Can electric car batteries be used in parallel?

  It can be, but it is not worth the loss. If it is an old battery, it will not increase the mileage. Besides, the weight of the battery is doubled. It has a great impact on the load of the electric vehicle. It is recommended to use another group in another group.

　1. It is OK to use the battery in parallel, but the battery you add must be charged separately, otherwise it will be charged together, and the battery life you add is very short.

　2. Introduction to battery classification:

　(1) Ordinary battery; the plate of an ordinary battery is composed of an oxide of lead and lead, and the electrolyte is an aqueous solution of sulfuric acid. Its main advantage is that the voltage is stable and the price is cheap; the disadvantage is that the specific energy is low (that is, the energy stored per kilogram of battery), the service life is short, and the daily maintenance is frequent.

　(2) Maintenance-free battery: Maintenance-free battery due to its own structural advantages, the consumption of electrolyte is very small, and it is basically unnecessary to supplement distilled water during the 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 normal battery. There are two types of maintenance-free batteries on the market: the first one requires no maintenance (addition of replenishing liquid) during the one-time application of the electrolyte at the time of purchase; the other is that the battery itself has been charged with electrolyte and sealed off at the factory. The user can't add supplemental liquid at all.

　(3) Dry-charged battery: Its full name is dry-charged lead-acid battery. Its main feature is that the negative plate has high storage capacity. In the completely dry state, it can save the obtained electricity within two years. When using, just add the electrolyte and wait for 20-30 minutes.

　3. When the battery is charged by DC, the two poles respectively produce lead and lead dioxide. After removing the power supply, it returns to the state before discharge to form a chemical battery. A lead storage battery is a battery that can be repeatedly charged and discharged, and is called a secondary battery. Its voltage is 2V, usually three series of lead batteries are used in series, the voltage is 6V. The car uses six lead batteries connected in series to a 12V power pack. Ordinary lead storage batteries should be supplemented with distilled water after a period of use to keep the electrolyte containing 22-28% of dilute sulfuric acid.

　Members of the China Electric Vehicle Alliance replied: You want to add batteries in parallel, it is OK, but the battery you add must be charged separately, or you can charge it together. The battery life you added is very short. I have done this before, and added That battery charging is very easy to charge the battery, pay attention to it, if you want to add batteries, it is recommended to connect in series. My current is also connected, but I am charging separately. Serial connection is to increase the voltage, but if you do not increase the voltage in parallel, but you still need to replace a DC converter when adding the battery, but it may damage the controller. This must tell you that if the quality is better, If the quality is not good, it is very easy to break.

　Parallel charging of valve-regulated sealed lead-acid batteries

　1 battery parallel connection only increases its capacity, like 20AH in parallel with two 10AH, so it has no effect on the motor and controller. Old and new, improper parallel connection of good or bad battery is not desirable, not only cannot get the expected effect will damage Good battery.

　2 battery capacity is similar, you can use a charger to charge, but to be replaced by a large current, a small current is a bit overcharged

　The two positive poles are disconnected by air. Two electric outlets, two impulses are separately charged. After flushing, close the air and open the parallel discharge. In theory, the double power is the mileage of single power X2. But after the parallel connection, the current becomes smaller, and it should be able to run out for 8~10 kilometers.

　3 battery packs traditional charging methods are connected in series. The 36V and 48V valve-regulated sealed lead-acid batteries used in electric vehicles are made up of 3 and 4 12V batteries in series. In the past, people were worried that if the battery (or battery pack) was charged in parallel, the bias current would be caused by the uneven voltage of the parallel battery (or battery pack), and even if some of the batteries were charged (discharged) to another battery. This leads to increased non-uniformity of the parallel battery (or battery pack). However, our test results show that the above situation does not occur in parallel charging. Conversely, parallel charging is advantageous for improving the uniformity of the electric vehicle battery (or battery pack). The following is the test results of our test in the central laboratory of China Merchants Guotong Electronics Co., Ltd., for the reference of interested personnel. The batteries used for the test were randomly selected from the company's production workshop.

　We conducted a parallel charging test in which two 5V/200Ah colloidal VRLA batteries were serialized into a completed 2V/200Ah. During the test, each sub-circuit of the battery is connected with an ammeter, and the currents flowing through the respective branches are I1, I2, etc., respectively. An ammeter is also connected to the total circuit to measure the total discharge current Io. The first group of 2 batteries were previously discharged with a constant current of 100 A for 30 min (No. 2 battery) and 60 min (No. 1 battery), and then charged in parallel. The first step is constant voltage 2.4V current limit 80A (total current), the second step is to maintain a constant voltage of 2.4V, straight charge until the current is unchanged (see Figure 6-4). The second group of 3 batteries were previously discharged with 100A constant current for 30min, 60min and 90min respectively, and then charged in parallel. The charging method was the same as that of the first group of 2 batteries, and the total current was 100A (more Figure 6-5).

　1. Current distribution during parallel charging

　As can be seen from Fig. 6-4, the charging current flowing through each battery is automatically adjusted according to the state of charge of each electric vehicle battery. No. 1 battery pre-discharges more power, and the remaining capacity is less, then its charging current is larger. When charging to 73min, the charging current reaches the maximum value of 50.9A, and then gradually decreases; less. If the remaining capacity is large, then its charging current is small, and the charging current reaches a maximum value of 32.4A (charging for 30 minutes) and then gradually decreases. Thereafter, as the charging process progresses, the difference in capacity of each battery is small, and the difference in charging current is gradually reduced. When each battery is substantially fully charged (charging for 5.5h), the charging current of each battery gradually becomes uniform.

　Figure 6-5 shows the current distribution during the parallel charging of three 2V/200Ah colloidal VRLA cells. The result is basically the same as the two batteries, the only difference is that the charging currents of the three batteries are interlaced.

　Figure 6-6 shows the parallel charging of two groups of 6DZM10 electric vehicle batteries. After 5 batteries of each group are discharged to 31.5V, the second group is charged with the vehicle charger for 4 hours, and then charged in parallel with the first group of batteries. It can be seen that the charging currents of the two groups of batteries are also automatically assigned and adjusted according to their different state of charge before parallel charging. Its regularity is exactly the same as the 2V battery.

　The test results in the above three cases show that the sum of the charging current flowing through each battery (battery pack) is the same as the current flowing through the bus line. This means that a battery (battery pack) does not charge (discharge) another battery (battery pack) during parallel charging of a valve-regulated sealed lead-acid battery for an electric vehicle. In the past, the inconsistency of the current flowing through each branch when the batteries were connected in parallel was regarded as the "forbidden zone" for the battery maintenance work, and it seems necessary to correct it now. Because it is this "bias flow" effect that makes the original cells with inconsistent state of charge tend to be consistent. It is now observed that MH/Ni batteries and lithium ion batteries also have this rule.

　　2. Voltage variation during parallel charging

　During the parallel charging process of two batteries, although their terminal voltages will increase continuously (as shown in Figure 6-7), they are always inconsistent before they are fully charged. The voltage difference between the two batteries during charging (U2) The change of -U1) is shown in Figure 6-8. Within 30 minutes of starting charging (U2-U1), it remained almost unchanged at 20 mV, and then quickly increased to a maximum of 40 mV. This is obviously related to the fact that the No. 2 battery has been charged to a voltage surge. However, due to the constant voltage charging and the state of charge of the battery, the charging current of the No. 2 battery begins to decrease, resulting in a decrease in the total charging current, and u1 and U2 are gradually approaching. The last two batteries have the same charging voltage and the lowest total charging current. At this time, the slight difference in charging current of each battery reflects that their self-discharge rates are not exactly the same.

　Since the terminal voltages of the two batteries are different, why does the electric battery of one electric vehicle not charge (discharge) the other battery during the parallel charging process? This is because the charging voltage U1 of the battery is always higher than its electromotive force E (or open circuit voltage). The difference ΔU1 (usually 60~70mV) is the internal resistance drop of the battery. It is the charging current I and the battery. The internal resistance r (including the Ohmic internal resistance, the concentration polarization internal resistance and the electrochemical polarization internal resistance), that is, U1=E+△U1; when the battery is in the discharge state, its terminal voltage U2 is necessarily lower than its electromotive force ( Or open circuit voltage), the difference ΔU2 is the product of the discharge current and the internal resistance of the battery, that is, U2=E-△U2. In the case of a 10h rate discharge, ΔU2 is close to ΔU1. Therefore, when two batteries are charged in parallel, if one battery is to be charged to another battery, the terminal voltage difference between the two batteries must be greater than 2 ΔU1, that is, 100 to 150 mV or more is required. The U2~U1 values listed in Figure 6-8 are much smaller than 2△U1. Of course, there is no case where the No. 2 battery charges the No. 1 battery.

　3. Effect of parallel charging on battery uniformity

　The three 2V/200Ah colloid-sealed lead-acid batteries listed in Table 6-3 are charged in series for internalization and first charge, and are charged in parallel for each subsequent charge. It can be seen that the initial discharge capacity of the three batteries is about 88% of the rated capacity, and the difference between them is large, the relative range is 5.4%, and the standard deviation σ is 4.23. Thereafter, three parallel charging and series discharging were performed. Not only the battery capacity has exceeded the rated value, but also the difference between the batteries is further reduced: the relative range is reduced from 5.4% to 1.5%, and the standard deviation σ is also reduced from 4.23 to 1.44.

　After the above batteries are charged in parallel, they are allowed to stand for 4 months at room temperature of 20 to 30 ° C, and the discharge capacity thereof is decreased, and the relative range and standard deviation σ are also increased. Then parallel charging is performed, and as a result, not only the electric vehicle battery capacity is recovered, but also the uniformity between them is improved.

　Table 6-4 lists the changes in the 5A discharge capacity of the six 6DZM10 electric vehicle batteries divided into two groups before and after parallel charging. The first group of batteries (1, 2, 3) had a short discharge time, which may be related to their original insufficient charging. In the parallel charging process, this group of batteries is charged more than the other group, and its discharge is more. The time will be significantly longer; the second group of batteries (4, 5, 6), although the original discharge time is longer, but the difference between the batteries is large, the battery charging current is small during the parallel charging process, equivalent to Equal charge. Therefore, after parallel charging, although the discharge time is increased little, the difference between the three batteries is reduced. The reason why the parallel charging can improve the uniformity of the battery pack is to utilize the phenomenon of "bias current" which occurs when the battery is connected in parallel. Because the current flows through each battery during charging is automatically adjusted according to the degree of charge saturation of the battery itself. At the beginning of charging, the battery that was originally undercharged will be automatically assigned a larger charging current. The battery with the higher state of charge will be automatically assigned to a smaller charging current. As the charging process progresses, the difference between them will be Gradually reduce, and finally the state of charge of each battery tends to be the same, the charging current is the same, and the "biased" phenomenon disappears.

　It can be seen that whether it is a 2V single cell or a 12V or 36V battery pack, parallel charging is beneficial to improve their uniformity. Practical experience has shown that a small current parallel charging of electric vehicle batteries every one month is very effective for extending the service life of electric vehicle batteries. It should be noted here that each 6DZM10 battery is made up of 6 single cells connected in series, so when two integrated batteries are connected in parallel, the 6 single cells inside each battery are still charged in series. When a micro-short circuit or severe water loss inside a single cell causes the performance of the entire cell to drop, the effect of parallel charging on the uniformity between them is less significant.

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　Prevention of valve-regulated sealed lead-acid battery vulcanization method Valve-controlled sealed lead-acid battery thermal runaway failure analysis Valve-controlled sealed lead-acid battery thermal runaway reason Valve-controlled sealed lead-acid battery plate typical failure analysis valve-controlled sealed lead Relationship between acid battery life and temperature Valve-regulated sealed lead-acid battery charging speciality Valve-regulated sealed lead-acid battery in the process of polarization charging valve-controlled sealed lead-acid battery in the rapid charging process Valve-controlled seal for electric vehicles Lead-acid battery open circuit voltage provides on-line diagnostic technology for valve-controlled sealed lead-acid battery state of charge

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