Editing Electric motor (section)

==== Brushless DC ====
{{Main|Brushless DC electric motor}}
Some of the problems of the brushed DC motor are eliminated in the BLDC design. In this motor, the mechanical "rotating switch" or commutator is replaced by an external electronic switch synchronised to the rotor's position. BLDC motors are typically 85%+ efficient, reaching up to 96.5%,<ref name="Nozawa (2009)2">{{cite web|last=Nozawa|first=Tetsuo |date=2009|title=Tokai University Unveils 100W DC Motor with 96% Efficiency|url=http://techon.nikkeibp.co.jp/english/NEWS_EN/20090403/168295/|url-status=live|archive-url=https://web.archive.org/web/20110101131311/http://techon.nikkeibp.co.jp/english/NEWS_EN/20090403/168295/|archive-date=2011-01-01|publisher=Tech-On – Nikkei Electronics}}</ref> while brushed DC motors are typically 75–80% efficient.

The BLDC motor's characteristic trapezoidal [[counter-electromotive force]] (CEMF) waveform is derived partly from the stator windings being evenly distributed, and partly from the placement of the rotor's permanent magnets. Also known as electronically commutated DC or inside-out DC motors, the stator windings of trapezoidal BLDC motors can be single-phase, two-phase or three-phase and use [[Hall effect sensor]]s mounted on their windings for rotor position sensing and low cost [[Closed-loop controller|closed-loop commutator control]].

BLDC motors are commonly used where precise speed control is necessary, as in computer disk drives or video cassette recorders. The spindles within CD, CD-ROM (etc.) drives, and mechanisms within office products, such as fans, laser printers and photocopiers. They have several advantages over conventional motors:

* They are more efficient than AC fans using shaded-pole motors, running much cooler than the AC equivalents. This cool operation leads to much-improved life of the fan's bearings.
* Without a commutator, the life of a BLDC motor can be significantly longer compared to a brushed DC motor with a commutator. Commutation tends to cause electrical and RF noise; without a commutator or brushes, a BLDC motor may be used in electrically sensitive devices like audio equipment or computers.
* The same [[Hall effect]] sensors that provide the commutation can provide a convenient [[tachometer]] signal for closed-loop control (servo-controlled) applications. In fans, the tachometer signal can be used to derive a "fan OK" signal as well as provide running speed feedback.
* The motor can be synchronized to an internal or external clock, providing precise speed control.
* BLDC motors do not spark, making them better suited to environments with volatile chemicals and fuels. Sparking also generates ozone, which can accumulate in poorly ventilated buildings.
* BLDC motors are usually used in small equipment such as computers and are generally used in fans to remove heat.
* They make little noise, which is an advantage in equipment that is affected by vibrations.

Modern BLDC motors range in power from a fraction of a watt to many kilowatts. Larger BLDC motors rated up to about 100&nbsp;kW are used in electric vehicles. They also find use in electric [[model aircraft]].