Electric Motor Selection for Inclined Conveyors: Loaded Starting and Drive Arrangement Against Runback

Motor selection for an inclined conveyor differs from a horizontal belt in two respects: the power needed to lift the material is added to the calculation, and an arrangement is needed to prevent the loaded belt from running back when power is cut. A standard induction motor does not hold the belt on its own; runback is handled by a backstop on the gearbox or drive shaft, or by a braked drive. Loaded starting is also heavier than on a horizontal belt because of the incline load, and the starting method must be chosen accordingly.

How does the incline change the motor load?

On a horizontal belt the motor mainly overcomes friction. On an inclined belt, the work needed to raise the material to a certain height is added to this. This lifting power is directly proportional to the hourly throughput and the total height; it depends less on belt length than on the vertical difference between the head and tail pulleys.

The calculation below is a hypothetical example. On a belt carrying 100 tonnes per hour up a height of 6 m, the power needed for lifting alone is about (100,000 ÷ 3,600) × 9.81 × 6 ≈ 1.6 kW. Belt, idler and pulley friction, loading of material onto the belt and gearbox losses are added on top of this value. The total power must be found with the belt manufacturer's calculation method; the aim here is to make the share of the incline visible.

• As the incline increases, the height and lifting power increase on a belt of the same length.
• If the material starts to roll back on the incline, capacity falls; this is not a motor problem but a belt and incline design problem.
• When capacity is increased, lifting power increases in the same proportion; on an inclined belt a change in capacity affects motor power more than on a horizontal one.

Runback: what happens when power is cut?

If power fails or the motor is stopped while a loaded inclined belt is running, the weight of the material on the belt pulls it backwards. The belt can accelerate in reverse, material spills back to the lower feed point, the feed hopper overflows and the drive elements are loaded in reverse. On inclined belts this is a serious risk for both operation and occupational safety.

An induction motor produces no holding torque when de-energised. Even with a high gearbox ratio, most helical and bevel gearboxes can be back-driven. Worm gearboxes are known to self-lock at some ratios; however, since this behaviour can change with vibration and wear, it is not accepted as a safety measure on its own.

Arrangements that prevent runback

Applications that require a brake motor need a special motor for this task; it may fall outside the scope of the standard series in HEM Motor's 2026 catalogue. Ask us with the nameplate and application details. A standard motor can be used as the drive motor in arrangements where runback is solved with a backstop. The selection and sizing of the safety devices are the responsibility of the machine manufacturer.

The critical step of a motor replacement on a backstop drive: direction of rotation

On a drive with a backstop, if the motor is connected in the wrong direction it tries to start against the lock. In this case the motor does not turn and draws high current; the backstop, gearbox or coupling may be damaged. That is why the first start after replacement needs special care:

• Before the replacement, photograph the phase sequence and terminal connection of the old motor.
• If possible, check the new motor's direction of rotation without connecting the coupling or belt, unloaded and with a very short start.
• If the direction is correct, complete the connection; if it is wrong, swap two phases at the terminal board.
• If the direction is to be tried with the coupling connected, the start must be very short and cut immediately if the motor hums.

Loaded starting and starting method

When an inclined belt stops, material remains on it. At start-up the motor must cover the incline load in addition to friction and inertia; this load is at its full value from the moment of starting. That is why a starting arrangement that works without problems on a horizontal belt may be insufficient on an inclined belt.

• Direct-on-line starting: Gives the highest starting torque. It creates sudden tension in the belt and pulleys; on long belts the belt splices are stressed.
• Star-delta: Reduces starting torque to about one third. On a loaded inclined belt the risk of the motor failing to reach sufficient speed in the star stage is high; if the belt will start fully loaded this method must be evaluated carefully.
• Frequency inverter: Provides starting and stopping with a controlled ramp. When stopping, the drive decelerates the belt along a ramp; however, when power is cut the drive also drops out, so a runback measure is still needed. Our three-phase series are suitable for speed control with a frequency inverter; for long periods of full-torque operation at low speed an external fan may be required, and if the cable between drive and motor is long a dv/dt or sine filter is considered; these conditions are stated with the order.

On an inclined belt, the torque needed at start-up after a stop should be evaluated together with the motor's rated torque. Rated torque values are on the product pages and in the torque table.

Example models for inclined belts

4-pole cast iron examples working with a gearbox and backstop. Power is selected according to capacity, height, belt length and the loaded-start condition:

• 132S-4 cast iron frame: 5.5 kW, 4 poles, 1,460 rpm, 400/690 V, IEC 132S, rated torque 36 Nm.
• 160M-4 cast iron frame: 11 kW, 4 poles, 1,465 rpm, 400/690 V, IEC 160M, rated torque 71.7 Nm.
• 160L-4 cast iron frame: 15 kW, 4 poles, 1,465 rpm, 400/690 V, IEC 160L, rated torque 97.8 Nm.

Review suitable HEM Motor models and current prices on the buy electric motors page. General information on conveyor drives is on the conveyor belt electric motors page. For motors to be connected to a gearbox by flange, the mounting arrangement is offered according to the frame and the flange size is confirmed with the order.

Conclusion and what is needed for a quotation

On an inclined conveyor, add the lifting height to the power calculation, prevent runback with a backstop or braked drive, and choose the starting method for loaded starting. On a backstop drive, do not run the belt after a motor replacement without checking the direction of rotation. For a quotation we need the capacity, belt length and incline (or height difference), belt speed, gearbox nameplate, type of runback measure, starting method, current motor nameplate and environmental conditions.

You can see suitable models and current prices in our online sales section. Send the nameplate photo, speed and mounting details of your current motor through the send nameplate page and request a quotation for the suitable model. For questions about the drive arrangement, write to us via our contact page.

Frequently Asked Questions

Does the gearbox hold an inclined belt against runback?

Most helical and bevel gearboxes can turn in reverse. The self-locking behaviour of a worm gearbox is not a reliable measure; a backstop or brake is needed.

Why does the motor on a backstop conveyor hum and not start?

The motor is most likely connected in reverse and pushing against the lock. Stop the motor immediately, swap two phases at the terminal board and check the direction with a short start.

Does a frequency inverter prevent runback?

In a normal stop it decelerates along a ramp, but when power is cut the drive does not work either. The runback measure must be independent of the drive.

Can star-delta starting be used on an inclined belt?

It can be used if the belt starts empty. On a loaded inclined belt the starting torque drops to one third, so the motor may stall in star; this should be stated with the order.