Permanent Magnet Motors Series Motors and Universal Motors

Electric motors remain to be one of the most important tools to everyday life. They are used in homes, as well as offering numerous industrial applications. There are many types of electric motors, but they are basically classified as AC or DC motors, with DC Motors using battery power or DC Current.

Two common types of electric motors are the Permanent-Magnet Motor and the Universal Motor.

Permanent-Magnet Motors

In a permanent-magnet DC motor, the field coil has been replaced with a permanent magnet, which requires a wound armature. The magnet used is ceramic, using oriented strontium ferrites, although in some cases a rare earth magnet is used. Electric Motors that use rare earth magnets tend to be considerably more expensive.

One of the major advantages of a permanent-magnet DC motor is that it is very small and considerably smaller than a shunt motor. However, despite its size, a permanent-magnet motor still produces high torque at low speed.

In many cases, permanent-magnet motors are used in place of geared motors, but they can not be continuously operated at high torque, because this will cause them to overheat.

Permanent-Magnet Motors also use less power than shunt motors, making them a more efficient option. This type of electric motor can offer some braking functionality by way of using dynamic braking, which involves shorting out the armature. It can also be reversed by reversing the polarity of the armature leads.

While very small and efficient, permanent magnet motors will often loose some magnetism if the temperature drops below zero. High temperatures can also reduce working flux. They are still quite popular for use in both automobiles and maritime applications though, being found in window motors, heaters, blowers, and variable speed water pumps. Permanent-Magnet motors are also popular in winches, fishing reels, trollers, fans, and cordless appliances.

In regards to maintenance, typically the only work involves repairing the brushes, as well as in some as the commutator. It is important to remember that permanent magnet motors are not usually designed for continual use.

Series and Universal Motors

In most cases, a motor is designed for either AC or DC power, but there are some that can use both. They types of electric motors are called Universal Motors, with the series motor being the most popular type of universal motor.

However, not all series motors are universal. In some instances the series motor could be designed for only DC power and not work well or even at all when used with AC power.

Series wound motors allow for both high speed and high torque as soon as it is started. Usually, most universal motors run slower when using AC power, so a resistor is often used to slow it down when on DC power, although this does not dramatically affect torque.

One of the advantages of a series motor is that it is less expensive than other types of motors, which is one of the reasons they are so common in household appliances. They are also the only small electric motor that is capable of achieving a speed greater than 3600 RPMs, usually operating at between 10,000 and 20,000 RPMs.

While some universal motors are in fact quite efficient, they are typically only designed to move in one direction, which actually improves efficiency. When direction is reversed, it causes the way the brushes wear to change, resulting in brushes that wear out much more rapidly.

Series motors do not allow for speed to be well regulated either, but speed can be adjusted by changing the load. In the case of most home appliances that use series motors, the brushes will have to be replaced between 200 and 1200 hours.

No Comments Yet

Add Comment