Conveyor Motor Sizing — AC Induction
For conveyors, size the motor by the power (HP) required at the drive pulley. Determine belt tension and speed, convert to torque and RPM, then select HP, poles (RPM), gearbox ratio, and control (across-the-line, soft-start, or VFD).
Sizing Steps
1) Define the load
Belt speed (ft/min), load per foot (lb/ft), loaded length (ft), pulley diameter (in), friction factor (0.02–0.05 typical), and any elevation force if inclined.
2) Find effective tension
Effective belt force (lbf) = frictional load + any elevation/lift load. This is the linear force the drive must overcome.
3) Convert to torque & RPM
Use pulley diameter to get shaft torque and pulley RPM from belt speed. Then compute HP.
4) Add losses & margin
Account for gearbox efficiency, safety/service factor, and real-world friction. Round up to the nearest standard HP.
Core Formulas
Effective Tension (lbf): Tₑ = (Load_per_ft × Length × Friction_factor) + Elevation_force
Pulley RPM: RPM = (Belt_speed_ft/min × 12) / (π × Pulley_diameter_in)
Shaft Torque (lb·ft): T = (Tₑ × Pulley_diameter_in) / (2 × 12)
Shaft Horsepower: HP_shaft = (T × RPM) / 5252
Motor Horsepower: HP_motor = HP_shaft / (Gear_efficiency × Other_efficiency)
Notes: Use Other_efficiency (e.g., 0.9) for extra losses. Apply a Service Factor (e.g., 1.15) as needed and round up to standard HP.
Worked Example (Horizontal Conveyor)
| Input | Value | Output | Value |
|---|---|---|---|
| Belt speed | 60 ft/min | Pulley RPM | ~57 RPM |
| Load per foot | 10 lb/ft | Effective tension Tₑ | 8 lbf (with Cf=0.04, length=20 ft) |
| Loaded length | 20 ft | Shaft torque | ~1.33 lb·ft (4″ pulley) |
| Friction factor | 0.04 | HP at shaft | ~0.014 HP |
| Elevation force | 0 lbf (flat) | Motor HP (ηgear=0.9, SF=1.15) | Round up → 1/8–1/4 HP |
Interactive Calculator
Selection & Control
Motor & Speed
AC Induction, 4-pole (~1750 RPM) is common. Use 6-pole (~1175 RPM) for quieter/high-torque, 2-pole (~3450 RPM) for compact high-speed.
Conveyors need low output RPM → use a gear reducer sized for torque and service factor.
Control
Across-the-line: fixed speed, simple. Soft-start: reduces inrush/mechanical shock. VFD: adjustable speed, smooth accel, energy savings; optional encoder for vector control.
Environment & Mounting
Enclosures: ODP, TEFC, TENV, washdown, explosion-proof. Mounts: foot, C-face (143/145TC), D-flange. Confirm shaft size & keyway.
What to Specify
Mechanical
Belt speed, load/ft, length, pulley diameter, friction factor, elevation, duty cycle, gearbox ratio/efficiency.
Electrical
Voltage (e.g., 230/460 VAC), phase (3-phase industrial), FLA limits, control method (ATL/Soft-Start/VFD), braking (if needed).
Motor
HP, poles (RPM), NEMA frame (56C, 143TC, 145TC…), enclosure (TEFC/TENV), service factor (≥1.15), NEMA design (B common; C/D for high start torque).