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It can be possible, but the benefits outweigh the losses. If all the batteries are old, the driving range will not be extended much. Moreover, doubling the weight of the battery has a significant impact on the load of the electric vehicle itself. It is recommended to use one set before using the other set

1. It is possible to use batteries in parallel, but the battery you added must be charged separately, otherwise charging them together will result in a short lifespan.

2. Introduction to battery classification:

(1) Ordinary batteries; The electrode plate of a regular battery is composed of lead and lead oxide, and the electrolyte is an aqueous solution of sulfuric acid. Its main advantages are stable voltage and low price; The disadvantages are low specific energy (i.e. the energy stored per kilogram of battery), short service life, and frequent daily maintenance.

(2) Maintenance-free batteries: Due to their structural advantages, maintenance free batteries consume very little electrolyte and do not require distilled water supplementation during their service life. It also has the characteristics of shock resistance, high temperature resistance, small size, and small self discharge. The service life is generally twice that of a regular battery. There are also two types of maintenance free batteries on the market: the first type is to add electrolyte at the time of purchase and do not require maintenance during use (adding supplementary liquid); Another type is that the battery itself is already filled with electrolyte and sealed when it leaves the factory, so users cannot add any replenishment solution at all.

(3) Dry charged lead-acid battery: Its full name is dry charged lead-acid battery. Its main feature is that the negative electrode plate has a high storage capacity. In a completely dry state, it can store the obtained electricity for two years. When in use, only electrolyte needs to be added, and it can be used after 20-30 minutes.

3. When a battery is charged with direct current, the two poles generate lead and lead dioxide, respectively. After removing the power source, it returns to its pre discharge state and forms a chemical battery. Lead acid batteries are batteries that can be repeatedly charged and discharged, called secondary batteries. Its voltage is 2V, usually used by connecting three lead-acid batteries in series, with a voltage of 6V. The car uses 6 lead-acid batteries connected in series to form a 12V battery pack. Ordinary lead-acid batteries need to be supplemented with distilled water after a period of use to maintain the electrolyte containing 22-28% dilute sulfuric acid

A member of the China Electric Vehicle Alliance replied: If you want to add batteries for parallel use, it is possible, but the battery you added must be charged separately, otherwise charged together. The lifespan of the battery you added is very short. I have done this in the past, and charging the battery you added can easily cause the battery to explode. Please be careful, and if you want to add a battery, it is recommended to connect it in series. My phone is also connected, but I charge it separately. Serial connection means increasing voltage, but if you connect in parallel, although there is no significant increase in voltage, but you still replace a DC converter when adding batteries, it may easily damage the controller. This must be told that if the quality of the controller is good, it is easy to damage it if the quality is not good

Parallel charging of valve controlled sealed lead-acid batteries

Parallel connection of one battery only increases its capacity, just like two 10AH connected in parallel to 20AH, so it does not affect the motor and controller. Improper parallel connection of old and new batteries is not advisable, as it not only fails to achieve the expected effect but also damages good batteries

The capacity of the two batteries is similar, and they can be charged with a charger, but they need to be replaced with a high current one. A low current may overcharge the battery a bit

Two positive electrodes are disconnected using an air circuit breaker. Two charging ports, two charging devices separate for charging. After being fully charged, close the overhead switch and discharge in parallel. In theory, dual electric has a single electric range of X2. However, after parallel connection, the current decreases, so it should be able to run an additional 8-10 kilometers, right

The traditional charging method for 3 battery packs is to use series charging. The 36V and 48V valve regulated sealed lead-acid batteries currently used in electric vehicles are composed of 3 and 4 12V batteries connected in series. Previously, people were concerned that if batteries (or battery packs) were charged in parallel, there would be a bias effect due to the uneven voltage of the parallel batteries (or battery packs), and even some batteries would charge (discharge) another part of the batteries, which would exacerbate the unevenness of the parallel batteries (or battery packs). But our experimental results indicate that parallel charging will not encounter the above situation. On the contrary, parallel charging is beneficial for improving the uniformity of electric vehicle batteries (or battery packs). The following is an introduction to the test results we conducted in the central laboratory of Zhongshang Guotong Electronics Co., Ltd., for reference by interested personnel. The batteries used in the experiment were randomly selected from the production workshop of the company.

We will conduct parallel charging tests on 5 colloidal VRLA batteries that have been formed into 2V/200Ah batteries through series internalization in two groups. During the experiment, each battery's sub circuit was connected to an ammeter, and the current flowing through each sub circuit was measured as I1, I2, etc. There is also an ammeter connected to the main circuit to measure the total discharge current Io. The first group of two batteries are pre discharged with a constant current of 100A for 30 minutes (for battery 2) and 60 minutes (for battery 1) respectively, and then charged in parallel. The first step is to maintain a constant voltage of 2.4V and limit the current to 80A (total current). The second step is to maintain a constant voltage of 2.4V and charge directly until the current remains unchanged (see Figure 6-4). The second group of three batteries were pre discharged with a constant current of 100A for 30 minutes, 60 minutes, and 90 minutes respectively, and then charged in parallel. The charging method was the same as the first group of two batteries, with a total current of 100A (see Figure 6-5).

1. Current distribution during parallel charging process

From Figures 6-4, it can be seen that the charging current flowing through each battery is automatically adjusted according to the different states of charge of each electric vehicle battery. If the first battery has a higher amount of pre discharged electricity and less remaining capacity, its charging current will be higher. When it is charged for 73 minutes, the charging current reaches its maximum value of 50.9A, and then gradually decreases; The amount of electricity discharged in advance from battery number 2 is relatively low. If there is more remaining capacity, its charging current will be smaller, and it will gradually decrease after reaching the maximum value of 32.4A (charging for 30 minutes). As the charging process progresses, the difference in capacity between each battery becomes smaller, and the difference in charging current gradually decreases. When each battery is basically fully charged (charging for 5.5 hours), the charging current of each battery gradually tends to be consistent.

Figures 6-5 show the current distribution during the parallel charging process of three 2V/200Ah colloidal VRLA batteries. The result is basically the same as two batteries, with the only difference being that the charging currents of the three batteries are interrelated.

Figure 6-6 shows the parallel charging of two sets of 6DZM10 electric vehicle batteries. After each group of 3 batteries discharges 5A to 31.5V, the second group first uses a charger to charge for 4 hours, and then charges in parallel with the first group of batteries. It can be seen that the charging current of the two sets of batteries is also automatically allocated and adjusted according to their different states of charge before parallel charging. Its regularity is completely consistent with that of a 2V battery.

The test results in the above three scenarios indicate that the total charging current flowing through each battery (battery pack) is the same as the current value flowing through the bus. This means that during the parallel charging process of valve controlled sealed lead-acid batteries for electric vehicles, there will be no situation where one battery (battery pack) charges (discharges) another battery (battery pack). In the past, people regarded the inconsistent current flowing through each branch when charging batteries in parallel as a "forbidden zone" for battery maintenance work. Now it seems necessary to make corrections. Because it is this "bias current" effect that causes batteries with inconsistent states of charge to tend towards consistency. Now it is observed that MH/Ni batteries and lithium-ion batteries also have this pattern.

2. Voltage changes during parallel charging process

During the parallel charging process of two batteries, although their terminal voltage will continuously increase (as shown in Figures 6-7), they are always inconsistent until fully charged. The voltage difference (U2-U1) between the two batteries during the charging process is shown in Figures 6-8. Within 30 minutes of starting charging (U2-U1), the voltage remained almost constant at 20mV, and then quickly increased to the maximum value of 40mV. This is obviously related to the fact that the No. 2 battery has been charged until the voltage suddenly rises. However, due to the limitations of constant voltage charging and battery state of charge, the charging current of battery 2 began to decrease, resulting in a decrease in the total charging current, and u1 and U2 gradually approached. The charging voltage of the last two batteries is the same, and the total charging current is also the smallest. The slight difference in charging current of each battery at this time reflects that their self discharge speed is not completely the same.

Since the terminal voltages of the two batteries are different, why wouldn't there be a situation where one electric vehicle battery charges (discharges) the other battery during parallel charging? This is because the charging voltage U1 of the battery is always higher than its electromotive force E (or open circuit voltage) value, and the difference △ U1 (usually 60-70mV) is the internal resistance voltage drop of the battery. It is the product of the charging current I and the internal resistance r of the battery (including ohmic resistance, concentration polarization resistance, and electrochemical polarization resistance), that is, U1=E+△ U1; When the battery is in a discharge state, its terminal voltage U2 must be lower than its electromotive force (or open circuit voltage), and the difference △ U2 is the product of the discharge current and the internal resistance of the battery, that is, U2=E - △ U2. Under a 10 hour discharge rate, △ U2 is similar to △ U1. Therefore, when two batteries are charged in parallel, if one battery needs to charge the other battery, the terminal voltage difference between the two batteries must be greater than 2 △ U1, which requires a voltage of 100-150mV or more. The U2 to U1 values listed in Figure 6-8 are much smaller than 2 △ U1, so of course, there will not be a situation where battery 2 charges battery 1.

3. The impact of parallel charging on battery uniformity

The three 2V/200Ah colloidal sealed lead-acid batteries listed in Table 6-3 were both internalized and initially charged in series, and all subsequent charges were also charged in parallel. It can be seen that the initial discharge capacity of the three batteries is about 88% of the rated capacity, and there is a significant difference between them, with a relative range of 5.4% and a standard deviation σ It is 4.23. Afterwards, three parallel charging and series discharging were carried out. Not only has the battery capacity exceeded the rated value, but the difference between the batteries has also been further reduced: the relative range has been reduced from 5.4% to 1.5%, and the standard deviation σ It also decreased from 4.23 to 1.44.

After charging the aforementioned batteries in parallel and placing them at room temperature of 20-30 ℃ for 4 months, their discharge capacity has decreased, with relative range and standard deviation σ There has also been an increase. Continuing with parallel charging, the result not only restored the capacity of the electric vehicle battery, but also improved the uniformity between them.

Table 6-4 lists the changes in 5A discharge capacity of 6 6DZM10 electric vehicle batteries divided into 2 groups before and after parallel charging. The first group of batteries (1, 2, 3) had a shorter discharge time, which may be related to their insufficient charging. During parallel charging, this group of batteries charges more electricity than the other group, and their discharge time will be significantly prolonged; Although the discharge time of the second group of batteries (No. 4, 5, and 6) was relatively long, there were significant differences among the batteries. During the parallel charging process, the charging current of this group of batteries was relatively small, which is equivalent to uniform charging. Therefore, after parallel charging, although the discharge time increases very little, the difference between the three batteries is reduced. The reason why parallel charging can improve the uniformity of battery packs is because it utilizes the "bias current" phenomenon that occurs during parallel charging of batteries. Because the current flowing through each battery during the charging process is automatically adjusted based on the saturation level of the battery itself. At the beginning stage of charging, batteries that were previously undercharged will automatically be allocated a larger charging current, while batteries with a higher state of charge will automatically be allocated a smaller charging current. As the charging process progresses, the difference between them will gradually decrease, and finally, the charging states of each battery will tend to be consistent, with the same charging current, and the phenomenon of "bias current" will disappear.

It can be seen that whether it is a 2V single battery or a 12V or 36V battery pack, parallel charging is beneficial for improving their uniformity. Practical experience has proven that conducting small current parallel charging of electric vehicle batteries every month is effective in extending the service life of electric vehicle batteries. It should be pointed out here that each 6DZM10 battery is composed of 6 single batteries connected in series, so when charging 2 whole batteries in parallel, the 6 single batteries inside each battery are still connected in series. When there is a micro short circuit or severe water loss inside a single cell battery, which leads to a decrease in the performance of the entire battery, the effect of parallel charging on the uniformity between them is not very significant.

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