On the outside, an ignition coil might just look like an ordinary piece of metal with rubber parts rubber that slides over the top of your spark plug. 

But it’s much more than that. Without one, your engine wouldn’t work at all.

In this blog post, you’ll discover:

  • Why an internal combustion engine relies on ignition coils 
  • What “electromagnetism” means
  • How ignition coils work – and the 2 most common types
  • Some ignition coil FAQs – including whether they can fail

Prefer to get this information in podcast form? Listen to the 30-Minute Motorcycling Podcast episode about ignition coils and what they do:

What Is An Ignition Coil, and Why Do You Need One?

With an ignition coil, the engine can solve a shortcoming in the design of an internal combustion engine.

Here’s the deal – the average motorcycle battery can store 12 V. However, in order for the spark to be made across the spark plug gap, it needs as much as 60,000 volts.

So, we’re about 59,988 Volts short. What can we do about this?

We could install a bigger battery, but that would fry the entire electrical system as soon as the engine starts.

Or, we could have an electronic component inserted on top of the spark plug that takes the low 12-volt input and amplifies that to the high voltage that is only needed for the spark.

This electronic component is the “ignition coil.”

To understand how this works, let’s now take a look at electromagnetism, since it’s key to understand how a seemingly small ignition coil can turn 12 Volts into 60,000 Volts.

What Is Electromagnetism (And Why Do Ignition Coils Rely On It)?

Entire books have been written on the subject of electromagnetism, but here’s how it works at a fundamental level:

Electromagnetism aims to increase the eletrical charge by using a metal coil wrapped around an iron core or by winding two separate coils on top of each other.

Once the electricity passes through this metal coil, it creates a strong magnetic field, which, in turn, creates a large amount of current.

And according to the principle of Ohm’s Law, if the current increases, so does the voltage – hence why ignition coils rely on electromagnetism.

How Do Ignition Coils Work?

We’ve just covered that “what” – now, let’s move on to the “how.”

An ignition coil consists mainly of two iron coils – one of these is called the “primary windings” and the other one is called the “secondary windings.”

As the electricity enters the primary windings, the voltage begins to increase to around 250 Volts. Then, the secondary windings amplify the voltage up to either 20,000 volts or 60,000 volts.

The reason why the coils for the second windings can create such a high voltage is because of the fact that they turn more often than the primary windings.

Does it sound confusing? Don’t worry – here’s a great video from the National MagLab YouTube channel that explains how it all works in practice:

What Are The 2 Most Common Ignition Coil Types?

Canister type

image of canister type ignition coil

This type is mostly found on older single-cylinder engine bikes with carburetors and gets its name from its metal canister shape.

The canister type tends to rely on wires to connect to the spark plug – meaning that if one or both of these wires snap, the ignition coil will stop working.

And although the canister ignition coil can produce 20,000 Volts, fuel-injected bikes require an even higher voltage of about 60,000 Volts or more.

Molded type

image of a molded ignition coil type

Out of both ignition coil types, this is the one you’re more likely to find on your bike. Compared with the canister type, there are many improvements with the molded type.

The biggest improvement is that it can develop the higher voltage that fuel-injected engines demand and that it’s more robust.

Another huge improvement is that it gets rid of the need for spark plug wires. Instead, the coil sits directly on top of the spark plug.

As long as it sits there, the spark plug will receive the extra voltage it needs.

Ignition Coil FAQs

Are ignition coils and spark plugs the same?

Although they work hand-in-hand, ignition coils and spark plugs are NOT the same thing.

The ignition coil might create the high voltage, but the spark plug is the final destination where the spark actually happens. 


Can ignition coils fail?

They may have relatively few parts, and it might not happen very often, but despite this, they can indeed fail. Some common symptoms of a failed or failing ignition coil include:

  • Engine misfiring
  • Loss of power
  • Worsened fuel economy

Are ignition coils easy to replace?

Generally speaking, yes. The main thing you want to be careful about is your battery.

Since ignition coils produce a deadly amount of current, ensure your battery is disconnected before attempting to replace an ignition coil.