Instruction d'utilisation Agilent Technologies AN 372-2

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Agilent AN 372-2
Battery Testing
Application Note
An electronic load can be used to discharge batteries of various
chemistries to determine actual capacity, capacity retention,
and internal impedance.

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Introduction Increasing demand for portable DC Whether testing batteries in R&D or power has risen from improvements production environments, the test in battery and motor design technol- requirements for each of the different ogy. More than ever before, portable battery types are basically the same. DC powered products have become Figure 1 shows a common test config- available in many diverse applications. uration. In general, the testing of a Rechargeable batteries appear in all battery involv

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Application Overview and Test Implementation 1 Seven standard test procedures are the specified minimum voltage called Rated Capacity used to verify certain electrical char- the “end of discharge voltage” (EODV). The principal measurement of a acteristics of secondary batteries: The EODV for nickel-cadmium batteries battery’s performance is its rated is typically 1.1 to 0.9 Volts. capacity. Capacity ratings are attained 1. Rated capacity in an accelerated test approximating 2. Capacity retentio

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Capacity varies with the rate of dis- Average and maximum capacities are Capacity Retention charge as shown in Figure 3. Testing obtained by putting the battery through This test characterizes how much of a for how discharge rate affects capacity five successive charge/discharge sta- fully charged battery’s capacity is is discussed later in more detail. bilizing cycles. The batteries are given retained over a long period of time Generally, lower discharge rates over five stabilizing cycles where

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The battery is given five stabilizing Impedance Test Effective Internal Impedance cycles in accordance with the previ- The battery must be fully charged as Battery impedance is dependent ously outlined procedure. outlined above. An AC current source on temperature, its state of charge, ( 1 kHz) is applied to the terminals of and the load frequency. The effective ~ Life Cycles 1 through 48 the battery. The AC current through internal impedance is lower for a fully 1. Charge 11 hours and the bat

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Many cells can be quick-charged at a One final test, called the “forced dis- Miscellaneous Tests rate up to C/3 in as little as 3 to 5 hours charge test,” determines the safety of In addition to the tests already men- instead of the standard 12 to 15 hours a battery under certain abusive con- tioned, there are also other miscella- at the C/10 rate. High rate charging ditions. This test is very dangerous neous tests performed on nickel- should be done under controlled con- because, during the tes

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Test Equipment Requirements From the various tests described The second alternative (Figure 7) shows so far, we can see some common that using a power supply may be more requirements for test equipment. All desirable because timed fast charge, the tests require a discharge cycle dump-timed charge, and forced dis- using a constant current. A constant charge tests all require a DC power discharge current cannot be attained source anyway. Additionally, a con- with a simple resistor because the stan

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