack can support that draw.
Comparing Battery Packs
Watt hours are also important. They make voltage comparisons easier. A 24 volt pack and a 48 volt pack may show different amp hour values for similar energy. Watt hours show the stored energy more directly. This helps compare battery packs across different voltages. Plan with measured data.