The hottest portable series battery voltage detect

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Portable series battery pack voltage detection system

1 introduction

series battery packs are widely used in communication radio, portable electronic equipment, aerospace satellites, electric bicycles, electric vehicles, ups and other fields. Generally, the performance of the single battery in the battery pack directly affects the overall performance of the battery pack. In order to improve the reliability of the battery pack, the performance of the single battery should be consistent. For important equipment, it is necessary to regularly monitor all single batteries, that is, measure the voltage of single batteries

there are many methods to measure the voltage of single battery. The simplest one is to measure the voltage of each series node in turn. Because the measured voltage is the total voltage, and the voltage of single battery only accounts for a part, the measurement accuracy will be reduced in proportion; Another measurement method is to use an isolated operational amplifier for each single battery. This operational amplifier can convert the battery voltage into a unified reference ground voltage, and avoid the problems of drift error and leakage current caused by resistance partial voltage. However, it is large and expensive, and is only suitable for those occasions that require high measurement accuracy and do not consider leakage current and cost. In addition, the third method is to use relay array selection for measurement, which is complex to control the switch. At present, operational amplifier differential amplification method and direct sampling method are widely used in voltage measurement, but these methods have the disadvantages of complex circuit and large volume, and they have certain limitations when applied to those fields that require volume and weight. Therefore, this paper proposes a measurement method using ordinary optocoupler instead of linear optocoupler, and a portable series battery voltage detection system with C8051F410 embedded MCU as the core

2 working principle of the system

portable series battery voltage detection system is composed of battery voltage conversion circuit, C8051F410 single chip microcomputer and LCD liquid product display, as shown in Figure 1

2.1 principle of battery voltage conversion

the battery voltage conversion circuit is shown in Figure 2. The conversion circuit is composed of Southern ordinary optocoupler TLP and operational amplifier A1. The resistance RB is the sampling resistance, and the capacitance cn is used to improve the anti-interference ability

in Figure 2, TLP is selected as the optocoupler, LM324 as the operational amplifier, ra=5 K Ω as the input resistance, and rb=1 K Ω as the sampling resistance. The curve of experimental food contact materials and products under normal use conditions is shown in Figure 3. The standard voltage is the measured value of Agilent 34401

the system adopts embedded MCU C8051F410. The device adopts high-speed 8051 μ C core, running at a maximum speed of 50 mi/s, minimizes power consumption and electromagnetic radiation, and improves the anti-interference ability of the system; A 12 bit a/D converter with built-in zero bit error rate, the sampling rate can reach 200 KS/s, and the maximum is 24 channel a/d conversion circuit input port, which simplifies the peripheral A/D conversion channel switching control circuit and realizes high-accuracy analog quantity sampling; In power saving mode, the typical current is less than 1 μ A. Working current at 32 kHz is only 16 μ A。 Based on the above characteristics, C8051F410 single chip microcomputer is used as the core of the system to simplify the design of signal sampling and sampling channel control circuit of the system and reduce the volume of the system. Use the circuit shown in Figure 2 to convert the voltage of 21 batteries. The LCD display circuit of the system adopts LCD low-power driver PCF8563 and I2C bus interface, which is simple and reliable

3 test data

in the voltage measurement experiment, ra=5 K Ω, rb=5 K Ω, LM324 is selected as the operational amplifier, and Agilent 34401 is selected as the comparison reference test equipment (the DC voltage test accuracy is 0.001 V). The battery pack composed of 10 batteries is tested. Table 1 shows the comparison of system test voltage, and figure 5 shows the measurement error. According to table 1 and figure 5, the measurement error of 12 V battery pack system is less than 0.1%

4 conclusion

through theoretical analysis and experimental verification, the battery monitoring system has advantages: (1) measuring a single battery of a battery pack with a low-cost ordinary optocoupler can meet the accuracy requirements of the system, save 90% of the device cost, and simplify the circuit design; (2) Due to the high isolation voltage of the optocoupler, the measurement range of the series battery voltage of the system can reach 2000 V, which is 3-5 times higher than the withstand voltage of the relay; (3) Using embedded C8051F410 single chip microcomputer, Nanyu allows direct input of up to 24 analog signals. The measuring circuit is simple and small

to sum up, the system realizes the stable and reliable application of ordinary optocoupler instead of linear optocoupler in terms of product supply, quality, transportation, storage, etc. as an international chemical giant, Johnson Matthey Yisi is not weak in accuracy, and realizes the use of low-cost circuits to solve the problem of high-precision and large-scale voltage measurement. The characteristics of small size, light weight and low cost make the system have a good application prospect in the application of portable pool group detection equipment to achieve electrical performance without meeting the requirements

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