Agriculture Engineering-chptr 8


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Agriculture Engineering-chptr 8

  2. 2. Operation of Starting Circuit• The starting circuit converts electrical energy from the battery into mechanical energy for starting the engine
  3. 3. Basic starting circuit has 4 parts:a) Battery - supply energy to the circuitb) Starter switch - activate the circuitc) Motor switch - engages the motor drive with the engine flywheeld) Starting motor – Drives the flywheel to start the engine. As soon as the engine starts, the starting motor disengages. It is designed to handle heavy loads for short periods of time only
  4. 4. Battery chargingThe amount of electrical current a battery can produced islimited by the amount of chemical reaction which can takeplace within it.When chemical reaction in a battery has ended – battery isdischarged and can no longer produce a flow of electricalcurrentDuring discharged current flow from +ve terminal to –veterminalThe battery can be recharged by causing direct current fromoutside source to flow from –ve to +ve terminals
  5. 5. Coil IgnitionIgnition Circuit (spark ignition engines)The ignition circuit creates the spark which ignites fuel-air mixture to power petrol engines. To do this, it must : a. Step up low voltage to high voltage surges b. Time these surges to the engine cycle
  6. 6. Ignition circuit has these parts:a. Ignition coilb. Condenserc. Distributord. Spark plugse. Ignition switch
  7. 7. a) Ignition Coil The coil transforms low voltage from the battery to the high voltage for producing a spark.Operation of Ignition Coil The ignition circuit must take low voltage from the battery and create high voltage to fire spark plugs It must do this very accurately and very rapidly 100 or more times per second This is why maintenance is so important
  8. 8. i) Primary Circuit• Path for low voltage current from source (diagram)• It includes these parts: – Ignition switch – Coil primary winding – Distributor contact points – Condenser
  9. 9. ii) Secondary Circuit High voltage path for current stepped up by the coil It includes these parts: Coil secondary winding Distributor rotor Distributor cap Spark plug wires Spark plug
  10. 10. Operation of the CircuitDivided into 2 parts1) Before distributor points open – Before engine start, distributor points closed – When ignition is turned on, current flows from battery into primary windings of the coil – This current creates a magnetic field around the winding – From primary winding, current at low voltage travels through the closed distributor points and back to ground – This is why the battery can be completely discharged if the switch is left on when the engine is not running
  11. 11. 2) After distributor points open – As the engine rotates in starting, it drives the distributor shaft and the breaker arm – When the breaker cam opens the distributor points, the second phase of ignition begins – As the points open, they open the primary circuit and divert the flow of current to condenser, which stops flow in the primary circuit – Stopping this flow causes the magnetic field around the primary winding to collapse very quickly – This collapse induces a voltage in the primary winding which causes current to flow. The current in the primary circuit is absorbed by the condenser
  12. 12. • The collapsing field further collapses across the secondary winding and induce voltage in it also• The secondary has more turns compares to the primary winding (stronger winding). Therefore higher voltage is induced – 4,000 to 20,000 volts• High voltage pushes current through second winding and high tension terminal into the distributor cap (Diagram)• The rotor inside the distributor cap turns to a spark plug terminal, directing the voltage surge to correct spark plug through insulated cables• At the spark plug, current flows down the center electrode, jumps the gap, and creates the spark• The whole cycle happens from 50 – 150 second depending on the speed of the engine
  13. 13. Maintenance of Electrical Systemi) Servicing and maintenance of batteryii) Servicing of spark plugsiii)Servicing the distributoriv) Replacing breaker pointv) Servicing alternator and starting motor
  14. 14. THANK YOU