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Issue link: http://read.dmtmag.com/i/128655
By Dave Worden Electrical Troubleshooting – Where there is smoke F or years, technicians have often struggled with electrical systems and troubleshooting them. Today's electrical systems appear to be more sophisticated than electrical systems of say 10 years ago. The truth is electrical systems have not changed a great deal; manufacturers are just adding more features, which adds more things to look for when electrical systems start causing issues. My hope is to cover some basic guidelines and things to try and remember when looking at or troubleshooting an electrical or ignition system. In this article's headline, I mention "where there is smoke." What I mean by that is we have all seen both electrical and ignition systems work great until we see smoke. Electricity is said to be invisible; I say that is incorrect. When a system stops and smoke comes out, that is electricity! The key is to keep the smoke in the wires! No smoke — electrical system is working; see smoke — system stops! Ignition Systems In today's business, we are seeing solid state/CDI (capacitive discharge ignition) or simply electronic ignition systems. They are made up of transistors, diodes and sensors. If you are old enough to remember points, condensers, coils and laminations, then you have been working Figure 1 20 OUTDOOR POWER EQUIPMENT on systems as far back as 1967 (see Figure 1). One of the first solid state systems for lawn and garden engines was introduced in 1968! These older, for lack of a better term, solid state systems were mechanic pieces that had several serviceable parts: laminations, coils, breaker points, condensers, flywheels and spark plugs. A solid state or CDI system consists of the following: • Capacitor: The capacitor holds an electric charge or acts as a shock absorber to store the charge from the HV (high voltage) supply. During the second phase of the ignition cycle, the capacitor is discharged through the ignition circuit. • Switch: The switch transfers the energy stored in the capacitor to the primary windings of the ignition coil. This function is carried out by a SCR (silicon control rectifier). The switch is generally linked to a diode for the reverse current. • Sensor: The goal of the sensor is to synchronize the spark with the engine rotation. For the small motor, the sensor detects a bump at each engine revolution. For a multiple cylinder unit, the sensor system gives a pulse for each cylinder or ignition point. • Conditioning: The conditioning is a very important stage that must assume the following functions: – Optimization of the SCR gate current for all the rpm range. – Filtering of parasitic strikes occurring on the sensor signal. – For the most sophisticated small engine and multiple systems, it has to ensure the correct lead angle. • Ignition coil: The ignition coil is a step-up transformer that delivers high voltage to the spark plug. This value can be between 5 and 20 kilovolts (kV), depending on the working conditions. www.outdoorpowerequipment.com