RESISTANCE Understanding electrical resistance vs. internal resistance in power systems

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Electrical resistance and internal resistance both influence the functionality of electrical systems but serve different roles. Both types of resistance impact circuit behavior, energy efficiency, and performance.

Electrical resistance and internal resistance both affect how electrical systems function, but they serve different roles. Understanding the distinction helps when designing circuits, selecting components, or troubleshooting performance issues. Resistance primarily deals with current flow in circuit elements, while internal resistance influences power source efficiency.

What is resistance?

Resistance refers to the opposition to current flow in external circuit components. It follows Ohm’s Law, where resistance (R) equals voltage (V) divided by current (I). The material, length, and cross-sectional area of a conductor determine its resistance. For example, a long, thin wire has more resistance than a short, thick one.

Resistors are designed to control current flow, divide voltage, and dissipate power as heat. They come in different types, such as fixed, variable, and thermistors, each serving specific roles in electronic circuits. Resistance also plays a role in protecting circuits by limiting excessive current, which prevents overheating and component damage.

All materials resist current flow to some degree. However, when it comes to resistance, most materials fall into one of two categories: insulators or conductors.

• Conductors: These are materials that offer little resistance by allowing electrons to move freely. Examples of conductors include copper, gold, and aluminum.

• Insulators: These are materials that have high resistance by restricting the flow of electrons. Examples of resistors include glass, wood, and rubber.

Factors that affect resistance

The resistance of a material can be affected by various factors including temperature, length, and the cross-sectional area.

• Length: Resistance is directly proportional to the length of the conductor. Longer conductors have higher resistance

• Cross-sectional area: Resistance is inversely proportional to the cross-sectional area. Thicker wires have lower resistance than thinner wires of the same material.

• Temperature: Generally, resistance increases with temperature for conductors. (However, the effect can vary for different materials, with semiconductors typically showing decreased resistance at higher temperatures.)

What is internal resistance?

Internal resistance refers to the resistance within a power source, such as a battery or generator. In other words, it’s the name given to a property of components where their primary function is not to act as a resistor but does so anyway.

Internal resistance results from the materials used in electrodes, electrolyte resistance, and internal connections. Unlike external resistance, which is deliberately added to circuits, internal resistance is an inherent property that can’t be eliminated but can be minimized.

A lower internal resistance improves efficiency by reducing energy loss inside the power source. In batteries, internal resistance depends on factors like electrolyte composition, electrode design, and the state of charge. Over time, chemical reactions within the battery can increase internal resistance, reducing efficiency and shortening battery lifespan.

INTERNAL RESISTANCE

How internal resistance affects battery performance

Factors that affect internal resistance

Similarly, the internal resistance of a power source can be affected by various factors. These include surface area, the distance between electrodes, and battery issues.

• Electrode surface area: The larger the electrode surface area is, the lower the internal resistance will be.

• Distance between electrodes: Greater separation between electrodes leads to higher internal resistance.

• Battery factors: Longer use leads to increased internal resistance due to factors like electrolyte loss, plate corrosion, and active material shedding. Meanwhile, the charge level of the battery and properties related to designs, materials, and manufacturing processes result in varying internal resistances.

Comparing resistance vs internal resistance

One of the main differences between the two is the location where each type of resistance occurs. Resistance is found in wires, resistors, and circuit components, while internal resistance is inside the power source itself. Measuring them also requires different methods.

Resistance is directly measurable with an ohmmeter, which applies a small voltage and measures the resulting current. Internal resistance, however, is usually determined indirectly by comparing open-circuit voltage to loaded voltage or using AC impedance techniques. Electrochemical impedance spectroscopy (EIS) is often used for precise measurement, especially in battery research and diagnostics.

Internal resistance significantly affects performance, particularly in batteries. As the current increases, the voltage at the battery terminals drops due to the internal resistance. This drop reduces the available power for the connected load.

Additionally, power loss inside the battery follows the equation P = I²r, meaning higher currents generate more internal heating. Excessive heat can degrade the battery’s lifespan and efficiency over time. In high-drain applications, such as electric vehicles, high internal resistance can cause reduced acceleration, increased charging times, and lower overall efficiency.

External resistance, on the other hand, determines how electrical energy is distributed and used. It influences circuit behavior by affecting voltage drops and current flow. In practical applications, engineers use resistance to design voltage dividers, sensors, and heating elements.

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Variability of internal resistance

Unlike most external resistances, which remain relatively stable, internal resistance changes with temperature, charge level, and battery aging. Lower temperatures increase internal resistance, reducing power output. As batteries degrade, internal resistance rises, making them less efficient and more prone to voltage drops under load.

In power electronics design, minimizing internal resistance should therefore be a priority. High-performance batteries use materials and designs that reduce internal resistance, improving energy delivery. For example, lithium-ion batteries use highly conductive electrolytes and optimized electrode materials to achieve lower internal resistance.

For circuits, selecting components with appropriate resistance ensures proper current flow and voltage distribution. Power engineers should carefully choose resistor values to balance power dissipation and signal integrity. Managing both types of resistance effectively leads to more efficient and reliable electrical systems.

Understanding the difference between electrical resistance and internal resistance helps when working with circuits and power sources. Resistance controls current flow in external components, while internal resistance affects a power source’s efficiency and performance.

Internal resistance is especially important in applications like batteries and power supplies, where efficiency and energy loss matter. Proper management of resistance improves performance, reduces energy waste, and extends the lifespan of components and power sources.

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