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How Brushed DC Motors Are Used In Many Industries

The Brushed DC Motor was invented in England by William Sturgeon in 1832. This used basic electric batteries as did the dc motors that were put to commercial use in the US, powering a printing press and some machine tools in 1837. The high cost of electricity from batteries ensured that these applications did not develop.


The first practical commercial use of the dc motor had to wait for the invention of generated DC power. In 1873, Belgian electrical engineer, Zenobe Gramme discovered that a brushed dynamo (with a commutator and wound rotor) connected to another and one was cranked by hand, would make the other dynamo's rotor turn. The brushed DC motor was thus born by accident. Very quickly with the advent of generated DC power becoming available in factories (usually powered by waterwheels), the Gramme motor as it was known came into general use.


The first Gramme motors looked very much like the brushed DC motor today which consisted of the stator, a fixed wire wound coil surrounding the revolving rotor; a number coils wound around a central shaft, a commutator and two carbon brushes that connected the coils in turn as they rotated. The DC energized the stator windings to create a fixed magnetic field, and the two brushes were connected initially in series to the two carbon brushes that connected each rotor coil in a circuit on the rotor in turn via the segmented commutator. The resulting rotation was brought about by the inducted force (Faraday's Law of Induction).

It was soon realized that this basic arrangement when series wound would also work with alternating current (AC) as it would change polarity in both the stator and rotor at the same time and thus the rotational force would still be in the same direction. Thus the series-wound brushed DC motor became known as the Universal Motor. The alternative shunt-wound or parallel-wound dc motor was developed in the late 1800s at the time that distributed AC power supplies became available.


Controls for the brushed DC motor can be simple such as with the simple on/off switch used on much low voltage and low amperage power applications where no speed control is required such as toys and battery powered hand tools and home appliances At low wattages and voltages, there is no significant power surge brought about by the sudden collapse of the magnetic field along with sparking or bursts of radio noise from the switch contacts. Therefore this arrangement is entirely sufficient for the life of the appliance. Of course, with a brushless motor, you rely more on electronic commutators and not mechanical components or brushes.

However, at higher powers and voltages the brushed DC motor requires some means to damp down the on/off switch induced power surge becomes necessary, especially with the advent of sensitive radios and other electronic equipment. You may well have seen the small cylinder moulded around electric equipment's power lead. This is an electrostatic capacitor that provides a power surge damping mechanism. Its primary aim, however, is to reduce contamination of the AC power supply with radio frequency 'noise' and 'spikes.' Small DC motors however routinely have minute capacitors wired across the terminals to reduce sparking by damping down the on/off surge as well as to reduce radio noise.


For speed control of Brushed DC Motor, there are two basic methods used today. The most basic are to reduce the voltage by use of a Wheatstone bridge arrangement or a simpler coil resistor and sliding contact arrangement. The latter dissipates the unused power in the form of heat which is not suitable for anything other than small toys. The other means has come about with the advent of the power transistor in post-war years and this 'chops up' the power electronically into very rapid pulses. This causes the DC motor with its significant rotor momentum, to sense and average DC voltage that is reduced. The speed controllers for higher power applications normally used today are the Silicon Controlled Rectifier (SCR), Thyristor Drive controllers or the Pulse Width Modulation (PWR) driver controllers (also known as 'Chopper Drives')

 


Keywords in the article: Auto Motor,Brushless Motor,Universal Motor,PMDC Motor,Gearbox Motor
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