Does a Spark Plug Use AC or DC? And What Voltage Is Used

Spark plug photo

A spark plug produces an electric spark to ignite the engine. It draws a high voltage current to generate that spark in the engine, drawing electricity regularly. Time to look into electricity flow in the spark plugs.

So, does a spark plug uses AC or DC? A spark plug uses the vehicle’s battery, which is DC, as its power source. The ignition coil uses the battery’s DC and converts it into a high voltage pulse and then feeds it to the spark plug via a distributor.

Then what voltage is used in the spark plug? Usually, the high voltage electricity in the spark plug will be around 15,000 to 20,000 volts. In modern spark plugs, the voltage can be as high as 60,000 volts depending on the design and the model.

While the answer may seem straightforward, there are lots of nuances that are missed here. Let’s dig deep to understand how the electricity flows in the spark plug.

A Spark Plug Draws AC or DC?

Spark plugs receive high voltage current from the ignition coil, which uses the battery’s DC as its power supply.

So, in a way, the battery’s DC power is the source of power for the spark plug. Be it in a motorcycle or in a car.

But the electricity flow is not that straightforward though. The direct current from the battery is of low voltage (usually 12 volts). And spark plugs require around 15,000 to 20,000 volt current to ignite the engine.

So, how does a spark plug get such high voltage from the battery which provides a low voltage current?

Enter ignition coil.

The ignition coil acts as a transformer and uses the low voltage current from the battery to generate (convert to be precise) to high voltage pulses and pass it onto the spark plugs via a distributor.

Diagram of Ignition (Induction) coil

Essentially, while the battery is the power source for the spark plug, it is the ignition coil that generates the required high voltage current to produce the electric spark.

As for the question, does the spark plug use DC or AC? A spark plug uses the vehicle’s battery, which is DC, as its power source. The ignition coil draws up the battery current to convert it into a high voltage pulse and then feeds it to the spark plug.

I know it’s still confusing. So, let’s discuss the flow of electricity from the battery to the spark plugs in a bit more detail.

The Flow of Electricity in Spark Plugs

Spark plug sparking illustration

As usual, the current flow starts from the source – the vehicle’s battery. For both motorcycles and cars, the battery acts as the power source here.

The direct current from the battery flows to the ignition coil first. Ignition coil, right. Let’s deep dive into this one.

The ignition coil is an induction coil. This coil transforms the battery’s low voltage, direct current supply into a high voltage supply needed to create an electric spark. This electric spark in the spark plug will finally ignite the fuel.

That’s why, the ignition coil (or the induction coil, whatever you prefer to call it) is essentially a high voltage transformer.

This transformer is made up of two coils of wire, namely – the primary coil and the secondary coil. Let’s get a bit technical here and understand the working of the ignition coil.

The two coils are both wrapped within the transformer. The primary coil is usually the outer coil with a larger diameter whereas the secondary coil is wrapped at a lower radius typically around a rod. Also, the secondary coil has hundreds of more turns of wire than the primary.

The direct current from the battery flows from the battery terminals to the primary coil. This current flow in the primary coil is controlled by the breaker points or a solid state device depending on the electronic ignition system.

So, when the current in the primary coil is broken by the breaker points, the magnetic field by the primary coil collapses. As a result, the secondary coil is engulfed in a changing powerful magnetic field. This induces a current in the secondary coil.

Hey, that sounds like electromagnetic induction! You bet it is.

This induced current in the secondary coil is a high voltage current due to the high number of wire windings in the secondary coil. That’s how a high voltage pulse is generated for the spark plug ignition.

Next, this high voltage current is passed onto the distributor through insulated high voltage wires. The distributor then passes the high voltage to the appropriate spark plug.

Phew, that’s a long explanation!

Let me try a short and confusing one.

So, in short, the low voltage current supply from the battery is transformed into a high voltage pulse in the ignition coil (induction coil). This high voltage pulse is passed from the coil to the distributor which then passes on to the spark plugs.

What Voltage Does a Spark Plug Need?

Spark plug illustration

Typically, a spark plug needs a high voltage of 15,000 to 20,000 volts to generate the electric spark in the engine.

In modern spark plugs, the voltage can be as high as 60,000 volts depending on the design, spark plug type, and vehicle model.

The high voltage requirement changes based on the vehicle used as well as the spark plug types – copper, platinum, double platinum or iridium spark plug.

Modern automotive spark plugs generate a far higher voltage spark than the old ones. The old spark plugs operated with a voltage of 10,000 volts. The modern spark plugs operate as high a voltage as 60,000 volts.

A high voltage spark has its advantages. Simply put, a high voltage spark allows for a more energetic and complete ignition. The sparks generated are hotter, larger, and longer-lasting.

One of the main reasons modern spark plugs can operate at such high voltage is the improvements on the insulator part of the spark plug.

Two major technological improvements to the insulator include i) using sintered alumina as the insulating material; ii) the addition of ribs to the insulator.

Sintered alumina has good thermal properties as well and can withstand high temperatures. The addition of ribs improved the electrical insulation further.

These technological improvements have resulted in modern spark plugs generating high voltage sparks (as high as 45,000 to 60,000 volts) in engines.

Can a Spark Plug Work Without the Battery?

Since the battery is the power source for the spark plugs in modern automobiles, a spark plug will NOT work without a battery.

Without the battery functioning in a motorcycle or even in a car, almost all the accessories, circuits, and electronic systems will not work at all.

Forget spark plugs, without the battery, the motorcycle will not even start!

So, yeah. A battery is essential for the spark plug to work. And without the battery, the spark plug will not receive its high voltage current to ignite the spark in the engine.

To Summarize

Spark plugs receive high voltage current from the ignition coil, which uses the battery’s DC as its power supply.

But, the battery is of 12V and the spark plug needs a high voltage in the range of 15,000V to 20,000V.

And that’s where the ignition coil (also called induction coil) fits in.

The ignition coil acts as a transformer and uses the low voltage current from the battery to convert it to high voltage pulses and pass it onto the spark plugs via a distributor.

Essentially, the low voltage current supply from the battery is transformed into a high voltage pulse in the ignition coil. This high voltage pulse is passed from the coil to the distributor which is then passed on to the spark plugs for spark ignition in the engine.

Typically, a spark plug needs a high voltage of 15,000 to 20,000 volts to generate the electric spark in the engine.

Also, the battery is essential for the spark plug to work. Without the battery, the spark plug will not receive its high voltage current to ignite the spark in the engine.