Does an ignition coil need 12 volts?

An ignition coil is a crucial component in any gasoline-powered internal combustion engine. Its role is to transform the 12 volts from the vehicle’s battery into the thousands of volts needed to create an electric spark that ignites the air-fuel mixture in the engine’s cylinders. This sparks allows for combustion which powers the engine. So in short, yes an ignition coil does need 12 volts to function properly.

What is an ignition coil?

An ignition coil is a type of transformer with some similarities to a Tesla coil. It consists of two coils of wire wrapped around an iron core. The primary coil has a few turns of heavy gauge wire and is connected to the vehicle’s 12 volt battery. The secondary coil has many more turns of finer gauge wire and is connected to the spark plugs.

When power flows into the primary coil from the battery, a magnetic field builds up in the iron core. When this power is cut off by the ignition system, the magnetic field collapses very suddenly. This induces a high voltage in the secondary coil, typically between 20,000-50,000 volts. This spark jumps across the gap in each spark plug, creating the combustion needed to drive the pistons.

The role of the 12 volt supply

The 12 volt supply from the vehicle’s battery provides the power that gets transformed into the high voltages needed for the spark plugs. Without this 12 volt supply, no power would flow into the primary coil so no sparking could occur.

Most modern vehicles have 12 volt electrical systems, this has been the standard for decades. So ignition coils are designed to work specifically with a 12 volt input. Some large trucks or older vehicles used 6 volt systems, so the ignition coils were designed differently to work with 6 volts instead.

The ignition coil doesn’t need the full capacity of the battery. It only draws less than 5 amps in most applications. But it does need a minimum of around 11 volts to properly transform up to the high secondary voltage. At lower inputs, performance declines.

What happens without 12 volts?

If an ignition coil doesn’t receive 12 volts, several problems can occur:

– Weak or non-existent spark to the spark plugs. This prevents combustion.

– Hard starting of the engine, needing cranking for longer periods.

– Misfiring at higher RPMs as demand increases.

– Backfiring or sputtering as unburned fuel ignites in exhaust.

– Stalling, especially under acceleration as demand exceeds supply.

– Poor fuel efficiency due to incomplete combustion.

– Difficulty idling smoothly, idling high or stalling.

– Engine overheating from lack of smooth combustion.

– Difficulty revving or throttling up smoothly.

– Flashing of the ‘check engine’ light with cylinder misfire codes.

So in summary, without the proper 12 volt supply the ignition system can’t reliably deliver the strong, well-timed sparks needed for smooth engine operation.

Causes of low/no voltage to the coil

There are a few potential causes if an ignition coil is not receiving 12 volts:

– Battery not charged properly – A low or dead battery due to old age, loose terminals, defective alternator etc.

– Loose or corroded wiring – Connections in the starter or ignition system have become loose or corroded.

– Faulty ignition switch – Not delivering full power to ignition system.

– Blown fuse – The fuse for the ignition coil or general ignition system may have blown.

– Faulty relay – If equipped, a defective relay disrupts power flow to the coil.

– Resistance in circuit – Excess resistance in the wiring prevents proper voltage from reaching coil.

– Faulty trigger signal – Coil needs a proper signal from points, PCM etc to operate.

– Open circuit – A break in the wiring that feeds the coil.

So in most cases, a loss of the 12 volt supply is due to a fairly simple wiring, fuse or component fault rather than a failure of the coil itself. Proper diagnosis and test should pinpoint the root cause.

Importance of proper primary resistance

Along with voltage, sufficient amperage is also required to generate a strong spark. The ignition coil needs very low resistance in the primary winding so current can flow easily with 12 volts applied. Typical primary resistance is just 0.3-2 ohms in most coils.

If the coil’s primary resistance is too high, the primary current flow will be restricted, resulting in a weak spark. Causes can include:

– Dirty, corroded or oxidized contacts

– Loose wiring connections

– Damaged primary winding

– Leaking coolant/moisture into coil

Using an ohmmeter to measure primary resistance can identify if it is out of spec and causing voltage to be lost.

Significance of secondary resistance

The secondary winding of an ignition coil has a very high resistance, typically 6,000-30,000 ohms. This is needed to allow the high secondary voltage to develop. When combined with the large ratio of secondary to primary winds, the high resistance transforms the 12 volts up to the required high voltage spark.

Measuring secondary resistance with an ohmmeter is one way to test for a defective coil. An open circuit or short means it won’t develop the required high voltage due to a damaged secondary. Typical specs are 8-15K ohms for coils under 50K volts and up to 30K for coils over 50K volts.

Results of insufficient coil voltage

As covered earlier, an ignition coil starved of the required 12 volts can’t do its job properly. Symptoms would include:

– Hard starting, long cranking before starting

– Misfires, backfiring, sputtering

– Lack of power, acceleration and performance.

– Surging or erratic idle.

– Stalling or dying when revved.

– Excessive fuel consumption.

– Flashing check engine light, cylinder misfire codes.

– Smoke and backfires in exhaust.

– Unburned fuel foul and contaminate spark plugs.

– Potentially catastrophic engine damage from pre-ignition or detonation.

So an ignition system with inadequate coil voltage risks immediate performance issues plus long term engine damage if left unchecked. Proper diagnostics and repair should be done promptly.

Typical specifications

While there is some variation, here are some typical specifications for ignition coils:

– Input voltage: 12-14 volts

– Primary resistance: 0.3-2 ohms

– Secondary resistance: 6,000-30,000 ohms

– Turns ratio: 75-150:1

– Secondary output: 20,000-50,000 volts

– Spark plug gap: 0.028-0.060 inches.

Measuring volts, resistance and spark gap can determine if coil is operating within design specs or has failed.

Coil-on-plug vs. coil pack ignition systems

Modern engines use either coil-on-plug (COP) or coil pack ignition systems. COP coils sit right on top of each spark plug. Coil packs have one coil supplying 2, 3 or 4 cylinders via short leads.

But both systems essentially work the same. Within each coil, the 12 volts flow through the primary winding to induce high voltage in the secondary. This sparks the plug.

Multiple COP coils or packs are controlled by the Powertrain Control Module (PCM) to fire the plugs in the proper sequence. Voltage requirements are the same whether COP or coil pack.

Conclusion

In summary, an ignition coil absolutely needs 12 volts supplied to its primary winding in order to induce the 20-50,000 volts needed to fire the spark plugs. Without proper 12 volt supply, the coil and ignition system can’t function, leading to poor performance, misfires and potential engine damage.

Testing resistance and voltage at the coil along with inspecting wiring and connections can diagnose defects preventing proper voltage supply. Any problems should be addressed promptly to restore smooth operation.

While the era of points and condenser ignition systems is over, the modern coil still needs 12 volts just like vintage coils. An efficient, reliable power supply to the coil remains the lynchpin for delivering intense sparks and keeping engine performance where it should be. So always check coil voltage when diagnosing ignition issues.

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