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Induction • We have learned that electricity can create magnets. Called _____________? Electromagnets • Now we are going to talk about magnets creating electricity. • Keep them straight
Induction • Creating voltage with a magnetic field • Three things needed for induction • Magnetic field • Conductor • Relative movement Here we are moving a Conductor through a magnetic Field, inducing voltage into The conductor.
D.C. Voltage Voltage pushing the same way all the time pushes current only one way If we kept moving the conductor thru the magnetic Field the same way at an even speed, this is the kind Of voltage we would induce in the conductor
Induction Here we are moving the magnetic field past the conductor Inducing voltage into the conductor
1 Hertz (Hz) A.C. Voltage Voltage created first one way, then the other pushes current back and forth House A.C. voltage used in the United States Changes direction 60 times a second (60Hz) Frequency is measured in Hertz (Hz)
Induction review • Anytime a magnetic field is moving past a conductor, voltage is induced into the conductor • Can be increased by: • Larger magnetic • Larger conductor • Faster movement • Closer distance I’ve got it
Mutual Induction • Voltage induced from one winding into another • Only happens when magnetic field is building or collapsing
P V I Watt’s Law • Power (watts) is equal to Volts times Amps
Mutual Induction (stepped up) Remember your Briggs & Stratton Ignition Coil in Auto 1? Approximately 150 windings in Primary and 9000 in secondary Approximately a 1:60 ratio
Mutual Induction (stepped down) Typical step down transformer Same amount of energy - Reduced the voltage by 10 Increased the amperage by 10
Wire to my house Transformer stepping Down the voltage to 240 A.C. volts and Increasing the amps 13,800 volts pushing Current in through These two wires Compare the wire Sizes coming in and Going out Wires to all my six neighbors houses on the block
Common transformer Input = 120 VAC 5 W 42 mA Output = 12VDC 24W 200 mA
Self Induction • Voltage induced back into the winding that created the magnetic field when the field is shut off (collapsed) Usually 200 V to several thousand volts are self induced.Depends on the number of turns and the speed of collapse
Self Induction • 12 Volts won’t but this amount Can shock you!
Self Induction in a Relay • When current is shut off to winding to open relay, self induction will take place. • Voltage spike can easily damage a computerized controlled circuit • The high voltage will naturally be built opposite to the voltage that created it
Clamping Diode • Diode is a one-way electrical check valve • We will learn how they work later in the year • Allows current only to flow one way • The way the arrow points
What we have learned and used so far • Ohm’s Law, Watt’s Law • Circuits • Components, Series, parallel (ATECH 1-11) • Problem circuits • Open, high resistance, short, grounded, short to voltage, low voltage (ATECH 7 & 11) • Meters • How to read, use, how to find faults (ATECH 1-11) • Wiring schematics • How to read, draw, interpret symbols, and trace (ATECH 4-11) • How magnetism and electricity relate • Electromagnets, Relays, Induction
Ignition • Lets take what we know and apply it to one specific circuit in the automobile
Primary Ignition circuit • Used to make spark for Power Stroke • Changes the 12 volts in the battery into as much as 50,000 volts for the spark at the spark plugs • This is easier than our Briggs & Stratton engines last year. • We started with no voltage and created as much as 15,000 volts all by starting with a magnetic in the flywheel moving past an armature and coil assembly (Magneto Ignition System) • Used today on many race cars so they don’t have to carry the weight of a battery
Ballast resistor Coil Distributor Condenser Primary Ignition Schematic (point type) Fill it in on your handout Ignition switch Battery Points
Primary Ignition Parts • Battery • Supplies voltage to circuit to push current flow • Ignition Switch • Turns on and off circuit • Resistor • Uses up voltage and lowers current flow • Coil • Step up voltage
Primary Ignition Parts • Distributor contains: • Points • Switch on and off primary circuit for proper spark timing • Condenser • Absorbs electrons when points are opening
Ignition Coil Has two windings: Primary wrapped around The Secondary Both Windings wrapped around an iron core
Positive Terminal Labeled: “+” “Batt” Negative Terminal Labeled: “-” “Dist” Primary Winding Secondary Winding Connects from + to – inside coil Connects from – to center of coil Coil wrapped in metal shield, insulated inside with, glass, tar, epoxy, oil Ignition Coil Fill it in on your handout Has about 200 windings Standard resistance is 1.5 ohm (+- 1) Has about 25,000 windings Standard Resistance is 8,500 to 12,000 ohms Approximately 200V are created during self induction Can create approximately 30,000 volts (30 KV)
Saturation Shorted coil Two coil ramps Taken with a Lab Scope and An amp probe. Saturation point Turn on point About 4.25 mS Amps = magnetic field Saturation point Turn on point Time in miliseconds
Turn Key On 1.5 ohms Points Closed Primary Ignition Operation 12 V in Battery will push ______ amps through primary circuit 4 1.5 ohms In 3 to 5 mS, a large magnetic field is formed around primary winding
Turn Key On 25,000 Volts 1.5 ohms Primary Ignition Operation 12 V in Battery will push ______ amps through primary circuit 0 1.5 ohms The magnetic field will collapse rapidly and induce high voltage into secondary Points Opened
Demo Time Hey, I have got To see that in Real life. It can’t be that simple!
Primary Ignition Review • Key on, points closed • Current flows, magnetic field builds up • Points open • Current stops flowing as condenser absorbs electrons that want to jump gap • Magnetic field collapses moving rapidly past secondary windings • High voltage is induced into secondary windings • We have spark
What opens the points? • What we need is a mouse in the distributor to push open the points every time we need spark for every cylinder? What happens when I get tired?
What really opens the points? • Points are opened by a “cam” in the distributor • Distributor is driven by the Camshaft • Camshaft and distributor are at a 1:1 ratio • Distributor is at half speed of crankshaft
Dwell & 4 cyl. distributor cam • Maximum dwell (points always closed) is 90o • Dwell is the time in degrees the points are closed • Measured in degrees of distributor rotation • 4 cylinder distributor cam has four sides • Specs. Usually call for 35o to 55o 90o x 4 360o
Questions • If the distributor for a 4 cylinder makes one revolution, how many times will the points open? • What happens every time the points open after current has been flowing through them? • How far will the crankshaft have turned
6 cylinder distributor cam • Distributor cam has 6 sides (hex) • Maximum dwell is ________ degrees 60o • Specs. Usually call for 30o to 40o
8 cylinder distributor cam • Has 8 sides (octagon) • Maximum dwell is 45o • Specs. Usually call for 26o to 32o
8 cylinder distributor cam 30 degrees of dwell, 15 degrees of point opening
Why a minimum Dwell? • Points have to be closed long enough to reach magnetic field saturation in coil. • No problem at low speed but is at high speed. • For an 8 cylinder, 6000 RPM is about maximum RPM with point type ignition • Ready to try to earn 10 extra credit points? • To earn, you are going to have to apply what you have learned up to now.
Extra Credit • Tear out a piece of paper, put name on top • Must show ALL your work to get any credit. • No calculator • No talking or looking at anyone’s paper to get credit • You have 4 minutes starting now
How many times are the points opening per second at 6000 RPM on an 8 cylinder engine?
Answer WOW • Need to know to figure this out • Engine RPM is measured in Crankshaft speed • Distributor turns half crank speed • 6000 divided by 2 = 3000 distributor RPM • In one distributor revolution the points open eight times on an 8 cylinder • 3000 times 8 = 24,000 point openings per minute • There are 60 seconds in a minute • 24,000 divided by 60 = 400 Point openings per second at 6000 RPM
Point float • Must have good point spring tension or points will not close (float) when they are suppose to
Why a Maximum Dwell • What would happen if we set the dwell to 44o • Don’t forget to lubricate points when renewing
How to hook up Dwell Meter • Red lead to “-” side of coil • Black lead to ground • Select proper number of cylinders • Can read while cranking or running • Might change a few degrees between cranking and running