Brush Motors

Hargraves offers a wide range of cost effective Brush DC Motor technologies that can be recommended for specific miniature diaphragm pump applications. For many fluidic systems, the brush DC motor provides a cost effective solution to power the diaphragm pump.

Brush Motor Fundamentals

The rotor of the motor, also called the armature, is made up of copper windings that will produce a magnetic field when energized with current. The current must pass through carbon brushes that slide over a set of copper surfaces called a commutator, which is mounted on the rotor. The commutator copper surfaces are soldered to the armature coils. Spring loaded carbon brushes slide over the commutator as the motor rotates, coming in contact with different segments of the commutator. The brush and commutator connection makes a sliding switch that energizes particular portions of the armature. This mechanical switching process, called commutation, creates north and south magnetic poles on the rotor that are attracted to or repelled by north and south poles by the permanent magnet on the stator. As the motor turns, the windings are constantly being energized in a different sequence so that the magnetic poles generated by the rotor do not overrun the poles generated in the stator. It's this magnetic attraction and repulsion that causes the rotor to rotate.  

Carbon Brushes

As mentioned above, iron core brush motors typically use carbon brushes to conduct the electrical input from the lead wires to the motor’s commutator. The constant rubbing of the brushes on the commutator causes the brushes to wear down like the lead in a pencil. Brush motors are designed to last from 500 hours to 6,000 hours, depending on the quality of the motor and how it is used. Some applications only require 500 hours of operation life, so a reliable 1,000 hour motor maybe the appropriate choice.

Brush motors that experience frequent on/off cycles per day wear out more quickly, as the brushes experience an electrical arcing upon each start up. The frequent arcing heats up the carbon brushes, causing them to wear more rapidly. A top quality brush motor can be expected to last 3,000 hours with frequent on/off cycles.

Brush motors used in high duty applications with more continuous operation can last longer. A top quality brush motor can run continuously for up to 6,000 hours. It must be stated that few applications allow a pump to run continuously. Frequent starts and stops are the norm. Occasional cycling may lead to motor stall due to carbon dust build up between the brush base and commutator. Tapping the outer housing to clear these deposit from the brush tips can usually restart the motor.

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