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CH15 basics of electrical systems STUDENT VERSION rev

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Tài liệu học tập cơ bản khái quát về động cơ và các bộ phận trên ô tô phiên bản tiếng anh. Tài liệu này nhằm giúp chúng ta tiếp cận được cấu tạo chức năng của các bộ phận của xe. Với tài liệu này giúp các bạn sinh viên ngành cơ khí ô tô tiếp cận được những kiến thức cơ bản về ô tô và đồng thời nâng cao kiến thức tiếng anh. Bộ tài liệu này được soạn thảo bởi trường đào tạo và huấn luyện nghề ở Canada.

Chapter 15 Basics of Electrical Systems Basics of Electricity • Provides power for lights, TVs, stereos, and other household items • Basis for communication between our brain and the rest of our body • Cannot be seen, the effects can be seen, felt, heard, and smelled Flow of Electricity • Electricity is the flow of electrons from one atom to another • Energy is released as electrons move Flow of Electricity (cont’d) • An electrical power source provides a more positive charge • Supplies free electrons to maintain the continuous flow of electricity Flow of Electricity (cont’d) • To have continuous flow of electricity: – Must be an excess of electrons in one place – Must be a lack of electrons in another place – Must be a path between the two places Flow of Electricity (cont’d) Automobiles use two power sources • Battery – Uses chemical energy to provide energy – Produces direct current electricity • AC Generator – Moves magnetic field passed a conductor – Produces alternating current Amperage or Current • DC current – flows in one direction only • AC current – electrons change direction at a fixed rate • Automobiles typically use DC • Some components generate or use AC Voltage • Electrical pressure • The force developed by the attraction of the electrons and protons • The more positive one side of a circuit is, the more voltage is present • Voltage does not flow • Also called electromotive force (EMF) Voltage Resistance • • • • • When any substance flows, it meets resistance Resistance to electron flow can be measured Resistance produces heat Loads are good resistance Too low or too high resistance can cause circuit faults Types of Circuit Protection (cont’d) • Circuit Breaker – Is designed to open when circuit current exceeds a given point – Most will reset when current flow stops • PTC Circuit Protector – Its resistance increases when current rises above a specific level Switches • Can be normally open (NO) or normally closed (NC) • Simplest form is a single pole, single throw (SPST) • Some have one input and two outputs (SPDT) • Can have several inputs and/or several outputs (ganged switch) Relay Characteristics • Relay – Uses a small current circuit to control a larger current circuit – Uses an electromagnetic switch to open or close contacts that control the larger current – Can be normally open or normally closed Typical Relay Conductors and Insulators • • • • • • Conductors have low resistance to current flow Four or fewer electrons in outer shell or ring Most metals are conductors Insulators resist current flow More than four electrons in outer shell or ring Thermal plastics most common Conductors and Insulators (cont’d) • Conductor resistance depends on: – Length of wire – Diameter of wire – Temperature of wire • Double wire length – double the resistance • Double wire diameter – halve the resistance • Increase wire temperature – increase resistance Wires • Solid Wires – Single strand conductors • Stranded Wires – Most common • Size standards established by SAE, called American Wire Gauge (AWG) • – 40, is largest and 40 is smallest Closed Circuit Open Circuit ... the continuous flow of electricity Flow of Electricity (cont’d) • To have continuous flow of electricity: – Must be an excess of electrons in one place – Must be a lack of electrons in another... heard, and smelled Flow of Electricity • Electricity is the flow of electrons from one atom to another • Energy is released as electrons move Flow of Electricity (cont’d) • An electrical power source... value of the series resistor Characteristics of a Series-Parallel Circuit (cont’d) • The total amperage is the sum of the current flow through each parallel branch • The total amperage of each

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