How a Lawn Mower Armature Assembly Works

Ignition

• The armature assembly, or magneto, must receive an electrical charge to start working. That electricity comes from an ignition switch that has a relay inside it that develops a charge when two opposite-charged poles are connected. As the button is pushed or the key is turned to the “on” position, the charge travels down electrical wires that lead to the armature assembly. A broken wire or faulty switch can stop the charge from reaching the armature assembly.

Armature Assembly

• The magneto armature assembly consists of a flywheel with a magnet on it, an armature, circuit breaker and two electrical coils. The armature is attached to two coils that are stacked on top of each other. When the charge reaches the assembly, the flywheel spins the magnet around at high speed -- around 250 revolutions per minute in some engines, such as Briggs and Stratton engines. As the magnet passes the armature, electrical voltage is created. Check the flywheel to ensure the magnet is on, as they are sometimes fastened with glue.

Coils

• The armature sends the voltage through the bottom coil, typically made of copper. As the voltage travels through the coil, it gets stronger and stronger. As the voltage reaches the end of the first coil, the circuit breaker trips and shuts off the ignition. The electricity transfers to the second coil, which is wound 60 times tighter than the first coil. This makes the charge even stronger. Some charges can reach 13,000 volts before leaving the armature assembly. Broken coils can interrupt voltage creation and short out the magneto.

Combustion

• The voltage travels through another wire assembly attached to the spark plug. Once the electricity reaches the spark plug tip, it discharges into the combustion chamber. The chamber has an ignitable fuel vapor. If the air gap is set correctly, the spark breaches it and sets the vapor on fire, creating combustion for your mower’s engine. This process continues until the kill switch shuts the mower off, which will stop the flywheel from spinning.