Electronic Motors Inside Everywhere of Household Appliances

Most labour-saving household appliances contain an electric motor of some description. They are the workhorse of these appliances and most of them are capable of coping with the work loads inflicted upon them. However, some motors, either through poor design or as a result of manufacturers’ cost limitations, are inadequate for the job they are required to do. Adequate or not, at some point it is almost inevitable that they will fail or simply wear out. To delay this, use the appliance with some care and attention, be aware of its limitations and carry out regular inspection and servicing. This will prevent small problems escalating into major ones

Not only do the sizes of motors vary greatly between products, so too do the ways in which they work. To diagnose faults successfully and service or repair appliances, a working knowledge of motors is essential. The following provide a basic introduction to the various types, a description of how they work, the appliances in which each may be found and their particular advantages and drawbacks. Specific problems can be found on individual appliances.

Three types of motors are used in the larger mains powered appliances: brush motors, induction motors (capacitor start), and induction motors (shaded-pole). Although any one of these may also be used in a hairdryer, it is more likely that a smaller, fourth type — the DC (direct current) powered permanent magnet motor — will be used. Electric shavers are also covered in a separate section.

Brush motor

This is by far the commonest type of motor used in mains powered household appliances. There are many variations in size, power and speed. It is easily identified by its shape: its length is greater than its width. Brush motors are used in upright and cylinder vacuum cleaners, food mixers, electric drills, hedge trimmers, strummers and spin dryers.

The brush motor consists of two sets of electromagnets: an outer fixed set called the field coil, and an inner free set called the armature. The armature is made up of many separate windings, configured in such a way that power is supplied to only one set of windings at a time. The corresponding movement induced in the armature continuously brings a new set of windings into circuit, while the previous winding circuit is broken. The windings are continuously out of synchronization thus inducing continuous rotation of the armature when power is supplied. Reversing is achieved simply by reversing the power flow through the field coil winding.

Due to the switching device, called the commutator, a brush motor can be used either with alternating current (AC) from the mains or direct current (DC) from a battery. The commutator is made up of many copper segments. Each segment is connected to a winding in the armature and is supplied with electricity through two stationary pieces of graphite called brushes. These are pushed on to the commutator by springs.

When power is applied to the motor, current flows to the field coil and through the brushes to the commutator. This magnetizes the armature coils, inducing rotation. As the armature rotates, the next two segments of the commutator come into contact with the brushes. This operation is repeated many times a second.

Speed is often controlled by pulsing the power, that is, when the pulse is slowed, the motor slows. This is not quite as, straightforward as it may seem because the pulse has to be smooth to eliminate any jerkiness at low speeds. This is achieved by a speed control module. Many appliances have variable speed control.

The induction motor

The induction motor is quite simple and uses the absolute basic principles of electricity. Its apparent complexity stems from the need to use extra windings to control its speed. Although modem electronics have allowed for variable control, only the basics of induction motors used without module control are covered here.

Induction motors — capacitor start

Induction motors can only operate on alternating current (AC), and are technically called asynchronous induction motors. Single-phase household induction motors consist of two main items: an outer wound coil, called a stator, and a rotatable core, called the rotor, made of high-grade cast aluminium with internal metal lamination, which are slightly skewed to aid torque for starting purposes. The rotor is isolated from the windings and receives no power at all.

The simplest stator consists of two sets of windings at 180 degrees to one another. Motion is induced by placing one set of the windings 90 degrees out of phase with the other. This is done by introducing a delay in the current flow to one winding using a relay or, more usually, a capacitor, the rating of which is matched to the windings; the rating is given in microfarads (mF) on its casing. A rotating magnetic field is created causing the rotor to accelerate to working speed, when the start windings, as they are known, can be switched out if required. Reversal of the motor is achieved simply by reversal of current flow through the starting winding or the run winding, but not both.

Speed

When a motor is supplied with mains voltage (now a nominal 230 volts) at 50Hz its speed is a function of the phase cycle (50 cycles per second) and the number of poles in the unit. A two-pole motor mimics the phase cycle and rotates at 50 revolutions per second, that is, 3,000rpm, a four pole motor rotates at 1,500rpm, an eight pole motor rotates at 750rpm, and a 16 pole motor rotates at 375rpm. As variable speed motors require complex stator windings and are expensive, it is wise to check promptly and rectify any faults with motors immediately. A loose motor block connection may allow power to one winding only and cause overheating and the failure of the whole motor. A faulty capacitor or the malfunction of a selector switch or internal thermal overload cut-out (TOC) can also have the same result.

Inspection

When checking for faults always isolate the appliance by switching off at the wall socket and removing the plug. However, the capacitor(s) will still contain a charge. This must be discharged by using the shaft of an electrically insulated screwdriver to ’short’ the terminals of the capacitor, ensuring that you are in contact with only the insulated handle. It is not safe to proceed further until this has been done.

If the stator windings of an induction motor are faulty, the motor may continue to run, although it may appear to be sluggish and tend to get extremely hot even when it is used only for a short time. Therefore, if you have been running the machine to determine the fault, proceed with care as the motor will remain hot for some time. If the windings are faulty the unit will have to be replaced.

Possibly related posts: (automatically generated)
Electronic Motors Inside Everywhere of Household Appliances

• Electronic Appliances Cables Organizing and Safety Tips
• Coffee filters
• Home Appliance Tips: Cleaners and powertools part 1
• Cylinder cleaners
• Appliance Tips, Defrosting the Fridge, Cleaning the Kettle, Cleaning an Iron
• Electronic Motors Inside Everywhere of Household Appliances continue...
• Gas Clothes Dryer and Electronic Dryer, Household Appliance Clothes Dryer how it Works
• Household Appliances Heating up Elements In
• Efficient Home Power tools continue…
• Why not have Steam cleaners