Electric car often has the fault two: motor spinning when stopped (battery vulcanization):
1. The battery voltage in the state of under-voltage critical will appear when turning and stopping,
2. Poor contact with the battery connector will also occur this fault,
3. The speed control turns the line to break the state and the brake power off switch is faulty.
The main cause of battery vulcanization is that a layer of white and hard crystals are attached to the surface of the negative plate inside the battery. After charging, it is still unable to peel off the surface of the negative plate and convert the lead sulphate into active substance. This is Sulphur, Acidification, abbreviated as “vulcanization”. The vulcanized battery is like a film on the negative plate cover, causing the negative plate reaction to be greatly reduced, resulting in battery failure. In this Article we will talk about the softening of the battery cathode plate.
Battery Cathode Plate Softening
Intuitive inspection: During the charging process, the electrolyte is extracted. If the electrolyte is found to be red or black, or even dark into mud, it means that the battery cathode plate has softened. In terms of appearance, the surface of the cathode plate gradually becomes soft from the solid at the beginning until it becomes paste. At this time, due to the decrease in the surface area of the cathode plate, it will lead to a decrease in battery capacity. Although there are different theoretical explanations for the softening of the battery cathode plate, it can be observed that the structure of the active substance of the cathode plate is changing during the use of the battery under the microscope. There are fewer and fewer micropores, and finally a coral structure is formed. This process is definitely going to hap‐ pen. It is only related to the cycle process and discharge depth. The softening and shedding of active substances on the cathode grid can be said to be inevitable. With the progress of the discharge cycle, the surface of the active substance shrinks and forms a core into a coral structure. Multiple discharge cycles increase the accumulation of pores, increasing the pores, destroying the positive structure, and causing the softening and falling off of the active substance.
Causes of Battery Cathode Plate Softening Failure
Because the positive plate active substance lead dioxide itself is not firmly bonded, lead sulphate is formed during discharge and returned to lead dioxide when charging. The molar volume of lead sulphate is larger than that of lead sulphate, so the volume of the active substance expands during dis‐ charge. If 1 mole lead dioxide is converted into 1 mole lead sulphate, the volume will increase by 95%. In this way, the repeated contraction and expansion make the bond between lead dioxide particles gradually relaxed and easy to fall off. If only 20% of the 1 mole of lead dioxide active substance is discharged, the degree of contraction and expansion will be greatly reduced, and the bond damage becomes slower. Therefore, the deeper the discharge depth, the shorter the cycle life.
The reasons for the softening of the cathode plate are as follows.
The first reason is that high current discharge: especially when carrying people, carrying goods, going uphill and starting up, the battery discharge current can reach dozens of amperes. Lead oxide on the surface of the battery cathode plate participates in the reaction quickly. The local sulfuric acid formed after the deep lead oxide reaction has been converted into water. There is a lack of sulfuric acid to participate in the reaction, and the Sulphur in the partition. Acid diffusion first reaches the surface, so the alpha oxygen lead on the surface is forced to participate in the reaction. After charging, it forms beta lead oxide, which cannot be reduced to alpha lead oxide. The branches become leaves, and the positive plate softens. Electric motorcycles work in high current discharge for a long time, so most of them will be softened by the positive plate.
The second reason is over discharge: such as the frequent use of undervoltage protection to reverse electricity. The beta lead oxide on the surface of the cathode plate is no longer enough, so alpha lead oxide also has to participate in the reaction, causing the branch to turn into leaves, causing the cathode plate to soften, and the cathode plate soften, which will block the leaves of the branches to block the sunlight. That is to say, the falling lead oxide in the terminology will block the through hole and form a semi through. Holes and closed holes, blocking the channels of sulfuric acid pre‐ vent the blocked lead oxide from participating in the reaction, and the capacity of the battery will also be significantly reduced.
The third reason is the precipitation of the battery cathode plate: Due to the charger, the floating charging pressure is too high, resulting in the battery being overcharged for a long time. During the charging process, a large amount of gas overflows in the pore of the plate, causing pressure in the pole hole. Under the high voltage “brush”, the active substance falls off and forms a positive plate to soften. Therefore, a large amount of gas precipitation will not only cause water loss. And it is also a condition for the formation of some positive plate softening. After some batteries lose water, the reaction area of the positive plate decreases, and the corresponding part of the positive plate cannot function. The current will be concentrated in other parts that do not lose water and vulcanize, resulting in the local softening of the positive plate. The current density of the positive plate per unit area increases, which is similar to the failure mechanism of high current discharge; vulcanization will reduce the real reflection area of the negative plate. Therefore, dewater loss and vulcanization are also an important reason for the early softening of the positive plate.
The fourth reason is high current charging: This will also cause the softening of the positive plate. Using chargers with large output current to charge small-capacity batteries, such as charging 10AH batteries with 20AH chargers, will heat the battery and increase the temperature of electrolyte, thus making the active substances expand, soft and easy to fall off.
In this Article, according to the fault happens in different position, establish vehicle fault table, analyze the consequences of failure may cause and the causes of failure. Combined with hardware limitations, and the maximum guarantee system performance requirements, passive software redundancy fault-tolerant strategy is put forward, give an example to analysis the pros and cons of this method.
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