No Battery? No Problem. Why Your Lawnmower (and a Dragster) Love Magnetos
- Alisa Peters
- 3 days ago
- 3 min read
Here's how little I know about magnetos: I was looking at one of our patents to help write Case Study: Redesigning a High-Output Magneto for Top Fuel Drag Racing (coming soon) , and it took me the better part of a day to realize that I was looking at the wrong patent. Facepalm. At least I knew it didn't have anything to do with X-Men. For more background on who I am and why this post exists, head over to Introduction to Alisa Learns about Magnets. To learn about magnetos, read on!
💡 TLDR: What we’re covering
What is a magneto and how does it work?
Why would you use one? (Spoiler alert: reliability and weight)
Top Fuel drag racing as a use case
In simple terms, a magneto is a self-contained electrical generator that uses permanent magnets to produce periodic pulses of alternating current. While it sounds a bit "steampunk", it's a brilliant piece of engineering because it doesn't require a battery to start or run an engine.
How It Works
A magneto operates on the principle of electromagnetic induction. When a magnet rotates near a coil of wire (or vice versa), it creates a changing magnetic field that induces a voltage in the wire. This is the opposite of an electromagnet, where you apply current to the coil which creates a magnetic field.
Most magnetos used in internal combustion engines follow a three-step process:
Generation: A rotating magnet creates a low-voltage current in a primary coil.
Interruption: A set of breaker points suddenly opens, breaking the primary circuit.
Transformation: This sudden collapse of the magnetic field induces a massive high-voltage surge in a secondary coil (the "transformer" effect). This voltage--often over 20,000 volts--is sent to the spark plug to ignite the fuel.
Why Use a Magneto Instead of a Battery?
You'll mostly find magnetos in machines where reliability and weight are the biggest concerns:
Aviation: Most piston-engine airplanes use magnetos. If the plane's electrical system or battery dies mid-flight, the engine will keep purring because the magnetos are powered by the engine's rotation, not the battery.
Small Engines: Your lawnmower, chainsaw, and many dirt bikes use magnetos. It keeps them lightweight and ensures they start even after sitting in a shed for three years with a dead battery.
Historic Cars: Before modern coil-on-plug ignition systems and heavy lead-acid batteries became the norm, magnetos were the standard for early automobiles.
Why are Magnetos used in drag race cars?
In a standard commuter car, the ignition system is designed for reliability and fuel economy. In a race car, the ignition system is pushed to its absolute physical limits. When an engine is spinning at 9,000+ RPM, the window of time to ignite the fuel becomes impossibly small. Most Top Fuel drag racers use dual magnetos and two spark plugs per cylinder. This redundancy is required because the cylinder pressure is so high that it literally snuffs out the spark. If one magneto fails, the other keeps the "bomb" timed correctly so the engine doesn't blow its cylinder heads off.
Think your project might need the reliability of a magneto? Or just a magnet assembly that can handle "impossible" conditions? Contact the real experts at QT Magnetic Solutions. (I'll be over here catching up on my comic books).
