Module 12- Section 2- narrated

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Information about Module 12- Section 2- narrated

Published on March 1, 2014

Author: pmgreenwald1


Module 12- Section 2: Module 12- Section 2 Basic Electricity and Power Supplies Backup Power Devices 1 I. Basic Electric Quantities: I. Basic Electric Quantities The four basic electric quantities are: Voltage Current Resistance Power 2 PowerPoint Presentation: A. Voltage - is a "potential difference.”       this “potential difference" exists between two points electrically       Has the "potential" to cause electrons to move 3 PowerPoint Presentation: Voltage is also referred to as electrical pressure since a difference in voltage between two points is necessary for electricity to flow just as a difference in pressure between two points is necessary for water to flow. 4 PowerPoint Presentation: Batteries have “voltage”- Example: a 9-V or a 6-V battery. The type of voltage supplied by a battery is DC voltage- DC stands for direct current. 5 PowerPoint Presentation: DC voltage is constant with time (does not vary). The term DC is applied to both voltage and current. Power supplies provide DC voltage. 6 PowerPoint Presentation: The voltage available at a wall outlet is AC voltage. AC stands for alternating current. AC voltage is cyclical and the waveform is a sine wave. 7 PowerPoint Presentation: 8 PowerPoint Presentation: Typical household voltage is 120 Vac alternating at 60 cycles/second (Hz) in the United States. Line voltage can be as low as 110 V. The AC cycle repeats every 16.7 ms. 9 PowerPoint Presentation: In Europe, line voltage is 220-240 V alternating at 50 Hz. At 50 Hz, line voltage repeats every 20 ms. 10 Basic Circuit Principle:: Basic Circuit Principle: Electrons are the basic moving parts in an electric circuit, they are abundant in conductors (such as metals). For the electrons to move, they must be given a complete path between two points of different electric potential. 11 PowerPoint Presentation: A simple electric circuit would connect a battery to a light bulb. A complete path form the + terminal of the battery to the – terminal through the light bulb is required. 12 PowerPoint Presentation: Voltage can be provided by a battery or a power supply The moving electrons are what cause “current.” 13 PowerPoint Presentation: B. Current: Current is measure of how many electrons flow in a given period of time. Current is measured in amperes (usually abbreviated amps) Current can be referred to as “amperage.” 14 PowerPoint Presentation: Once the circuit containing the battery and bulb is complete, current flows through the bulb causing it to light. We would say that the bulb draws current. 15 PowerPoint Presentation: The amount of current that the bulb draws depends on the third basic electric quantity- resistance. 16 Another Basic Electric Quantity: Another Basic Electric Quantity C. Resistance: the opposition to the flow of current. Conductor have low resistance, insulators have high resistance. Resistance is measured in ohms ( W) 17 PowerPoint Presentation: A light bulb’s filament offers resistance to the flow of current. The relationship between the current, voltage, and resistance is known as Ohm’s Law. 18 PowerPoint Presentation: In a circuit, wires offer little resistance. If the bulb were not present in the circuit, the wires would draw a lot of current and quickly drain the battery. 19 PowerPoint Presentation: When circuit elements “short out” their resistance becomes very small which causes the amount of current that flows to become very large. Large currents can overheat wires, melt insulation, and thus cause fires. 20 PowerPoint Presentation: The general relationship is: Small resistance- Large current Large resistance- smaller current 21 PowerPoint Presentation: Resistance is related to continuity. Flow through devices such as fuses and cables have low resistance. This is referred to as continuity since it is easy for the electrons to flow through. 22 Basic Circuit Quantities (cont): Basic Circuit Quantities (cont) D. Power The rate at which energy is delivered to a circuit or device Measured in Watts, sometimes called wattage 23 PowerPoint Presentation: The energy that is delivered to a device in a circuit is what makes things happen. In a light bulb, electrical energy is converted to radiant energy (light) and thermal energy (heat). 24 PowerPoint Presentation: Power is a measure of how much electrical energy is converted in a particular time period. A 100 W light bulb converts more energy in the same amount of time than a 60 W light bulb. 25 Electrical devices are rated in terms of how much power they use:: Electrical devices are rated in terms of how much power they use: Examples of Power ratings 1200 W (Hair dyers and microwave oven) 600 W (small microwave oven) 60 W (light bulb) 26 PowerPoint Presentation: PC power supplies are rated in terms of the maximum amount of power that they can deliver . Typical computer power supplies are rated as 350 W, 400 W, 500 W, 750 W etc. 27 Power Consumption in the PC:: Power Consumption in the PC: These things contribute the most to power consumption in the computer: Fans CPU speed (faster CPU- more power) Graphics card complexity (and fans) Hard drive, CD/DVD motors Memory circuitry 28 Typical Power Usage for a PC:: Typical Power Usage for a PC: during boot, power consumed in watts is close to 110 W during idle , no power management, close to 60 W during full power saving , no hard disk spin, machine in sleep mode, 35 W 29 PowerPoint Presentation: It is difficult to come up with an average power consumption for a PC when in use because it varies so widely. Factors to consider- How many fans CPU speed Are drives (such as CD or DVD) in use Graphics card 30 Paying for Power: $$$$$: Paying for Power: $$$$$ We pay for energy consumption in the unit of kilowatt-hours. The kilowatt is a unit power ( 1 kilowatt= 1000 W) and the hour is unit of time- so how much power we use in a particular time period. 31 PowerPoint Presentation: As an example, suppose that a particular PC uses 200 W of power and that it runs for 4 hours each day. 200 W is (200/1000) 0.20 kilowatts 32 PowerPoint Presentation: The number of kilowatt-hours that is billed is 0.80 kilowatt-hours 0.20 kilowatts x 4 hour = 0.80 kW- hours 33 PowerPoint Presentation: If electricity is billed at $0.15 per kilo-watt hour, it costs this much to run the PC for 4 hours: (0.80 x 0.15) = 0.12which is 12 cents. In a week, that is 84 cents and in a month (30 day) that is $3.60. 34 PowerPoint Presentation: These costs add up over time AND increase substantially when there are many PCs running! Approximately 10 – 30 % of an IT budget can be used for electricity. 35 II. How to Select a Power Supply: 36 II. How to Select a Power Supply Considerations for Replacement: Match form factor to case- form factor refers to its physical dimensions In matching the form factor, you ensure that the power supply will fit in the case- AND that the outlets and switches match the openings for them. PowerPoint Presentation: Make sure it provides necessary connectors Match wattage capacity to system requirements Consider warranty, price, and additional features 37 Specifying a Power Supply: Specifying a Power Supply In addition to matching the supply to the case and ensuring it has the correct connectors: determine the maximum possible power consumption and then specify a power supply that provides more than that requirement. 38 PowerPoint Presentation: To Determine Power Rating: Consider all components inside case Consider USB and FireWire devices Get power from ports connected motherboard Web sites have wattage calculators 39 PowerPoint Presentation: 40 Table 4-5 To calculate power supply rating, add up total wattage PowerPoint Presentation: 41 Table 4-3 Measures of electricity PowerPoint Presentation: NOTE: The acronym PSU stands for Power Supply Unit. This is how the A+ certification exam refers to the power supply. 42 III. Reliable Power: III. Reliable Power A. Adverse Power Conditions Overvoltage: voltage greater than 130 V Spike: short duration overvoltage (typically caused by lightning) Surge: longer duration overvoltage (typically caused when power is turned on after an outage or when motors turn on) 43 A. Adverse Cond. (cont): A. Adverse Cond. (cont) Undervoltage: voltage at receptacle falls below 110 V Commonly known as a brownout Typically due to overloaded circuits Blackout: loss of power 44 B. Adverse Power Protection: B. Adverse Power Protection There are three devices commonly used to protect against adverse power conditions: Surge Protector Line Conditioners Uninterruptible Power Supplies 45 C. Surge Protectors: C. Surge Protectors Uses an electronic device (MOV) placed between the AC line and the receptacles to the PC to absorb overvoltage conditions While ALL electrical devices should conform to UL standards, a surge protector should conform to UL 1449. 46 C. Surge Protectors (cont): C. Surge Protectors (cont) Ratings: Clamping Voltage : minimum voltage level at which protection begins (lower is better) Transient Voltage Suppressing (TVS) rating: (also known clamping speed): maximum response time before protection begins (lower is better) Joule Dissipation Capacity : energy absorbed during overvoltage (higher is better) 47 D. Line Conditioners: D. Line Conditioners Also known as power conditioners Protect from overvoltage, undervoltage AND electrical noise Have ratings similar to surge protectors Follow UL 1283 standard for EMI/RFI suppression (EMI- electromagnetic interference; RFI- radio frequency interference) 48 Fig 4-25 Line Conditioner: Fig 4-25 Line Conditioner 49 E. Uninterruptible Power Supply: E. Uninterruptible Power Supply Provides backup power in the event of a blackout. Also provides surge protection and protection from brownout. Two Main Types: Standby Inline 50 E. UPS (cont): E. UPS (cont) Inline UPS: PC operates off of a continuously charging battery When ac power is lost, the battery backup continues for some short period of time Standby UPS: Only switches in when ac power is lost 51 E. UPS (cont): E. UPS (cont) “Intelligent” UPS: Allows monitoring of the UPS (for things such as battery status and quality of incoming ac voltage) from an icon within Control Panel Can be either standby or inline 52 Fig 4-30 : Fig 4-30 53 PowerPoint Presentation: 54 How UPS are Rated: How UPS are Rated A power supply is rated in Watts- in electrical terms this is called “real power” and is used to determine how much we pay for the electricity. 55 PowerPoint Presentation: For an AC load, the quantity known as “apparent power” takes into account reactive loads from capacitors and motors. Apparent Power is at best equal to real power but is typically greater than real power. 56 PowerPoint Presentation: Apparent power is rated in Volt-Amps (or VA). The computer, printer, and monitor are rated in terms of Watts but the UPS is rated in terms of VA. 57 PowerPoint Presentation: It is NOT safe to assume that Watts = Volt-Amps!! The VA rating of the UPS should be greater than the wattage rating of the PC power. 58 PowerPoint Presentation: For example: If the computer and monitor have a 400 W maximum combined load, the UPS should be rated at around 500 VA (about 25% higher). 59 PowerPoint Presentation: This is the end of the second section of Module 12. 60

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