DC Internal Resistance: The Total Resistance in a Battery
DC internal resistance is the total resistance inside the battery, measured by discharging or charging the battery at a constant current. This test evaluates all the resistances within the battery, including ohmic resistance, interfacial impedance, charge transfer impedance, and diffusion impedance. The formula for calculating DC internal resistance is based on Ohm’s law:
R = (V0 - Vt) / Ip
Where:
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V0 is the initial voltage of the battery.
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Vt is the voltage after applying a pulse.
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Ip is the applied current.
This method provides a snapshot of the overall internal resistance that impacts battery performance during regular discharge or charge cycles.
AC Internal Resistance: The Resistance Measured at High Frequency
Unlike DC resistance, AC internal resistance is measured by injecting an alternating current signal into the battery and observing the resulting voltage signals. AC impedance is a part of the impedance spectrum, which can be graphed as semi-circles at various frequencies.
At high frequencies, AC internal resistance primarily reflects ohmic internal resistance, which is the basic resistance that doesn’t change with frequency. This is because at high frequencies, capacitors in the battery block lower frequencies, leaving only the resistance component to be measured.
Key Differences Between DC and AC Internal Resistance
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DC Internal Resistance measures the sum of all impedances inside the battery, including the ohmic resistance, charge transfer, and other electrochemical factors.
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AC Internal Resistance, particularly at high frequencies, mainly measures the ohmic resistance. At lower frequencies, there’s a linear relationship between AC and DC resistance, allowing AC measurements to indirectly reflect overall internal resistance.
Why Choose AC Internal Resistance for Battery Sorting?
Efficiency: DC internal resistance testing requires longer setup times and more equipment, whereas AC internal resistance is faster and more convenient for testing large volumes of batteries.
Cost-Effectiveness: DC testing requires complex charging and discharging setups, increasing testing costs. AC testing, on the other hand, is more cost-effective with simpler equipment.
Relevance: Although AC internal resistance only measures the ohmic resistance, its strong correlation with DC internal resistance makes it an effective tool for evaluating battery performance, particularly in sorting and production stages.
Conclusion: A Comprehensive Approach to Battery Performance
Both DC and AC internal resistance tests provide valuable insights into battery health, with each method serving specific purposes. For high-volume testing and sorting, AC internal resistance is preferred due to its efficiency, simplicity, and cost-effectiveness. However, for a more detailed analysis of battery health, especially in high-performance applications, DC internal resistance remains a critical parameter.
At Wrindu, we provide state-of-the-art testing solutions designed to measure both AC and DC internal resistance accurately and efficiently. Whether you're in production, research, or battery maintenance, our testing instruments ensure reliable results every time.
For more information on our DC and AC internal resistance testers, visit official website: www.wrindu.com / www.hvtesters.com
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