CP Fitters' Phase 2 Apprenticeship Training

A bridge wave rectifier utilises at least four diodes to control the flow of the current produced by the geneator. If we look at the wiring diagram for a simple bridge wave rectifier we can see that the input is coming in between two sets of diode pairs with anode to cathode configuration. this ensures that regardless of the direction of flow from the alternating input whether its negative or positive, the incoming current can only flow in one direction.

Contributor: Lorcan McGivney, CP Fitters, January to May, 2012.

Coolant is the liquid that absorbs heat from the engine and then dissipates it through the radiator. It can also dissipated through the cab heater in the drivning compartment of the vehicle.

The main component of coolant is water, for the following reasons:

• Water is (almost) free, easily available and non-volatile.
• Water has a very high specific heat capacity - it takes a relatively large amount of energy to raise its temperature by 1^oC. You can read more about the specific heat capacity of water here.

Pure water as coolant does have the following disadvantages:

• Water boils at 100^oC, and turns to steam.
• Water freezes at 0^oC, crystallises and expands. This will cause it to damage whatever system it is enclosed in.
• Water causes corrosion.

Water as coolant does have big advantages, that is why we use it, but we must add things to it, and do things to the environment in which we store and work it:

• Water boils at 100^oC and turns to steam. This temperature is below what many modern engines want to operate at. In order to raise the boiling point of the water, we pressurise the cooling system.
• If we allow the water to freeze, it will crystallise and turn to solid ice. When it does this, it will expand and crack the system in which it is contained. In the case of the cooling system, this means the engine block and hoses can get damaged.
  To avoid this, we add anti-freeze to the water.
• Water causes corrosion, so we must add some sort of inhibitors such as rust inhibitors.
• Water causes scale - just look at the element in an old electric kettle. To avoid scale build up inside the water passages of the engine, we add inhibitors. Scale build up will restrict proper coolant flow and slow down heat transfer.
• Whilst pure water is a poor conductor of electricity, the water found in cooling systems is not pure, and it will conduct electricity. A liquid that conducts electricity is known as an elecrolyte.
  In addition, inside a cooling system, there are many different types of metals.
  This makes a liquid cooled engine one big battery: dissimilar metals immersed in an electrolyte. Because of this, coolant must contain some sort of electrolytic inhibitor.

Checking Coolant

All modern cooling systems are sealed and as a result they shouldn’t ever really need topping up between car services provided everything in your vehicle’s engine is functioning correctly. It is a pressurised system and as such should only be checked or topped up when the vehicle's engine is cold.

Benefits of coolant:

• No corrosion - By replacing corrosive water with engine coolant solution, you will prevent corrosion damage.
• No scale - Complete elimination of scale build up inside the water passages of the engine. In addition, "hard" fresh-water causes scale form, and this will restrict proper coolant flow and heat transfer.
• No electrolysis in the engine.
• Anti-freeze protection.

The Earth Leakage Circuit Breaker is a safety device used in electrical installations with high earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected.

Basically what it does is if the ELCB detects a voltage leak,it will open the circuit, stopping the machine from operating.

You can read more about ELCBs on Wikipedia

> means greater than -example 2 > 1

< means less than - example 1 < 2

≤ means less than or equal to.

≥ means greater than or equal to.

Lambda, a letter from the Greek alpahbet. In automotive engineering, it is used to represent the stoichiometric ratio of the amount of air required to burn a fuel. For example, for diesel, the value is approximately 14.5:1, meaning that it takes 14.5 parts of air to burn 1 part of diesel.

The stoichiometric ratio for petrol is approximately 14.7:1.

This is a Perkins designation, and refers to the 1100 series engine. The '4' refers to a four cylinder engine, and the 'D' refers to the common rail engine.

This engine has full electronic control of the fuel system - common rail with electronic injectors. 

As of April, 2012, we operate 3 of these engines.

This designation refers to the 1100 series Perkins engine. The '6' refers to the number of cylinders, and the 'C' refers to the fuel injection system, which is mechanical, based around a rotary fuel injection pump. This engine is the forerunner of the 1100D common-rail engine. Currently, the section is equipped with 6 1106C engines and 3 1104D engines.