Electric Motor Selection for Seed Cleaning and Grading Machines

There is no single "seed cleaner motor" in a seed cleaning and grading machine; the machine consists of several motors, each carrying a different load: the drive that shakes the sieve box, the air separation fan, the indented cylinder, the feeder and the elevator. For a correct selection, first identify which motor performs which task, then keep the old motor's speed and mounting for each one. Seed processing adds one more criterion: handling the seed without breaking or damaging it, which requires care regarding speed and starting.

Motors on a seed grading line and their load characteristics

A seed cleaning line separates the product step by step according to differences in size, weight and shape. The motor of each stage carries a different load:

This table is used to determine which group the motor to be replaced belongs to. For example, even if the indented cylinder motor and the fan motor have the same power, they cannot replace each other; one turns slowly through a gearbox, the other runs at high speed directly or via a belt.

Protecting the seed: why is speed critical?

With feed or milling grain, a small amount of kernel breakage is acceptable. With seed, however, broken or cracked kernels lower the germination rate. That is why in a seed cleaner a motor speed that is "a little faster" is not an advantage:

• If the indented cylinder turns too fast, kernels fall out of the pockets too early or are damaged by impact; separation deteriorates.
• Elevator buckets at high speed throw the kernels hard against the discharge spout.
• If sieve oscillation increases, the kernel's residence time on the sieve is shortened and cleaning quality falls.

When replacing, keep the old motor's synchronous speed. A difference of a few rpm between the rated speed on the nameplate and that of the new motor is normal; a different number of poles, however, clearly changes the machine speed.

Speed adjustment for different products

If different seeds such as wheat, chickpeas or sunflower are processed on the same cleaner, the manufacturer usually provides pulley sets or adjustment dampers. Speed can also be adjusted with an inverter: HEM Motor's three-phase series are suitable for speed control with a frequency inverter; for long periods at low speed with full torque an external fan may be required, and if the inverter-motor cable is long a dv/dt or sine filter is considered. State these conditions with the order. For details see the question on inverter operation.

Supply and frame selection on mobile seed cleaners

Some seed cleaning machines are mobile units mounted on trailers and moved from village to village. Two issues stand out with these units:

• Power source: If there is no mains supply on site, a generator is used. The combined starting current of the motors strains the generator's capacity; switching on large motors one after another reduces voltage drop. Check that the voltage on the motor nameplate (such as 230/400 V Δ/Y) matches the supply on site.
• Weight and vibration: On a transported machine, the aluminium frame is preferred for its lightness. On units subject to road vibration and frequent dismantling, the rigidity of the cast iron frame may come to the fore. Both frames have IP55 protection and class F insulation.

On a unit working outdoors, a canopy that protects the motor from rain and direct sun reduces water ingress into the terminal box and overheating. For mobile machines that stand idle for long periods, the recommendations in our article on storing spare motors can also be applied to protect the motor against moisture.

Dust, seed treatment and cleaning

The dust from seed cleaning is fine and abrasive; pieces of husk and awn build up on the motor's fan cover. Keeping the cooling path clear is the simplest measure for motor life. Some lines have a seed treatment unit after cleaning; for motors in an area with heavy treatment vapour, state the ambient conditions with the order. IP55 protects against splashing water, but chemical vapour and washdown conditions may exceed the scope of a standard motor.

Example models for seed cleaner units

The aluminium frame models below are examples of the power and speed classes frequently seen on seed grading lines. The exact selection is made from the old motor's nameplate or the machine manufacturer's data. You can review suitable HEM Motor models and current prices on the buy electric motors page.

• 90S-6: 0.75 kW, 6-pole, 935 rpm, aluminium, IEC 90S, 230/400 V (Δ/Y). For slow drives such as an indented cylinder with gearbox, if the old motor is also 6-pole.
• 90L-4: 1.5 kW, 4-pole, 1,445 rpm, aluminium, IEC 90L, 230/400 V (Δ/Y). For eccentric sieve drives and elevators.
• 100L1-4: 2.2 kW, 4-pole, 1,450 rpm, aluminium, IEC 100L, 230/400 V (Δ/Y). For larger sieve boxes and feed screws.
• 90L-2: 2.2 kW, 2-pole, 2,895 rpm, aluminium, IEC 90L, 230/400 V (Δ/Y). For direct-coupled aspiration fans.

Other options for agricultural equipment are listed on the agricultural machinery motors page. Mounting arrangements are offered according to the frame and the flange size is confirmed with the order.

Hypothetical example: a seed cleaner with rising kernel breakage

This example is not a real application. Suppose the indented cylinder motor on a cooperative's seed cleaner has failed and has been replaced with a motor of the same power but with 4 poles. In the following batches the broken kernel rate rises and the cylinder separation weakens. When the old motor's nameplate is examined, it turns out to have been 6-pole; with the same gearbox, the cylinder speed has increased by about fifty percent. The solution is to return to a 6-pole motor or to change the gearbox ratio according to the machine manufacturer's data. The problem here is not power but speed.

Summary and information to prepare for a quote

On a seed cleaning line, assess each motor according to its own task: base the decision on speed for sieves and indented cylinders, on the impeller-speed relationship for fans, and on the starting load for elevators and screw conveyors. On mobile units, consider the power source and frame choice separately. When requesting a quote, send the following:

• Which unit the motor to be replaced works on, and a nameplate photo
• Mounting arrangement, pulley or gearbox connection
• Supply: mains or generator; voltage value
• Environment: outdoors, dust, treatment vapour

You can see suitable models and current prices in our online store. Share the nameplate photo, speed and mounting details of your existing motor via the nameplate submission page and request a quote for a suitable model. For other questions, contact us.

Frequently Asked Questions

Can the seed cleaner's fan motor and sieve motor be the same model?

Even if their power is the same, usually not. The fan generally runs at high 2-pole speed, while the sieve drive uses a 4-pole motor with a pulley; each motor is selected according to its own speed.

If I replace the indented cylinder motor with a faster one, will capacity increase?

No, separation quality deteriorates and kernel breakage may increase. The cylinder speed is a design value.

What should be watched when a mobile seed cleaner runs on a generator?

Switching on the motors one after another prevents starting currents from overlapping. The generator voltage must suit the connection on the motor nameplate.

Can a standard motor be used on a seed treatment unit?

It depends on the vapour and washdown conditions in the environment. If there are conditions beyond the limits of IP55 and class F insulation, state them with the order.