Hargraves Brushless DC Motors (BLDC) are designed to endure long life applications that under certain conditions exceed 20,000 hours of operation. The Hargraves engineering team took the initiative to improve standard motor designs and manufacturing processes to optimize brushless motor technology with regards to performance, reliability and endurance. We offer our BLDC motor in both a “Short Stack” and a “Long Stack” configuration. The Long Stack motor consists of magnets and windings that are twice the length, and is used for exceptionally high load applications.
Brushless Motor Fundamentals
Brushless motors, as the name implies, do not use brushes for commutation. Instead, they are electronically commutated. The stator consists of stacked steel laminations that are axially cut along the inner periphery. Numerous coils are interconnected to form each winding. An even number of magnetic poles are produced from each of these windings that are distributed over the stator periphery. The rotor is a permanent magnet with alternating magnetic poles built in.
To rotate a DC motor, the windings need to be energized in sequence. The position of the rotor will determine which winding will need to be energized. Unlike brush motors that commutate by mechanical switching, brushless motors position using an electronic sensorless method or by utilizing Hall effect sensors. These sensors are embedded on the stationary part of the motor and monitor the exact position on the rotor’s position. As the rotor’s magnetic poles rotate near the Hall effect sensors, they give a high or low signal that signifies a north or south pole is passing near the sensors. The exact sequence of commutation can be determined from the combination of the three signals the sensors are reading. Each commutation sequence has current entering one of the windings resulting in positive magnetic flow, current exiting a second winding resulting in a negative magnetic flow, and a third winding that would be non-energized. The direction of the magnetic flow would affect the winding’s polarity. The interaction of these changing poles of the magnetic field between the stator and the permanent motor produces the torque that turns the motor’s shaft.
As the requirements for miniature diaphragm pumps to fit in even smaller package envelopes, the motors powering these systems have had to become smaller. These smaller brushless motor sizes will most likely use sensorless commutation methods since Hall effect sensors take up more space. It should be noted that sensorless motors are limited to the initial startup torque they can produce. Brushless DC motor applications that require restarts under a high load will need to utilize Hall effect sensors with an instant start capability. Therefore, to achieve very small motor size, there may need to be a tradeoff on restart capabilities.
Advantages of Hargraves BLDC Motor
Life expectancy – The innovative design and proprietary manufacturing processes contribute to the Hargraves Brushless DC Motor being able to operate under demanding conditions up to 20,000 hours.
Cost – In producing our own motor, Hargraves controls the cost and quality.
Low mass – The Hargraves BLDC motor is a unique compact, space and weight saving design.
Compact, integral commutation circuit - The Hargraves design has a broader voltage control range that facilitates greater operational flexibility. In addition to voltage surge suppression, reverse polarity protection is built in so that the motor cannot be damaged by improperly connecting the lead wires.
Reliable restarts under high loads -The Hargraves BLDC motor is a higher torque design than comparable motors, allowing it to reliably re-start under higher loads than expected.
Broader operating temperature range -The commutation circuit is designed to operate in a 110 ° C maximum ambient temperature, allowing the pump to operate in a broader temperature range. A special high temperature lubricant is used to maintain proper lubrication in bearings at elevated temperatures. Although the standard operating temperature range is 5 – 50 ° C, the BTC pumps with the Hargraves BLDC motor can operate in –30 ° C to 70 ° C range with a 50% pump duty.
Low RFI emission - The removal of the brushes eliminates the introduction of RFI noise into the system circuitry.
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