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[Visitor (58.214.*.*)]answers [Chinese ]Time :2022-11-20
The voltage curve of lithium-ion batteries can be divided into 3 stages during the whole discharge process:

1) The voltage of the battery drops rapidly in the initial stage, and the larger the discharge rate, the faster the voltage drops;

2) The battery voltage enters a stage of slow change, this period is called the platform area of the battery, the smaller the discharge rate, the longer the platform area lasts, the higher the platform voltage, the slower the voltage drop.

3) When the battery power is close to being drained, the battery load voltage begins to drop sharply until the discharge cut-off voltage is reached.

When testing, there are two ways to collect data:

(1) Collect data such as current, voltage and time according to the set time interval Δt;
(2) Collect current, voltage and time data according to the set voltage change difference ΔV. The accuracy of charging and discharging equipment mainly includes current accuracy, voltage accuracy, and time accuracy. Table 2 shows the equipment parameters of a charging and discharging motor, where %FS represents the percentage of full scale and 0.05% RD means that the measured error is within 0.05% of the reading.
Charging and discharging equipment generally uses a numerical control constant current source instead of the load resistance as the load, so that the output voltage of the battery has nothing to do with the series resistance or parasitic resistance in the loop, but only with the voltage E and internal resistance r of the ideal voltage source equivalent to the battery and the loop current I. If a resistor is used as a load, set the voltage of the battery-equivalent ideal voltage source to E, the internal resistance to r, and the load resistance to R, and use a voltmeter to measure the voltage across the load resistor, as shown in the figure above Figure 6. However, in practice, there is a lead resistance and a fixture contact resistance (unified as parasitic resistance) in the circuit, and the equivalent circuit diagram shown in Figure 6 is shown in Figure 6.In practice, parasitic resistance is inevitably introduced, which makes the total load resistance larger, but the measured voltage is the voltage across the load resistance R, so an error is introduced. Fundamentals of discharge testing..

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