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HVAC System Controls Electrical fundamentals What is electricity? How is it measured? Uses Complete circuits Malfunctioning circuits Ohm’s Law Series and parallel circuits Testing equipment 1 Electrical Fundamentals What is electricity? How is it measured? What does electricity do on AC Units? 2 What is electricity? Electricity is defined as the flow of electrons 3 What is electricity How can we get electrons to flow? 1. Source 2. Path 4 What is electricity? Source: something that has an imbalance of electrons and protons Protons are positively charged Electrons are negatively charged Since opposites attract, if we create an imbalance of electrons and protons we have electrical potential Electrical potential is electrical pressure and it is measured in volts 5 What is electricity? 6 Path: a conductor that connects the protons with the electrons A conductor is anything that has less than 4 electrons held loosely in their atom’s outer orbit This allows the electrons to move freely from one atom to another An insulator holds its electrons in a tighter orbit and does not allow movement easily Once a path is established, electrons will move because of the attraction caused by the imbalance in the source What is electricity? How do we know electrons are moving? Can we hear, see or feel electrons moving? We can only see the effects of electrons moving Electrons if left unrestricted, will move so fast that extreme heat is created from the friction generated by their movement 7 What is electricity? For safe movement, electrons must be restricted in their movement We can use the restrictors to do work for us on an automobile 8 What is electricity? Electricity: flow of electrons What is required for electrons to flow? A basic circuit What is a basic circuit? Source Path Restriction or load 9 How is it measured? 10 Volts: electrical pressure or potential Volts do not move through circuits Voltage is simply the strength of the imbalance between protons and electrons and force the electrons to move through a conductor Voltage is measured with a voltmeter that measures the imbalance between the positive side and negative side of a circuit Voltmeters must be wired in parallel How is it measured? Amperes: the measurement of the amount of electrons flowing through the circuit Amps are the measurement of current in an electrical circuit Amps are measured with an ammeter For an ammeter to measure current in a circuit, the current in the circuit must flow through the ammeter Ammeters must be hooked up to a circuit in series 11 How is it measured? Ohms: a measurement of electrons resistance to flow through a circuit Resistance must be present in a circuit to control the flow of electrons Resistance in a circuit can be measured with an ohmmeter An ohmmeter is self-powered and requires the circuit to be open 12 How is it measured? What unit of electricity is doing work? 13 Sources: 14 Electrochemistry: different metals placed in a chemical solution causes a difference in electrical potential or voltage between the two types of metal Electromagnetism: when a conductor is moved through a magnetic field, an electrical current is produced Sources: 15 Piezoelectricity: when pressure is applied to certain types of crystals, they develop a potential difference or voltage Photoelectricity: certain types of metal can produce a flow of electrons from light exposure Uses for electricity on the automobile: Heat: windshield/seat heaters, etc. Electrical resistance creates heat Illumination Magnetic fields: rotary and linear motion; electricity generation; voltage transformers Chemical reactions Electronics: Logic; computers- modules; sensors; etc. 16 Complete circuit: Power source Protection Insulated path Load or resistance Return path 17 Malfunctioning circuits: Open circuit: lacks continuity or is incomplete 18 No current will flow Shorted circuit: a portion of circuit is “short-cut” Short to voltage Short to ground Current may or may not flow May or may not blow circuit protection Circuit control can be lost High resistance Causes a decrease in current Open circuits Causes: 19 Shorted Circuits Short to voltage: 20 Short to ground: Shorts to ground may not necessary blow fuse Ohm’s law: 21 Establishes that pressure, resistance and amount of current flowing through any circuit are all related If two values are known, the third value can be calculated It takes 1 volt to push 1 amp through 1 ohm of resistance Ohm’s law: 22 Series circuits A circuit that has more than one load and all current flows through all the loads in the circuit Series circuits used in an automobile: Blower circuit where variable fan speeds are required Seat heaters using a variable resistor to control temperature 23 24 Example of a series circuit for a blower motor Series circuits Total of all voltage drops will equal the source voltage voltage drop Voltage drop is proportional to resistance The higher the resistance, the greater the voltage drop As resistance increases, current flow decreases Circuit resistance is the sum of all loads in the circuit Amperage is the same at any point in a series circuit voltage drop AC Delco 25 Parallel circuits A complete circuit with more than one path for current to flow Current flowing into each branch or leg varies according to the amount of resistance in that branch of the circuit The total resistance of a parallel circuit is always less than that of the smallest resistance of any branch of the entire circuit The voltage is the same for each branch of the parallel circuit 26 Parallel circuits Most of the current flow in a parallel circuit will occur in the branch with the least resistance As long as other branches of the circuit are complete, current will flow through them in accordance with Ohm’s law The only place where electricity can take the path of least resistance is in a series circuit Most lighting circuits on automobiles are parallel circuits 27 Series-parallel circuits Includes both parallel loads and loads that are electrically connected in series Added resistance in series portion of circuit, will decrease current flow through parallel branches evenly Example of series-parallel circuit used in automotive applications: dash board illumination with a dimmer switch As resistance increases with variable resistor in dimmer switch: current flow is decreased through dash lights 28 Testing Equipment Always test your test equipment before attempting to diagnose electrical problems Standard test lights have limited use on late model vehicles Test lights can draw enough current to Damage electronic components Deploy air bags Test lights cannot differentiate positive and negative sides of a circuit Test lights cannot measure resistance 29 Test lights Self powered test lights: battery operated and light up when connected to both sides of a circuit LED test lights should be used in place of standard test lights on computer controlled vehicles LED’s draw very small amounts of current and cannot damage electronic components 30 Digital multimeters 31 High impedance: high internal resistance that limits current output Can measure amps, volts and resistance Automotive requirements for a DMM: Diode checking Frequency Temperature Duty cycle RPM Dwell DMM’s/DVOM’s 32 Voltmeter: measures difference in voltage between leads Must be hooked up in parallel Internal resistance keeps meter from affecting circuit being tested Ammeter: measures amount of current flowing through circuit Most Must meters cannot measure more than 10 amps be hooked up in series or installed inside of the circuit to measure amount of current flowing DMM’s/DVOM’s Ohmmeters: Requires open circuit Ohmmeter is self powered and may be damaged if connected to a live circuit Zero ohms means no resistance in circuit or continuity Meter use: Select proper unit for what is being measured Place leads in proper input sockets Make measurement Interpret reading 33 34 FLUKE 87 AC Switches DVOM’s Use of DVOM’s: Select proper unit for what is being measured Place leads in proper input sockets Make measurement Interpret reading 35 DVOM’s “OL”: Displayed on most meters What it means: Open leads Infinite resistance Over limit Over maximum meter can read 36