March 2014

By definition, adjustable speed drives of any type provide a means of variably changing speed to better match operating requirements. Such drives are available in mechanical, fluid and electrical types. The most common mechanical versions use combinations of belts and sheaves, or chains and sprockets, to adjust speed in set, selectable ratios – 2:1, 4:1, […]

When a current-carrying conductor is placed in a magnetic Field, it experiences a force. Experiment shows that the magnitude of the force depends directly on the current in the wire, and the strength of the magnetic Field, and that the force is greatest when the magnetic Field is perpendicular to the conductor. In the set-up

Actuators are operated in the same way as solenoids. They are used to move mechanisms remotely. Some examples of actuators on a vehicle are, door locks, pre-engaged starter motors and fuel cut off valves. Consider the diagram below. Like a solenoid or relay an actuator has a winding. When current flows around the winding, the

A solenoid is the term used for a heavy duty relay and like a relay acts as a switch saver. Solenoids are used to switch circuits that require a very large current to operate. An example of this type of circuit is the starter circuit. Consider the diagram below. Since the starter circuit requires a lot

This is sometimes known as an ‘either/or’ relay because you can use either one circuit or the other. This type of relay is particularly useful for headlights. Pin number 87A feeds the dipped beam circuit. When the driver selects main beam the relay is energised so the moving contact moves to pin 87 and feeds the

Relays are used extensively in modern vehicles. They can be thought as electro/mechanical switches. They are often used to switch on circuits that require a heavy current e.g. the heated rear windscreen (H.R.W.) circuit. If a relay was not used the contacts inside the HRW switch would need to be quite large to carry the

When the armature rotates a half a revolution ‘A’ is positioned at the south pole “S” and ‘B’ positioned at the north pole “N”. As the magnetic field surrounding ‘A’ is in the anti-clockwise direction the magnetic field would be stronger under ‘A’ and above ‘B’, which would mean that the armature would now rotate

To understand this rule, open your hand, as shown below, with the thumb pointing perpendicular to the index finger, and the index finger perpendicular to the middle finger. Then, point the index finger in the direction of the magnetic flux, and the middle finger in the direction of the current. The direction in which the

An electromagnetic force is a force that acts on a conductor when current flows in the conductor within a magnetic field. It is utilised to operate starter and wiper motors, and the pointers of ammeters, voltmeters, etc. DIRECTION OF ELECTROMAGNETIC FORCE Let’s assume the N and S poles of a magnet are placed near other,

TESTS WHEN ISOLATED 1) VISUAL TESTS: Check that motor frame is mechanically sound.  Remove terminal cover plate and check for ingress of foreign material, moisture etc.  Check for signs of overheating, arcing or burning.  Check ventilation is clear.  2) ELECTRICAL TESTS: Identify windings using a continuity tester.  Measure the resistance of the windings ( 3