In the lithium-ion
laptop battery management system, the need for a single
battery in the battery voltage detection. Application is now more direct sampling method, the method is not only complex, in the practical application of the battery pack will also affect the consistency. Many factors, however, can not ignore the impact of the circuit. The author of this article through a practical voltage detection circuit, the circuit analysis of the performance of
batteries using the
Inspiron 1100 battery model analysis of the impact of the causes and put forward to reduce the impact.
In the sony battery voltage measurement system is difficult: how to detect the series in every single battery voltage of the batteries, which are to be compared with the common voltage reference, so as to facilitate the sampling voltage signal. The safety of lithium-ion battery voltage in general 2.7 ~ 4.2V, so the reference voltage of 5V of the A / D converter, single-voltage battery is in this. If the reference is not systematic, then only the first n the battery voltage will be the only pre-n and the battery voltage, which has exceeded the A / D conversion reference voltage range, the voltage through the measurement into the system compared with the same reference Is essential to.
Experiments using the same 10 lithium-ion battery, rated capacity of 3Ah, batteries used in series structure of the battery pack through the cycle of experiments conducted to test the dynamic process of lithium-ion battery pack. In the experimental battery pack before the first single cells on the 3rd cycle, so that the capacity and stability. The battery charge and discharge system: 0.50C constant current charge to 42V, and then charging voltage to 42V to reduce the current 0.05C up; battery discharge current 0.50C to 30V. In the course of the experiment, the single battery protection: protection of the charge-off 4.35V, over-discharge protection of 2.50V.
The author of this article for the design of a practical battery voltage measurement circuits, as shown in Figure 1, which is composed of subtraction op amp circuits, each battery voltage Vn ‘corresponds to a subtraction circuit. Vn + for only the first n positive relative to the land of the battery voltage, Vn-for the first n only relative to the negative battery voltage of the earth.
10 because of lithium-ion battery pack maximum voltage of about 42V, for the operational amplifier, more than the maximum voltage, the subtraction in the circuit used in voltage attenuation, and then proceed to enlarge. As part of the enlarged use of the same magnification, it can be simulated on the switch, so the whole detection circuit only need one amplifier can be cost-effective.
In actual use, 10 times in order to ensure the accuracy of voltage attenuation, the use of R resistance 33kΩ (1% accuracy). Because of the large high-precision resistors made special needs, but also expensive. In the experimental battery pack in the performance of a marked decline, shown in Figure 2. 52 times the previous cycle (0.5C charge and discharge), the Asus battery pack, single battery voltage discharge cut-off that there are great differences, with the cycle, the order they were asked, “lining up” phenomenon more obvious, but also in the first About 30 cycles, battery discharge yet to 30V, the first of a battery voltage discharge has been in a state of protection, resulting in the termination of the discharge of the battery, battery pack all of a sudden reduction in capacity. In order to verify the online testing is caused by leakage current, 52 cycles, the battery pack in a first and 10 for the battery exchange, the continued cycle of experiments and found that: 10 of the battery discharge termination A slight drop in voltage, and a section of the termination of the discharge voltage has been greatly improved; due to the original article is no longer in a battery discharge over the protection of state, the No. 2 battery which had a discharge protection. Experiment over: the voltage detection circuit to a certain extent there is leakage, which were measured,
In the charging process, the circuit of the charge current detection through each line voltage detection circuit to be part of the current points out that the closer the negative battery cell, the more diversion, so that the charging process, the more Close to the battery cathode battery charge current greater. Discharge process is the same, the more close to the battery anode, the smaller the battery discharge current. Throughout the cycle, close to the cathode of the battery cell, in charge of electricity, out of less electricity; and close to the negative battery into the battery power of a small, and the release of more electricity, which is caused by the 8027U battery pack inconsistency . With the cycle, exacerbated by inconsistency, even if the battery’s initial state, as a result of the cumulative effect exists, so that the battery pack in the course of the cycle as a result of leakage and inconsistent, although relatively small leakage, but the Dorgan-ray detection As well as the cumulative long-term, it will affect the consistency of the F2299A battery pack.
In order to reduce leakage current, increased test taking input impedance, or resistance to R into 200kΩ (1% accuracy), because the resistance of resistance deviation greater precision, experimental results show that: current leakage significantly reduced. Will be revised voltage detection circuit, in accordance with the above-mentioned experimental battery system to do the experimental cycle. The results compared with Figure 2, voltage detection circuit to the battery pack in the single battery voltage discharge termination of the impact has been a lot of small, but the battery pack in the single battery voltage discharge or terminate the order they will be “lining up” phenomenon .