Universal motor

Not all series-wound motors operate well on AC current. Efficiency [ ] Even when used with AC power these types of motors are able to run at a rotation frequency well above that of the mains supply, and because most electric motor properties improve with speed, this means they can be lightweight and powerful. Torque–speed characteristics [ ] Series-wound electric motors respond to increased load by slowing down; the current increases and the torque rises in proportion to the square of the current because the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of the windings and the torque can be very high, and there is a danger of the windings becoming overheated. The counter-EMF aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant, the counter-EMF is zero and the only factor limiting the armature current is the armature resistance. Usually the armature resistance of a motor is low; therefore the current through the armature would be very large when the power is applied. Therefore the need can arise for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-EMF. As the motor rotation builds up, the resistance is gradually cut out. The speed-torque characteristic is an almost perfectly straight line between the sta...

Recent Examples on the Web Electric pressure washers are designed with either a universal motor or an induction motor. — Mike Richard, Men's Health, 17 Oct. 2022 On a universal motor, the power source is linked directly to the blade, providing a lot of power. — Popular Science, 1 Mar. 2021 These examples are programmatically compiled from various online sources to illustrate current usage of the word 'universal motor.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors.

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Universal Motor Working Principle Universal motors work on the same principle as DC series motors, regardless of whether Depending on the supply, a universal motor can be either a DC motor or a single-phase AC motor. With the application of a DC power source to the universal motor, it works just like a DC series motor. In the field winding of the motor, the flow of current produces an electromagnetic field. In addition, the armature conductors also carry a current of the same magnitude. When an AC supply powers a universal motor, it will produce the same unidirectional torque it can produce. The armature winding is connected in series with the field winding, so both of them are in the same phase. Since the polarity of AC constantly changes, the current flowing in the field winding and the armature also reverses simultaneously as the polarity changes. As a result, the magnetic field and armature current are reversed so that the direction of force experienced by armature conductors does not change. applications There are various applications where universal • portable power • washing machines • Vacuum cleaner • small fans • kitchen appliances • Table fans • Sewing machines Why are Universal Motors So Loud? Universal motors much less often used for equipment that is in continuous use as the commutator has because of the commutator, universal motors are typically very noisy. Efficiency Even when used with Advantages A universal motor has the following advantages: • High starti...

The motors which can be used with a single-phase AC source, as well as a DC source of supply and voltages, are called Universal Motor. It is also known as Single Phase Series Motor. A universal motor is a commutation-type motor. If the polarity of the line terminals of a DC series motor is reversed, the motor will continue to run in the same direction. The direction is determined by both field polarity and the direction of current through the armature. As torque is proportional to the flux and the armature current. Let the DC series motor be connected across a single-phase AC supply. Since the same current flows through the field winding and the armature winding. The AC reversal from positive to negative or vice versa will affect the field flux polarity and the current direction through the armature. The direction of the developed torque will remain positive, and the direction of the rotation will be as it was before. The nature of the torque will be pulsating, and the frequency will be twice that of line frequency as shown in the waveform below. Thus, a universal motor can work on both AC and DC. However, a series motor that is mainly designed for DC operation if works on single-phase AC supply suffers from the following drawbacks: • The efficiency becomes low because of hysteresis and eddy current losses. • The power factor is low due to the large reactance of the field and the armature windings. • The sparking at the brushes is in excess. In order to overcome the above ...