A capacitor reduces arcing at magneto ignition points.

Why Capacitors Keep Magnetos Calm (A Gentle Guide to Arcing and the Points)

If you’ve ever poked around a small aircraft ignition system, you’ve probably heard about magnetos, the spark that starts an engine, and the tiny drama that happens at the points when they open. Here’s the short version you’ll feel in real life: when the points open, voltage spikes can cause arcing. A little component tucked in there—called a capacitor—helps smooth things out. The correct answer to “What component in a magneto reduces arcing at the points?” is Capacitor. Let me explain why that tiny part matters so much.

A quick tour of the magneto’s job

Think of a magneto as its own little power company. No battery needed for a basic ignition setup; the magneto spins and generates electricity, enough to fire a spark plug at just the right moment. Inside the magneto, you’ve got a primary circuit that carries current to an ignition coil. When the points are closed, current flows through the primary windings. When they open, the magnetic field collapses, and a high voltage surge is produced in the secondary winding—that surge becomes the spark that jumps the gap at the spark plug.

But here’s the snag: that moment of opening is a chaotic moment for electricity. The energy in the magnetic field wants to run away, and without a buffer, the contact points take a beating from arcing—the little electric fireworks right at the contacts. That arcing wears the points, can foul timing, and makes the spark less reliable. It’s not a glamorous problem, but it’s a real one in the world of aviation maintenance.

Enter the capacitor—the quiet, understated hero

In many magneto designs, a capacitor is connected across the ignition points. When the points are closed, the capacitor charges up. When the points open, rather than causing a sharp voltage spike that zaps across the contact faces, the capacitor provides a controlled path for the current. The sudden change in current is softened, the arc at the points is reduced, and the dwell time for the spark becomes more stable. The result? Longer point life, more consistent ignition timing, and a smoother engine rhythm.

To put it in a more tangible way: imagine you’re driving on a winding road, and a sudden jolt hits your steering when you hit a bump. The capacitor acts like a shock absorber, taking the edge off that jolt so the wheel doesn’t jerk and the ride stays even. In the magneto, that “shock absorber” role translates into less wear at the contact points and a crisper, more reliable spark at the moment of ignition.

How arcing actually happens (and why a capacitor helps)

Here’s the core sequence, simplified but accurate enough for practical understanding:

• The points are closed and current flows through the primary winding.

• The cam opens the points, interrupting the current.

• The collapsing magnetic field in the coil generates a high voltage in the secondary winding.

• This high voltage would normally spike across the gap where the points open, creating an arc and possibly eroding the contacts.

The capacitor sits right across the points. When the points begin to separate, the capacitor provides a competing current path. It absorbs part of the energy that would otherwise surge across the contacts. This has a couple of consequences:

• It reduces arcing at the point contacts, so the points last longer.

• It helps maintain a cleaner, more stable discharge into the primary circuit, which can sharpen the spark in the secondary.

• It contributes to more consistent ignition timing, which translates into steadier engine performance, especially at higher RPMs or under load.

The other players in the scene—what they do and why they aren’t doing this job

You might be familiar with a few other electrical components in ignition systems, and it’s helpful to know why they don’t replace the capacitor’s job here:

• Diode: Diodes are one-way traffic directors. They’re great for steering current, but they don’t smooth out the nasty voltage spikes that occur when the points open in a magneto. They’re not meant to absorb the energy like a capacitor does in this context.

• Resistor: A resistor limits current, sure, but it doesn’t store energy or provide a burst of current when the points open. It mainly calms things down in a circuit where you want to reduce current for a load or some signaling path, not to smooth fatal spikes in the ignition primary.

• Coil: The coil is the heart of the high-voltage generation, the place that does the heavy lifting for the spark. It does its job in creating high voltage, but it doesn’t quiet the arcing at the points. The capacitor’s job is more about protecting the contact interface itself rather than changing the core spark energy.

Stray tangents that illuminate the topic (and then come back to the point)

If you’re digging into Jeppesen Powerplant topics, you’ll notice that ignition systems sit at an intersection of timing, chemistry, and electricity. The capacitor isn’t flashy, but it’s a classic example of how a small, well-placed component can improve reliability dramatically. It’s the same mindset you’ll see in other aircraft systems: a little bit of correct sizing, placement, and connection can cut wear, reduce maintenance headaches, and keep an engine running smoothly under varying conditions.

A quick mental model you can carry around

• Points act like switches in a high-speed relay. When they open, the energy wants to jump across.

• The capacitor acts like a small buffer battery in parallel with the switch. It charges when the switch is closed and releases some of its energy when the switch opens.

• The result is a gentler transition, less spark leakage at the contacts, and a more consistent spark to the plug.

Real-world signs a capacitor matters

• You’ll notice more wear on the points if the capacitor is absent or failing.

• Rough running or misfires at certain RPM bands can be a telltale sign of ignition irregularities.

• Inconsistent spark timing may show up as rough starts or uneven idle.

If you’re involved in maintenance, a practical approach is to inspect the capacitor’s condition and its connection across the points. Look for signs of swelling, leakage, or corrosion at the terminals. A capacitor that’s tired or damaged won’t absorb energy as intended, and arcing can creep back in.

A few concise takeaways

• The capacitor across the ignition points is the tool that minimizes arcing in magnetos.

• It stores a little energy and releases it at the critical moment, smoothing the transition when the points open.

• Other components like diodes, resistors, and coils play essential roles in broader electrical systems, but they don’t perform the same arc-suppressing job the capacitor does in this specific setup.

• Maintenance-minded pilots and technicians keep ignition systems reliable by paying attention to capacitor health and proper wiring across the points.

A final thought to keep curiosity alive

Ignition systems are a great reminder that aviation tech blends elegance with practicality. You don’t need a giant gadget to solve a stubborn problem—you need the right part placed in the right place, at the right moment. The capacitor’s role in a magneto is a perfect example of that principle in action. It’s a small component with a big impact, quietly keeping the spark reliable so the engine can sing through takeoffs, climbs, and cruising legs without an unnecessary hiccup.

If you’re exploring the world of magnetos and ignition systems, that capacitor across the points is a useful spotlight. It’s a reminder that a lot of aviation’s reliability comes down to thoughtful, precise engineering—where even a tiny part can make a meaningful difference in performance and safety. And yes, that little capacitor is one of those unsung heroes you’ll come to appreciate as you dive deeper into Powerplant topics.