In the car’s ignition system, coils are essential for the spark production to ignite the air-fuel mixture. These spirals of wire are generally of two types: resistor and non-resistor. The most common differences between these are their internal resistance and voltage management. Today, I will discuss resistor coil vs. non-resistor coil to help you choose between them.
In short, resistor coils often have an external or special resistor wire to regulate the current. They act as a simple but efficient regulator (1). Alternatively, non-resistor coils need no external component. It implies that the resistor is built into the coil. They aim to limit the current to the points and prevent burning (2).
The rest of the article contains detailed information like both resistors’ features, benefits, applications, etc. I will also include more necessary things to get a transparent idea regarding these coils. I hope you have a couple of minutes to read the whole content.
A Brief to Coils in a Car
Talking about physics and engineering, you will find a lot of discussions about coils. Well, the term “coil” means a series of loops (3). Its function is known as electromagnetic induction. But do you know how these coils work?
An electric current passing through the coil creates a magnetic field around the loops. Then, the coil and magnetic field interaction induces a current in the wire. For sure, it works as a basis for many electric and electronic devices.
You may find coils in many devices like transformers, inductors, and motors. There are two coils in transformers: primary and secondary. In electric motors, magnetic fields are generated to interact with the permanent magnets’ fields. They can convert different forms of energy.
The ignition coil often has an integrated spark plug wire for vintage motorcycle engines. They are significantly out-of-spec in terms of ohms (e.g., 8,000 ohms). As a result, they can impact spark delivery and engine performance (4).
Now, let’s know about resistor and non-resistor coils.
Resistor Coils: Internal Control
In this part, you will learn many things regarding the resistor coil.
Definition
Like its name, it incorporates a built-in resistor element within its design (5). It resists the flow of electricity or electric current to the points. In this way, a resistor coil can prevent the current from consistently handling a full 12v source and burning out. Likewise, these components are wired or integrated within the coin itself (1, 2).
Versatility
These coils can either have an external resistor or have the resistor built into the coil. In the case of an external one, it is often a white ceramic or a special wire in the loom. However, resistor coils are made up of a conductor length. You can choose from multiple sizes of these coils (for instance, as small as 1/8 watt and just 2mx1.5mm in electronics).
Functionality
If you choose the wrong resistor cap or coil type, the high resistance may choke off power to the spark plug. It causes a weak spark and potentially leads to engine misfires.
By introducing resistance, the voltage across the coil is reduced. According to Ohm’s Law, it influences the current flowing through the coil. I guess you know about this law (I = V/R).
Impact of the Resistor Coils
Why should you use resistor coils? Well, the presence of the resistor restricts the initial surge of current when the coil is activated. You can get a better engine start-up. It safeguards the ignition system from excessive current strain.
Applications
Resistor coils are standard in multiple applications. For example, traditional car ignition systems have these coils. Some starter motors utilize resistor coils. They manage the initial current surge during engagement with the flywheel. Again, modern electric toasters, ovens, cooktops, space heaters, hot water systems, and bathroom heat lamps also have resistor coils.
Hence, resistor coils ensure the system operates within its intended parameters. You can also get these coils in voltage-sensitive circuits. They protect the circuits by regulating the current flow to maintain a balanced voltage level. It prevents potential damage caused by voltage spikes.
Non-Resistor Coils: Direct Power Delivery
Feeling interested? Don’t worry; I will discuss the counterparts, too.
Definition
So, the basic thing is that non-resistor coils do not have the internal resistance element. These coils deliver a more powerful spark energy (6). Likewise, the design of non-resistor coils provides more robust ignition and better engine performance.
Versatility
Suppose your vehicle has non-resistor coils yet needs a resistor coil. In that case, it may cause abnormal combustion, idling, and high-RPM misfire. Anyway, you can see these coils in older vehicles. In these applications, the more vital spark is always essential. Still, they can cause interference with other electronic components. It is because the powerful spark energy they produce can generate electrical noise.
Functionality
As I said, non-resistor coils do not have any internal resistor. This design of the direct connection to the power source enables unrestricted current flow through the primary circuit. However, this flow produces a more rapid build-up of the magnetic field within the coil. As a result, the engine can produce a stronger spark.
Impact of the Non-Resistor Coils
The solid spark offers improved engine performance. You can use these coils if you need optimal combustion. The magnetic field can offer faster engine response and higher RPM capabilities in certain racing or modified engines.
Applications
Most automobile experts suggest using resistor coils for most vehicles. But when a stronger spark is paramount, non-resistor coils work the best. Hence, many of us have heavily modified engines for racing or competition. In these cases, a non-resistor coil can offer a marginal benefit due to the faster build-up of the magnetic field.
Common Issues with Resistor & Non-Resistor Coils
While researching this topic (resistor coil vs. non-resistor coil), I have found some heated discussions (7,8,9).
| Resistor Coil Issues | Non-Resistor Coil Issues |
| Overheating: Resistor coils generate heat due to resisting electric flows. You need to manage it properly. | Interference: Well, non-resistor coils can cause interference with other electronic components in a vehicle. |
| Wear and tear: These coils can wear out over time and cause a decrease in performance and, eventually, failure. | Misfires: Like resistor coils, these things can cause the vehicle to experience misfires and reduce gas mileage. |
| Power surges: Power surges can damage these resistor coils. | Starter failure: You may sometimes face difficulty in vehicle starting. |
| Engine misfires: Faulty coils may cause engine misfires, a rough idle, and a loss in power and acceleration. | Damage: In the absence of a resistor, they can damage other components in the vehicle. |
| Failure to start: Sometimes, a defective component fails to produce a spark properly. It prevents the vehicle from starting. |
Things to Consider While Choosing Resistor and Non-Resistor Coils
Which coil should you choose between two types of coils? Basically, you need to understand the vehicle or engine requirements. According to my knowledge and observations, you can keep these factors in your mind:
Vehicle Specs
After all, you must check the manufacturer’s specifications for your vehicle. But why? Well, some vehicles work with resistor coils and others need non-resistor ones.
Engine Performance
For better engine performance, you can choose non-resistor coils as they provide a stronger spark. But they can cause interference with other vehicle parts.
Durability
Always consider the durability and longevity of any coil you choose. For example, resistor coils generate heat and require frequent replacement due to wear and tear.
Cost
Want to save money? You can use non-resistor coils. However, you can select resistor coils if you do not have sufficient time to maintain them.
Ignition System Compatibility
The compatibility of coils with ignition systems varies. For instance, PerTronix Ignitors require coils with specific internal resistance values depending on the engine type (10). Then, coils used with MSD Ignitions must meet specific resistance criteria to be compatible (11).
Final Words
General Motors (GM) vehicles transitioned from using a 6-volt non-resistor ignition coil to a 12-volt externally resisted coil in 1955. This practice continued until 1975. Vehicles newer than 1963 required an additional resistance unit (12). So, that was the beginning of the debate: resistor coil vs. non-resistor coil.
However, I have explained that both coils are famous for their resistance and applications. You can choose the right one for your vehicle if you have read the article thoroughly. And I hope you loved reading it.
Thanks for your time.
