How is the motor power determined for a feed mixer?

The motor power of a feed mixer is not determined by tub volume alone; even at the same volume, the density of the ration, the fibrous material in it and whether the machine is started while full all change the requirement. The most reliable starting point is the power given by the machine builder for that volume and type; the motor should not be reduced below it.

Differences by machine type

In vertical auger mixers, a single large screw lifts the material and lets it fall at the sides; when straw is loaded as bales, the auger knives also do cutting work and the load increases. In horizontal mixers, paddle or ribbon shafts mix along the tub; with powdery rations such as flour and bran the load is smoother. In both types the motor is usually 1500 rpm and drives through a gearbox.

Conditions that increase power

• Loading straw or silage into the tub first, then concentrate
• The mix becoming heavier with molasses and liquid additives
• Stopping the machine while completely full and starting it again
• Knives becoming blunt and cutting resistance increasing

If these conditions are frequent, especially when full starts occur, the next power rating up can be considered. However, starting difficulty may also stem from the starting method; the decision on this depends on the motor nameplate, the manufacturer’s documentation and the assessment of qualified electrical personnel.

Deciding by measuring the existing motor

If the machine is already running, measuring the load current with a clamp meter on the heaviest ration is the most concrete data. If the current is close to the nameplate value, the motor is working at its limit; if it is well below, there is no need to increase power. The motor calculation tool can be used to find the approximate shaft power.

For stationary mixers the feed mixer motors page gives details; once the right power is known, a model can be chosen from the three-phase motor shop to suit the gearbox input.