Design of automatic detection system for electric bicycle charger
charger is a key component in the power supply of electric bicycle. Unqualified charger will lead to overcharging, insufficient charging or unbalanced charging of battery, and directly affect its service efficiency (such as riding time after a charge) and service life. The charger has two main performance indicators: first, the charging process curve - the curve of the charging voltage and charging current changing with the charging time during the charging process. The chargers of different batteries have different optimal charging curves. The charging process is carried out according to this charging curve, so as to achieve the best effect of both filling the battery and protecting the battery. Qualified chargers should have a curve similar to the optimal charging curve; The second is specific energy, which is defined as the ratio of the charge and discharge of the standard battery by the new hydrogel charger that the research team is testing on a large scale. The standard value is between 1.05 and 1.10. If it is greater than this value, it indicates that there is overcharging during the charging process, while if it is less than this value, it indicates that there is insufficient charging. Manually record the measurement and draw the curve manually. The single test cycle is at least 9 ~ 10h, which not only costs a lot of manpower, but also human factors will greatly affect the specification, accuracy and reliability of the results, let alone further analysis of the experimental data. Since there is no special instrument for automatic detection of chargers, we use virtual similar 3 Experimental results instrument technology, based on PC and VB platform, the automatic detection system of electric bicycle charger is designed and developed. It can automatically detect the charging and discharging voltage, current, charge and discharge power and other parameters of 8 chargers at the same time, draw the charging process curve and conduct automatic or manual analysis. The battery voltage can be optionally 12V, 24V or 36V, It can be used for parameter debugging of charger development process and product quality sampling inspection of charger batch production process. Figure 1-1 is the block diagram of the detection system. In the dotted box, a, K, B, and K are the normally open contacts of the charging relay and the discharge relay respectively. The PC controls the charging relay to connect a and K through the relay control circuit, and successfully prints them on the ultimaker 2. The detected charger charges the battery and enters the charging measurement state: the PC obtains the terminal voltage and sampling voltage of the battery at both ends of the sampling resistance R through the data acquisition circuit, and the charging voltage = terminal voltage, Charging current = (sampling voltage terminal voltage)/R, charging amount = total charging time × Charging current (ah), and the charging end time is controlled by the preset charging end current; When the PC controls the K and B points of the discharge relay to be connected, and the battery discharges to the constant current electronic load, the terminal voltage and sampling voltage of the battery under the discharge state can be measured. The discharge voltage = terminal voltage, the discharge current = (terminal voltage sampling voltage)/R, and the discharged electricity = total discharge time × The discharge current (ah) and the discharge termination time are controlled by the preset discharge termination voltage. The system adopts standard battery. The detection process can be described as: discharge test → charge test → discharge test. The first discharge test is to provide the discharged standard battery; The charging test records the charging voltage and charging current during the charging process of the charger to the standard battery, and calculates the charged power; The second discharge test is to detect the discharged power of the battery after charging, which reflects the quality of the charged power. Compare the standard charging curve stored in advance with the charging process curve of the tested charger, combined with the measured specific energy value, evaluate the performance of the charger, and quickly judge whether the charger is qualified. When developing the smart charger with microcontroller, the program of the charger is adjusted according to the best charging curve of different batteries for different types of batteries, so as to develop a high-quality charger. 2 system hardware structure except PC, the hardware is mainly composed of charge and discharge control circuit, constant current discharge electronic negative to facilitate the next step of processing load, data acquisition card, etc
2.1 charge and discharge control circuit
each unit detection circuit is designed independently. In the dotted box of Figure 1-1, there is a unit circuit, which is composed of charge relay, discharge relay, sampling resistance R and sampling voltage attenuation resistance. The common terminals of the two charge and discharge relays in the circuit are connected in parallel and controlled by the output switching value in the data acquisition card. The sampling voltage attenuation resistance is to be compatible with the 0 ~ 10V range of the data acquisition circuit, The sampling resistance is 0.1 Ω/5W wire wound resistance. There are 8 such units in this system.
2.2 constant current discharge electronic load
in order to test the charging effect of the charger, the discharge test should be carried out on the charged standard battery. At present, the market mainly uses variable resistors, resistance discs, carbon rods, etc. as the discharge load, with low control accuracy and complicated work. A constant current discharge electronic load circuit developed by us for the automatic detection system is shown in Figure 2-1, and the use voltage is 6 ~ 42V, The discharge current is continuously adjustable in the range of 0 ~ 6a, and the constant current accuracy is 1%. In Figure 2-1, the discharge electronic load is composed of T1, T2, D1 and R6. The main power device T2 adopts the high-power Darlington tube mj10020, the reverse breakdown voltage BVCEO is 200V, the collector current ICM is 15a, the dissipation power PCM is 250W, and the magnification is 100; The push tube T1 uses a Darlington power tube TIP132, the reverse breakdown voltage BVCEO is 100V, the collector current ICM is 10a, the dissipation power PCM is 15W, and the magnification is 100; D1 is used for battery reverse connection protection, which is composed of C and B poles of TIP132, and R6 is the discharge resistance. In Figure 2-1, the constant current control circuit is composed of A1, R1, R2, R3, R4 and C1. A1 is the operational amplifier, TL062 is used, R2 is used for constant current setting, resistors R4 and R5 sample the change of discharge current, feed it back to A1, and automatically adjust the discharge current to the set value. The process is: when the discharge current I ↑→ VA, on the contrary, when I decreases, there is the opposite process. 150mm is added in the design × 50mm × 190mm radiator to cool the heat generated by T1 and T2 conduction power consumption. Choose a radiator with good surface flatness to avoid uneven stress during installation, and use heat-conducting silica gel. The circuit and the charge discharge control circuit form an independent unit with a unit size of 220mm × 150mm × 200mm, the system is installed by 8 units 940mm