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How to Measure Internal Resistance of Batteries: Methods and Implications - DonosHome - OBD2 scanner,Battery tester,tuning,Car Ambient Lighting

How to Measure Internal Resistance of Batteries: Methods and Implications

Internal resistance is a crucial parameter when assessing the health of a battery. Particularly in nickel-based systems, a high internal resistance reading can signal the end-of-life for the battery. However, it's important to note that resistance measurement alone is not the sole performance indicator. In the case of lead-acid batteries, there can be variations of 5–10 percent between batches, especially in stationary units. Therefore, the most effective use of resistance measurement is tracking changes within a specific battery from installation to retirement.

Internal Resistance and Battery Health

Contrary to a common misconception, internal resistance is not directly linked to a battery's capacity. Modern lead-acid and lithium-ion batteries exhibit a relatively stable resistance throughout their service life. Improved electrolyte additives have minimized internal corrosion, also known as parasitic reactions, on the electrolyte and electrodes.

It's crucial to understand that resistance measurements do not provide insight into the overall health of a battery, as resistance often remains constant with use and aging.

Understanding Impedance

Before delving into methods of measuring internal resistance, it's essential to differentiate between pure resistance (R) and impedance (Z). While R represents pure resistance, Z includes reactive elements like coils and capacitors. Both are measured in ohms (Ω), a unit established by the German physicist Georg Simon Ohm.

Most electrical loads have reactive components, including capacitive and inductive reactance. Batteries, with resistance, capacitance, and inductance, are best described using impedance. The Randles model, comprising resistors R1 and R2, as well as capacitor C, illustrates impedance in batteries.

Measurement Methods

Several methods exist for measuring internal resistance, each with its advantages and limitations.

DC Load Method

This traditional method involves briefly discharging the battery and measuring the voltage drop. While accurate for large stationary batteries, it has limitations in differentiating between internal resistance components. It provides only ohmic references and does not account for state of charge or capacity estimations.

Two-Tier DC Load

This method involves sequential discharge loads of different currents and durations, offering additional information about the battery. However, like the traditional DC load method, it provides only resistive values.

AC Conductance

Conductance measurement, often used for starter batteries, injects a frequency to minimize reactance. AC conductance meters are common in garages for measuring Cold Cranking Amps (CCA). The 1,000Hz ohm test is another variant providing different values compared to DC methods, catering to specific applications.

Electrochemical Impedance Spectroscopy (EIS)

Primarily used in research laboratories, EIS measures R1, R2, and C separately, allowing for state-of-charge and capacity measurements. However, it requires expensive equipment and expertise.

Conclusion

Choosing the appropriate method for measuring internal resistance depends on the battery type and intended application. While traditional methods like the DC load remain reliable, newer techniques like EIS offer more detailed insights, albeit with higher costs.

 

Vorheriger Artikel Comment Fonctionnent les Batteries au Plomb-Acide dans les Tendances Actuelles de l'Industrie des Batteries | FR

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