On gasoline engines the primary method for causing the fuel air mixture to become ignited is to use a spark. The spark is generated using high-voltage electricity which jumps across a gap in the engine combustion chamber. We all understand this process that the spark plug must give spark and therefore the engine will run properly, however we don’t generally understand how the spark is generated and what the mechanism is that causes this whole event to occur.
In this particular discussion we will talk about magnetos and solid state ignition systems, additionally we will talk about old-fashioned car coil systems because often times larger two cylinder engines will use a coil which operates off the battery.
Understanding ignition systems is that you are trying to manage high-voltage electricity. As we all well know when you put your hand on a high-voltage fence (such as an electric fence to hold cows in the pasture) is a very large hair-raising experience which is very unpleasant.
Trouble is when you’re trying to manage or regulate high-voltage electricity it can do some damaging effects to electronics and circuitry. So the better method is to use secondary systems that don’t need or have wear components to them that would be affected by the high-voltage electricity.
The best way to manage the high-voltage electricity is though magnetic fields because magnetic fields don’t have mechanical parts to them. They are, if you will, unseen forces that can hold caustic and dangerous environments at bay.
For example magnetic fields are used to constrain high temperature plasma gas such as is used in a fusion reactor. Man-made magnetic fields are used to contain the fusion gas and therefore protect the mechanical containers from becoming destroyed.
The same concept is being employed when managing high-voltage electricity but out of smaller, more cost-effective and downsized package. The magnetic field is being used to work with high-voltage spark plug of electricity.
To analyze the ignition system for a small engine we are going to start with the earliest design which was the magneto points system.
The magneto points system consists of a flywheel with the magnet in it, a magneto, and a points system.
Basic magnetic theory is that when a magnetic field passes by an electrical wire it induces an electric
current in the wire. This basic concept is used to generate electricity in power plants. A magnet is passed by electric wires and electric current comes out of these wires and is used to light bulbs in your homes. That is the down and dirty simple explanation of how electricity generated.
The concept is that when a magnetic field is passed by a wire it generates electricity.
A similar concept is used in generating magnetic fields. When a coil of wire is wrapped around an iron core and electricity is introduced into the wire a magnetic field is generated.
Now you can do a combination of making a magnetic field using electricity and taking a magnetic field that was just generated and causing electricity to be generated by the magnetic field that was just generated.
That sounds like a perpetual motion machine. Actually it’s not a perpetual motion machine is more like a open tube. Water will flow fine through the tube, but when you restrict tube the flow out of the tube will
be less and the pressure may be higher.
What were are talking about is the concept of a transformer where electricity is generated on one side and stepped up or down on the other side of the transformer. The requirement however for the transformer to actually work is that the magnetic field is constantly being created and destroyed. The destruction meaning the collapsing of the magnetic field is where the electricity is generated.
The magnetic field in other words is falling back from where it started from and during this falling back phase it falls through wires and can generate electricity. The generating of electricity is based Faradays’s law of magnetic fields.
So a magneto is a glorified transformer that is turned on and off at certain times so that high-voltage electricity can be shoved through the spark plug. The turning on and off of the transformer is accomplished by the points.
The magnetic field for the first wire, which is called the secondary wire in a magneto is generated when the magnet on the flywheel passes by it. The points suddenly opened causing the magnetic field to collapse because the circuit is shut off. The collapsing magnetic field passes through the windings inside the primary coil winding causing a large spike in the electrical voltage. This sudden spike in electrical voltage is called a spark as we see in a spark plug.
There certain parts of the magneto system that are designed to absorb electricity so that they are not worn out during the whole process of switching. The device that were talking about is called a capacitor. The capacitor takes the electricity that would like to jump across the points gap and absorbs it or cushions it in the condenser or capacitor.
A capacitor is kind of like a spring. It absorbs the energy of the electricity and prevents it from actually jumping across the point gap. The reason for this is that the points will become pitted and soon become dysfunctional or non-operational if the condenser or capacitor is not in the circuit or working properly.
On a car a coil is used to act as a high-voltage switching device. Up till about the late 80s and early 90s coils were used extensively to supply high-voltage current to distributor caps even though points were not being used in the system. The switching was accomplished using solid-state circuitry, however that basic concept of switching a coil “on” and “off” was still maintained.
What occurs with the coil is that the coil is activated and deactivated using a switching device. The coil consists of two sets of coil wires. One set of coil wires is wrapped first on the iron core. The second coil of wire is wrapped around the first coil wire system.
The first wire has 12 V of electricity that is induced into the circuit. When the electricity is turned off to the coil a magnetic field correspondingly collapses back into the first coil wire system. This collapsing magnetic field passes through the second set of windings causing a large high-voltage electrical current to pass through it. This high-voltage electrical current is used to cause a spark in the spark plug.
The means to cause the coil to turn on or off a points system or a solid-state circuitry device is used.
Solid-State Magneto System
The solid-state magneto system uses electronics to do the switching. Typically the electronics uses a magnetic field again, to activate a Hall effect sensor which does the switching.
So when a magnetic field passes by from the magnet on the flywheel and Hall effect sensor
(a switch that is activated by magnetic fields) collapses the secondary field, or causes the circuit to be opened up and stop functioning. Remember when the secondary circuit is open up, the magnetic field collapses because electricity is being pushed through it anymore the electricity must return from where it came or collapse the magnetic field.
On a car the same principle is used to generate high voltage sparks. The solid-state switching is accomplished using computers and Hall effect sensors mounted on the engine block close to the main belt drive system.
The nice thing about solid-state systems is that their compact and they don’t require mechanical linkages such as fly wheel weights, vacuum lines and other complications.
Troubleshooting Ignition Systems
The question comes in when you’re troubleshooting these electronic systems how do you know what the problems are?
Well the troubles occur in the following three areas regardless of whether or not it is a solid-state ignition system or not:
1. Ignition coil
3. Main power
The ignition coil is the device that switches magnetically to high-voltage using an on off the circuit. The switching device is what turns on and off the coil. The coil must first be excited or full of electricity before it can be collapsed. So an electrical current is required to be generated first in to the coil.
In a small engine the electricity is generated using the magnet of the flywheel. The magnet obviously must exist on the flywheel. If there is no magnet there is no electricity being generated.
The first thing to examine is whether or not there’s a magnet in the flywheel. In other words is a magnet dead or not? To test this put a screwdriver or a piece of metal on the flywheel magnet and if it holds it in place then the magnet is fully charged.
The second thing to examine is whether or not the points system is working properly or not. This requires inspection of the points system. If the points are painted they need to be scraped and cleaned. This will keep at bay the problem of nonfunctioning ignition system, however it is indicative of a points system that needs to be replaced and most especially a capacitor that is faulty.
On a small engine that does not have points if you’re not getting spark when the magnetic field passes by from the flywheel then the solid-state ignition is faulty. There is one exception to that rule however and that is the way he a solid-state ignition system is turned off. The solid state ignition is turned off when the wire coming out of the solid-state ignition system is grounded. What this does is when you take the circuit, (even though it is internally solid-state )and ground it to the framework of the engine the circuitry fails to function properly and the magnetic field is not collapsing anymore therefore no more spark is being generated.
So if the grounding wire is off of the framework, or is not shorting onto the frame of the engine, then the solid-state ignition system should be working properly and you should get spark. If at this point in time you are not getting spark than the solid-state ignition system is faulty.
(Note: a way to destroy a solid-state ignition system is to induce electric fields into the grounding wire. The solid-state ignition system is not designed to take high-voltage electricity or any electricity for that matter and back-feed it into the grounding wire. A common problem that occurs with solid-state ignition systems is that the alternator wire is accidentally hooked on to the grounding wire. What this does is that it induces an electrical current into the solid-state module and burns out the Hall effect sensor circuitry. So beware of putting any sort of current onto the solid-state wire system.)
Coil System Trouble Shooting
On a larger engine that uses a coil system the general principles basically simple. An electrical current is being generated by inducing a voltage through the secondary circuit. When this secondary circuit is turned off the magnetic field collapses through the primary wire and causes a high-voltage to come off the center of the coil. So if the system is not working it typically is not the coil’s fault, it typically is the switching device that is at fault.
Care must be taken to make sure that the solid-state ignition system which is turning the coil on off has the correct wire coming off of it. All that is required for this system is electricity is turned on to the solid-state ignition module and electricity then flows from the module to the coil. The module acts as a switch turning on off. The way the module turns on and off users typically a magnetic field off of the engine flywheel.
From a packaging standpoint the coil switch is a simple device bolted near the flywheel magnet interface.
Bottom line is that an ignition system is trying to manage high-voltage by switching using low-voltage. The complication comes when you’re trying to turn on and off the low-voltage circuitry. This can be accomplished using a mechanism such as points, or a Hall effect sensor such as a magneto uses, or a computer as is used in a car.