Brushless Dc Motor Uses Slotless Design

Brushless dc motor uses slotless design The brushless, slotless dc motors from Xtreme Energy, St. Petersburg, have all the advantages of slotless, brushless technology combined with a proprietary coil winding configuration that reduces current losses. The motor is also autoclavable, so it can be used in medical equipment that needs sterilizing between uses. Being brushless, there are no mechanical contacts between the voltage source and

the motor's rotating components, which reduces maintenance and potential for failure. It also reduces the electromagnetic and radio frequency interference (EMI and RFI). The slotless design uses a basket winding inserted into a ring lamination with no teeth or slots. Therefore, rotation is smooth with virtually no cogging. The motor weighs less, has lower magnetic losses, and produces less heat. Compared to slotted, brushless motors which are 30 to 70% efficient, Xtreme's are up to 95% efficient. They do not need a cooling fan and noise levels are low. They are also capable of speeds over 100,000 rpm, while other brushless, slotted dc motors can go no higher than 30,000 rpm. And while costs for other brushless, slotted motors range from $200 to $2,500, Xtreme's are available for $85 to $850, depending on size and quantities.

DC Motor Repair

With literally decades of experience, DC equipment repair has become a specialty at Jenkins Electric. We service a wide variety of industrial customers and also provide services other motor repair centers. DC motors and generators introduce additional complexity into the repair process. The additio of (1) a commutator with brushes, and (2) rotating armature coils subjected to centrifuga force are factors not involved in typical AC repair.

The following procedures and tests are used at Jenkins Electric to ensure top-quality DC machin repair: Conductive carbon dust left by worn brushes is cleaned from the armature; then each commutator is checked for grounds and bar-to-bar shorts with detailed electrical testing. Technicians repair most commutator problems in-house. For severely damaged or non-repairable commutators, we have several excellent sources for fast delivery of custom manufactured replacements. Coils are manufactured in-house to assure proper fit. This eliminates constant bending and shaping during installation which can damage coil insulation. Proper banding is critical in DC repair. This ensures that windings are held in position during high-speed operation. Field coils are checked using voltage drop testing. Bad fields and interpoles are rewound in our shop on custom-made forms. TIG welding is available to eliminate soldered joints where design dictates. All commutators at Jenkins Electric are turned, undercut, and chamfered to provide the best possible surface for brush contact. For corrosive or other severe duty environments, commutator platinum plating is available to extend wear life. Neutral setting adjustments are made during final machine testing to insure proper operation. Rebuilding DC armatures for critical applications

Elevator maintenance companies are very particular about who services their elevator motors - and for good reason. Jenkins Electric repairs a majority of these motors for all elevator companies in this region. _______________________

A technician installs form coils in the armature with coil leads fitted to the commutator (left). Coil leads are then soldered or welded int place.

After multiple dip and bake varnish cycles, the commutator is turned in a lathe to remove worn brush tracks and other surface irregularities

Mica insulation between each commutator segment is undercut using a special, high-speed saw

Each commutator segment is hand-chamfered as "fine tuning" for smooth, trouble-free brush contact

Miniature Dc Motor Achieves High Speeds at Low Temperatures A 6-mm-diam brushless motor is reportedly the world's smallest electronically commutated dc motor with magnetic

sensors. The component turns at up to 100,000 rpm and weighs only 2.8 g. Developed and manufactured by Maxon Motor AG (Sachseln, Switzerland), the unit is suited for use in infusion pumps and endoscopy applications. The motor has a power rating of 1.2 W and operates at a low temperature. At a noload speed of 80,000 rpm, the motor reaches a housing temperature of only 52°C. Constant performance can be achieved up to a maximum temperature of 125°C. Magnetic Hall sensors supply information on rotor position and help the drive achieve precision and a good start-up response. The nominal voltage is 9 V dc. As with other dc motors, the operating voltage varies within a wide range. The maximum continuous current is 500 mA, and maximum continuous torque is 0.260 mN•m. The company is currently working on a range of 6-mm planetary gearheads for applications requiring higher torque at lower speeds. Suitable electronics are also available.

A brushless DC motor is an electric motor that operates like a DC motor, but with the roles of the rotor and stator reversed. The rotor consists of a set of permanent magnets and the stator consists of electromagnets. The motor has no brushes and no commutator in the traditional sense, but the role of the commutator is played by an electronic circuit, that switches the current to the different stator coils at the appropriate times. There exist integrated circuits specially designed for this purpose. Many brushless DC motors contain Hall effect sensors, so the electronic circuit knows the rotor position and can switch the current in the stator coils accordingly. Some brushless DC drive circuits use the back EMF in the undriven coils to sense the rotor position, so they do not need the Hall effect sensors. The advantages of brushless DC motors over conventional DC motors are high reliability, no production of sparks and no production of electromagnetic interference. The disadvantage is higher cost due to the complex electronics.

Brushless DC Motors Brushless DC motors are refered to by many aliases: brushless permanent magnet, permanent magnet ac motors, permanent magnet synchronous motors ect. The confusion arises because a brushless dc motor does not directly operate off a dc voltage source. However, as we shall see, the basic principle of operation is similar to a dc motor. A brushless dc motor has a rotor with permanent magnets and a stator with windings. It is essentially a dc motor turned inside out. The brushes and commutator have been eliminated and the windings are connected to the control electronics. The control electronics replace the function of the commutator and energize the proper winding. As shown in the animation the winding are energized in a pattern which rotates around the stator. The energized stator winding leads the rotor magnet, and switches just as the rotor aligns with the stator. There are no sparks, which is one advantage of the bldc motor. The brushes of a dc motor have several limitations; brush life, brush residue, maximum speed, and electrical noise. BLDC motors are potentially cleaner, faster, more efficient, less noisy and more reliable. However, BLDC motors require electronic control.

Full Step Stepper Motor This animation demonstrates the principle for a stepper motor using full step commutation. The rotor of a permanent magnet stepper motor consists of permanent magnets and the stator has two pairs of windings. Just as the rotor aligns with one of the stator poles, the second phase is energized. The two phases alternate on and off and also reverse polarity. There are four steps. One phase lags the other phase by one step. This is eqivilent to one forth of an electical cycle or 90°. This stepper motor is very simplified. The rotor of a real stepper motor usually has many poles. The animation has only ten poles, however a real stepper motor might have a hundred. These are formed using a single magnet mounted inline with the rotor axis and two pole peices with many teeth. The teeth are stagered to produce many poles. The stator poles of a real stepper motor also has many teeth. The teeth are arranged so that the two phases are still 90° out of phase. This stepper motor uses permanent magnets. Some stepper motors do not have magnets and instead use the basic principles of a switched reluctance motor. The stator is similar but the rotor is composed of a iron laminates.

Half Step Stepper Motor This animation shows the stepping pattern for a half-step stepper motor. The commutation sequence for a half-step stepper motor has eight steps instead of four. The main difference is that the second phase is turned on before the first phase is turned off. Thus,

sometimes both phases are energized at the same time. During the half-steps the rotor is held in between the two full-step positions. A half-step motor has twice the resolution of a full step motor. It is very popular for this reason.

Switched Reluctance Motors A switched reluctance or variable reluctance motor does not contain any permanent magnets. The stator is similar to a brushless dc motor. However, the rotor consists only of iron laminates. The iron rotor is attracted to the energized stator pole. The polarity of the stator pole does not matter. Torque is produced as a result of the attraction between the electromagnet and the iron rotor. The rotor forms a magnetic circuit with the energized stator pole. The reluctance of a magnetic circuit is the magnetic equivilent to the resistance of a electric circuit. The reluctance of the magnetic circuit decreases as the rotor aligns with the stator pole. When the rotor is inline with the stator the gap between the rotor and stator is very small. At this point the reluctance is at a minimum. This is where the name “Switched Reluctance” comes from. The inductance of the energized winding also varies as the rotor rotates. When the rotor is out of alignment, the inductance is very low, and the current will increase rapidly. When the rotor is aligned with the stator, the inductance will be very large and the slope decreases. This is one of the difficulties in driving a switched reluctance motor.