2. Objectives:
• Understand a simple electric starting circuit
• Identify and explain the function of starting
system components
• Properly identify common starting system
malfunctions
12. Battery
• Supply energy to the coach when the engine
is not running
• Supply energy to the starter when the
engine is cranked
• Supply energy for coach’s electrical system
when the electrical demands exceed the
alternators output
22. Remember
YOU are our eyes and ears!
• The better your description is of what is
happening, the faster our mechanics can
properly diagnose the problem.
My goal is that in the next 10 minutes, you will be able to:
Now, since electricity is such an abstract concept because we can’t see electrons flowing thru a wire,,,,,Whats helped several people, including myself, is to compare electron flow with water flow,,, it’s a goodway to illustrate what’s going on here since there are so many similarities between the two. Water pressure from the tower is similar to the electrical pressure that the batterywould supply on a circuit,,, The water valve here represents our starter switch, which controls the starter,,,Now when I open the valve,,, The water begins flowing from the tank into the pipe,, which represents electron flowin wiring. The turbine represents the starter, which begins rotating,,, and cranking the engine over,,,, when the water leaves the turbine, it travels down a path towards ground.Now unless something breaks or our water source is depleted, this will continue to run as long as the valve is open,,, supplying a path for the water to the turbine,
Now here’s our basic starter circuit. Heres our battery, just like our water tower, which provides the electrical pressure to operate our circuitThe wiring provides a path for the electricity to flow, just like our water tower plumbingA starter switch, controls the starter, just like our water valveAnd finally, the starter which mechanically cranks the engine.
Now from the electron’s point of view, there are only 2 types of materials we are concerned with today,,, Conductors,,, which have what’s called a “free electron” which orbits the atom with a weak attraction to the nucleus. This is what makes ALL electrical devices work,,, without these free electrons, there would be no conduction or flow of electrons, and no electricity! The opposite is true about all insulators,,, these atoms have several electrons in their outer shell with a strong bond to the nucleus. These atoms do not give up their electrons easily, and therefore,,, do not shed free electrons necessary for current flow.Examples of Conductors are:Copper, iron, silver, aluminumAnd examples of Insulators are: Rubber, wood, porcelain, polymers, plastic
Now knowing what we just learned, what can we say about this molecule? Based on it’s 1 “free electron” what type of molecule would this be? A conductor or an insulator?We at least know this atom is a conductor because of it’s one free election. For you chemistry junkies, this is #29 on your periodic table, otherwise known as copper
Since the relative cost of copper is low, and it IS one of the best conductors of electricity,,, it’s no real surprise that the majority of wiring on all of our buses is copper.
Now, just like our water pipe, electrons flow thru the copper wiring because of the “free electrons” availableCurrent flow is the movement of electrons from one atom to the next, and is ALWAYS from a negative source to a positive source
Something else to know is the speed of electron travel the wiring is a constant 186,000 miles / second, however the number of electrons moving at this speed can vary greatly depending cable size & construction. So just remember, the larger the wire, the greater amount of electron flow is capable of traveling thru it at any given time.
Now our ability to store electrical power started way back in the 1800’s when, one gentlemen by the name of Volta discovered that when you place 2 dissimilar metals in electrolyte, that an electromotive force is produced between the two metals. People were so astounded with his discovery, they decided to name the electromotive force that Volta discovered after him,,,,,,, aka,,,the volt.
This shows us the chemical reaction that occurs inside the battery. All you need to know is when the battery is discharging, the electrolyte reacts with the lead plates positively charging one plate, and negatively charging the other. This is what creates the electromotive force for electron flow to occur.When the battery is completely discharged, all the electrolyte has reacted with the lead plates,,,, it then provides no electromotive force,,,, and all that’s left in the battery is water.
Now since we can only produce approximately 2 volts per cell,,, we need to stack these cells in series to create the voltage necessary for proper operation.
Completes the circuit, and allows current to flow to the control side of the starter, energizing the solenoid
On the schematic, the “S” terminal of the starter is connected to is the starter switch. As the starter switch is closed, it allows current to flow into the starter solenoid, causing it to operate. And were going to see shortly how this works.
This is one of the starters that we utilize in our bus fleet. This is a DelcoRemy 50 MT starter that’s found on all 1900 and 2800 intercities equipped with series 60 detroit diesels.Now by definition, A starter is an electric motor which rotates an engines crankshaft so as to initiate the engine's internal-combustion cycle under its own power
Here’s the spec’s for this type of starter. The one spec that you need to be aware of is the last one. It is possible with this starter to crank an engine over constantly,, which can overheat the starter and other starting system components real quick. It should take no longer than 5 seconds of crank to start an engine. If it does, then that’s because something is wrong.
Heres a cutaway of the starter, essentially all it is,,,,is a large electric motor, and a solenoid. The solenoid is what’s called an “electromagnet”. This is basically a magnet that can be turned on with current flow.
When energized, the solenoid has 2 jobs, one to engage the pinion gear with the teeth on the flywheel, and two, to allow power to the starter motor.
Now, lets look at some starting problems that we see.Actually, this is NOT a problem with the starting system. The only job the starter has is to crank the engine over fast enough to start combustion. This is going to be a problem with the engine, no fuel, no power to the ECM, ect. If the engine does crank, but does not start, DO NOT continue to crank it in hopes that the engine will eventually start. Again, remember, these starters DO NOT have an overcrank protection!!! With the amount of current that goes thru these starters during cranking, it doesn’t take long to turn that 80 lbs starter into a glob of melted metal. It shouldn’t take no longer than 5 seconds of crank time to start any of our buses,,, and if it doesn’t start, release the starter, and let it cool before trying again, while your waiting, write down the problem in the book,
Now clearly, this is a malfunction of the starting system. Sometimes you wont even get a click, or maybe a rapid clicking. Typically on these scenarios, the batteries are discharged to the point where there’s not enough current to crank the engine over, you may also notice the lights in the coach may also be dim or flickering. Sometimes the starter or the circuit will have high resistance that causes this, or possibly a burned out section of the armature, or worn brushes, That’s where you’ll see someone in the engine compartment striking the starter with a hammer and prybar trying to jossle the components around trying to get it to turn over.It can also be an engine mechanical problem, but is rare.
Just remember YOU are our eyes and ears! Sometimes these problems are intermittent, and can be difficult to duplicate for diagnosis,,,, So The better your description is of what is happening, the faster our mechanics can properly diagnose the problem.
