The whole process of DIY making large-capacity lithium battery for NIU N1S electric vehicle
Verfasst: Mo 27. Jun 2022, 09:18
The DIY lithium battery has been used for 2 years before, and it feels that the capacity has not deteriorated. It can run more than 100 kilometers with the original battery. Recently, the idea of making another set of batteries with a larger capacity suddenly emerged, and I specially recorded the whole production process, so everyone can take a look.
Battery assembly process
Before DIY assembly, it is necessary to select the battery. Lithium batteries are in deep water. At present, you can't buy excellent lithium battery cells on the market. What you can buy are generally defective products or dismantled products eliminated by manufacturers, and the finished batteries are even more pitted. The craftsmanship is not clear at all, so I have to do it myself. I won't touch the soft pack battery. I originally planned to buy the recently popular 32650 lithium iron phosphate battery cell, which is said to be brand new and unused, with a capacity of about 5.5AH, and the price is only 7 yuan per piece. To form a 60V 22AH lithium battery, only 4 batteries are needed in parallel and then 20 series are connected in series. A total of 80 batteries only cost 560 yuan, and the protection board and accessories are cheaper than 20AH lead-acid batteries. However, although the lithium iron phosphate battery has a long life and high safety, it has a disadvantage that the energy density is too low, and the original battery can only be made 22AH. If you use 18650 cells, the original battery size can be 170 cells (if you use 18650 self-driving), that is, 10 parallel 17 series, the current cost-effective domestic cells are only about 2.5AH, about 8 yuan per section, that is to say Can only do 25AH.
After looking around, I decided to buy Lishen 55AH large single ternary battery. This battery is brand new and unused (there will be connection marks after use, even if it is polished), the capacity is 55AH, and the weight of a single cell is 1.15KG. It's really not easy to buy a good battery. You can't find it when you look for the battery. You have to find a reliable business first. Another reason for choosing this battery is that its size is 2 long, 148mm high, 132mm thick and 27mm thick. , the height is only 132mm, and the upright placement is similar to that of the Mavericks battery.
The battery cell is made of aluminum, the positive and negative electrodes are also made of aluminum, and there is an explosion-proof valve in the middle. In the event of a short circuit and high temperature, the explosion-proof valve will be opened to release the pressure to ensure safety. Aluminum electrodes are not easy to weld, and merchants have spot-welded nickel strips to facilitate welding. The appearance of the cells is very flat, and there is no bulging phenomenon. Since this kind of battery is said to be brand new, it is a defective product eliminated by the manufacturer. Although it is a defective product, the price is very cheap, and it is not unusable. For example, when a manufacturer makes a lithium battery pack, the internal resistance needs to be matched, and those with large differences in internal resistance will be eliminated and circulated on the market.
Because the battery pack is connected in series, the voltage, capacity, and internal resistance of the cells must be kept the same. When purchasing, the merchant is entrusted to perform over-capacity matching. The merchant labels the capacity test results on the cells. I use the internal resistance test. The overvoltage measured by the instrument is very consistent around 3.4V, and the internal resistance is also around 0.8mΩ. Although I bought a 55AH battery, the merchant's actual measured capacity has 16 57AH batteries, and only one is 56AH. This 56AH battery will become a short board. When buying batteries, it should also be noted that some merchants will refurbish the batteries whose capacity has been seriously reduced after dismantling. The core has little practical value.
The detection is correct, let's get started. First put a piece of 3M EVA high temperature double-sided tape on the top and bottom of the cell, and leave the middle empty for easy heat dissipation (in fact, the Mavericks N1s only has a maximum current of 30A, so it will not generate heat at all).
The use of double-sided tape is also conducive to assembly, so that the cells are tightly attached together, but only high-temperature-resistant double-sided tape can be used, not ordinary foam double-sided tape.
On the side of the rechargeable battery, you can see that there is a 3mm gap between the cells and the cells. This kind of large single cell may bulge after a period of use, which also leaves a certain space for the bulge. The outer skin of the battery is pasted by the merchant, and some colors are different.
Later, I thought that only the outer skin is isolated between the battery core and the battery core, just in case an isolation material has to be added, such as epoxy board or highland barley paper. I bought less epoxy board, just add highland barley paper to each cell. Highland barley paper can also be insulated and resistant to high temperatures.
Paste the highland barley paper and then paste the double-sided tape. This process is very simple and does not take much time. The cells are to be used in series. You can use the positive and negative electrodes to be arranged alternately, and the positive and negative electrodes can also be arranged side by side, but the series line can only be crossed, so the series line will be longer and the internal resistance will be larger, so it is generally recommended. Use a cross arrangement. As mentioned earlier, there is a cell with a capacity of only 26AH. Put it on the sixth sheet. If it is placed on the first sheet, it will decay faster.
The cells are composed of two groups, one group is 9 pieces, and the other group is 8 pieces, for a total of 17 pieces. Use 5CM wide fiberglass tape to fix each group of cells. This fiberglass tape is very sticky and tough, and is very suitable for fixing batteries.
After wrapping two circles of tape, there is not much heat dissipation gap left, but this battery 1C will not heat up when placed, so there is no need to consider this problem.
The bottom of the cell should be in contact with the battery box, and a piece of highland barley paper or epoxy board should also be attached as a whole, and then attached with glass fiber tape, and the corners should be glued around to prevent wear.
An epoxy board is used to isolate the two sets of batteries. Double-sided tape and highland barley paper are not used here. Because the whole set is quite heavy, if the batteries are placed vertically in the future, the tape in the middle will be flattened.
Then fix the two sets of batteries together with fiberglass tape. There are 17 strings of cells, and there is an empty one on one side. If the Mavericks exceeded the voltage, it would prompt an error, so I would have directly assembled 18 strings. The left side is now empty. I didn't have anything else on hand, so I sawed a few pieces of wood and plugged it.
Then there is the welding part. At the beginning, I was going to use red copper sheets to connect. I used 1mm thick red copper sheets here. The internal resistance of red copper sheets is low, which is more suitable for connecting materials. The copper skin is thick, so I had to cut it casually with scissors.
It is easier to eat tin by making a gap in the copper sheet, but there is nothing to stabilize the copper sheet, so it is impossible to make a half hole, so I have to make a round hole on the side and then cut it open.
Cut the gap with scissors, and level the copper sheet to facilitate tinning. I don't care if it doesn't look good, anyway, I can't see it after it's soldered. Apply a layer of solder to the copper connection end to facilitate soldering. Then use a utility knife to randomly scratch the electrode nickel sheet, which makes it easier to eat tin, and use a cotton swab to apply a layer of flux.
Apply a layer of tin to the nickel sheet of each electrode first. When tinning, I covered the electrodes around the electrodes to prevent short circuits caused by misoperation or falling tin beads (there is only a distance of about 3mm between the electrodes and the shell). Note that a 200W soldering iron is used here, and the temperature is as high as 400°. The time on the electrode is as short as possible, no more than 1 second. Immediately after the soldering iron is removed, cover the electrode with a wet towel to prevent the high temperature from being instantly transferred to the inside of the battery and damage the chemical substances inside the battery.
The same is true during formal welding, block other places to prevent misoperation, pay attention to the temperature... It is best to weld the series strip between the two sets of batteries last, otherwise it may cause electric shock.
After soldering, because it cannot be soldered for a long time, the copper sheet only has to be pulled for one second after being pressed, and the solder joints are not good-looking like a cat gnawed. I also tried welding with a nickel piece and a copper piece. Even if the nickel piece is pulled off, the solder joint will not come off and it is very stable. It can be said that the biggest difficulty of DIY this battery is welding. Friends who are not good at welders should buy the kind that screw directly!
Once the battery is connected, the next step is to install the protective plate. Lithium batteries cannot be overcharged and overdischarged. Once overdischarged, the battery will be scrapped. Overcharging may cause accidents such as fire, so the protection board is essential. I bought the Yanyang BMS protection board here. The price is relatively expensive. I bought it mainly because it can be directly connected without cracking the protocol. All communications are isolated. The current I bought is the smallest 70A, which is enough.
Solder the protection board cable and power on the protection board for testing. Before energizing the protection board, check whether the connection is correct. Use a multimeter to measure one by one from the cable B-. The voltage is increased by 3.4V, indicating that there is no problem with the connection. The temperature sensor cable is covered with an asbestos tube in the middle. The temperature sensor cable is very thin. After aging, it may fall on the battery and burn the protective plate, so it must be covered.
After installing the protection board APP, turn on the power switch of the protection board and connect the protection board smoothly. The Yanyang protection board APP interface is relatively simple.
But you need to enter the parameter settings to set the parameters first. I set the battery type, capacity and number of strings. The parameters should be set according to the actual situation of the cell, and other parameters can be defaulted.
After the setting is completed, it can be seen in the real-time status that the protection board is working normally, the temperature sensor is normal, and the voltage of the cell is very consistent. The error is only 0.006V, which can be ignored.
Finally, 6 epoxy boards were sawed to wrap the battery, because the battery is to be placed in a stainless steel shell. The epoxy board has the characteristics of isolating high temperature, flame retardant and insulating, so it is very good for wrapping the battery.
After the modification is completed, the voltage of the cell is only 3.4V, which is almost no electricity. Please charge it first. What I use here is a modified Delta power supply for charging, the voltage can be adjusted from 1-120V, and the charging current can also support up to 12A. Lithium batteries are generally recommended to be charged at 0.2C, which means that this 55AH battery is best charged with a current of no more than 11A. The charging time is the capacity/current, but the current will become very small in the final stage, so generally an extra hour is added. It takes 6 hours to charge with 10A current, and 8 hours to charge with 8A current.
Ready to test mileage the next day. I ran 116KM under the condition of an adult, and there are a lot of climbing roads... After running 116km, there is still 21% of the battery left.
I continued to run the next day. After running for another 35KM, I finally ran out of electricity. I set the protection below 3V. I looked at the picture and it happened to be the battery with a capacity of only 26AH before, that is, the 6th string was put first. Out of power. The discharge capacity recorded by the protection board is 59AH, which is 3AH higher than the actual capacity of 56AH. It should be the credit of the E-ABS power recovery. The new 55AH battery and the original 20AH battery can run 200KM at a time without any problems.
Think about the original large lithium pack of Mavericks, the capacity is only 35AH, mine is 55AH, and the cost of making it is less than half of the large lithium pack... It seems that the battery made by myself is still very cost-effective.
Battery assembly process
Before DIY assembly, it is necessary to select the battery. Lithium batteries are in deep water. At present, you can't buy excellent lithium battery cells on the market. What you can buy are generally defective products or dismantled products eliminated by manufacturers, and the finished batteries are even more pitted. The craftsmanship is not clear at all, so I have to do it myself. I won't touch the soft pack battery. I originally planned to buy the recently popular 32650 lithium iron phosphate battery cell, which is said to be brand new and unused, with a capacity of about 5.5AH, and the price is only 7 yuan per piece. To form a 60V 22AH lithium battery, only 4 batteries are needed in parallel and then 20 series are connected in series. A total of 80 batteries only cost 560 yuan, and the protection board and accessories are cheaper than 20AH lead-acid batteries. However, although the lithium iron phosphate battery has a long life and high safety, it has a disadvantage that the energy density is too low, and the original battery can only be made 22AH. If you use 18650 cells, the original battery size can be 170 cells (if you use 18650 self-driving), that is, 10 parallel 17 series, the current cost-effective domestic cells are only about 2.5AH, about 8 yuan per section, that is to say Can only do 25AH.
After looking around, I decided to buy Lishen 55AH large single ternary battery. This battery is brand new and unused (there will be connection marks after use, even if it is polished), the capacity is 55AH, and the weight of a single cell is 1.15KG. It's really not easy to buy a good battery. You can't find it when you look for the battery. You have to find a reliable business first. Another reason for choosing this battery is that its size is 2 long, 148mm high, 132mm thick and 27mm thick. , the height is only 132mm, and the upright placement is similar to that of the Mavericks battery.
The battery cell is made of aluminum, the positive and negative electrodes are also made of aluminum, and there is an explosion-proof valve in the middle. In the event of a short circuit and high temperature, the explosion-proof valve will be opened to release the pressure to ensure safety. Aluminum electrodes are not easy to weld, and merchants have spot-welded nickel strips to facilitate welding. The appearance of the cells is very flat, and there is no bulging phenomenon. Since this kind of battery is said to be brand new, it is a defective product eliminated by the manufacturer. Although it is a defective product, the price is very cheap, and it is not unusable. For example, when a manufacturer makes a lithium battery pack, the internal resistance needs to be matched, and those with large differences in internal resistance will be eliminated and circulated on the market.
Because the battery pack is connected in series, the voltage, capacity, and internal resistance of the cells must be kept the same. When purchasing, the merchant is entrusted to perform over-capacity matching. The merchant labels the capacity test results on the cells. I use the internal resistance test. The overvoltage measured by the instrument is very consistent around 3.4V, and the internal resistance is also around 0.8mΩ. Although I bought a 55AH battery, the merchant's actual measured capacity has 16 57AH batteries, and only one is 56AH. This 56AH battery will become a short board. When buying batteries, it should also be noted that some merchants will refurbish the batteries whose capacity has been seriously reduced after dismantling. The core has little practical value.
The detection is correct, let's get started. First put a piece of 3M EVA high temperature double-sided tape on the top and bottom of the cell, and leave the middle empty for easy heat dissipation (in fact, the Mavericks N1s only has a maximum current of 30A, so it will not generate heat at all).
The use of double-sided tape is also conducive to assembly, so that the cells are tightly attached together, but only high-temperature-resistant double-sided tape can be used, not ordinary foam double-sided tape.
On the side of the rechargeable battery, you can see that there is a 3mm gap between the cells and the cells. This kind of large single cell may bulge after a period of use, which also leaves a certain space for the bulge. The outer skin of the battery is pasted by the merchant, and some colors are different.
Later, I thought that only the outer skin is isolated between the battery core and the battery core, just in case an isolation material has to be added, such as epoxy board or highland barley paper. I bought less epoxy board, just add highland barley paper to each cell. Highland barley paper can also be insulated and resistant to high temperatures.
Paste the highland barley paper and then paste the double-sided tape. This process is very simple and does not take much time. The cells are to be used in series. You can use the positive and negative electrodes to be arranged alternately, and the positive and negative electrodes can also be arranged side by side, but the series line can only be crossed, so the series line will be longer and the internal resistance will be larger, so it is generally recommended. Use a cross arrangement. As mentioned earlier, there is a cell with a capacity of only 26AH. Put it on the sixth sheet. If it is placed on the first sheet, it will decay faster.
The cells are composed of two groups, one group is 9 pieces, and the other group is 8 pieces, for a total of 17 pieces. Use 5CM wide fiberglass tape to fix each group of cells. This fiberglass tape is very sticky and tough, and is very suitable for fixing batteries.
After wrapping two circles of tape, there is not much heat dissipation gap left, but this battery 1C will not heat up when placed, so there is no need to consider this problem.
The bottom of the cell should be in contact with the battery box, and a piece of highland barley paper or epoxy board should also be attached as a whole, and then attached with glass fiber tape, and the corners should be glued around to prevent wear.
An epoxy board is used to isolate the two sets of batteries. Double-sided tape and highland barley paper are not used here. Because the whole set is quite heavy, if the batteries are placed vertically in the future, the tape in the middle will be flattened.
Then fix the two sets of batteries together with fiberglass tape. There are 17 strings of cells, and there is an empty one on one side. If the Mavericks exceeded the voltage, it would prompt an error, so I would have directly assembled 18 strings. The left side is now empty. I didn't have anything else on hand, so I sawed a few pieces of wood and plugged it.
Then there is the welding part. At the beginning, I was going to use red copper sheets to connect. I used 1mm thick red copper sheets here. The internal resistance of red copper sheets is low, which is more suitable for connecting materials. The copper skin is thick, so I had to cut it casually with scissors.
It is easier to eat tin by making a gap in the copper sheet, but there is nothing to stabilize the copper sheet, so it is impossible to make a half hole, so I have to make a round hole on the side and then cut it open.
Cut the gap with scissors, and level the copper sheet to facilitate tinning. I don't care if it doesn't look good, anyway, I can't see it after it's soldered. Apply a layer of solder to the copper connection end to facilitate soldering. Then use a utility knife to randomly scratch the electrode nickel sheet, which makes it easier to eat tin, and use a cotton swab to apply a layer of flux.
Apply a layer of tin to the nickel sheet of each electrode first. When tinning, I covered the electrodes around the electrodes to prevent short circuits caused by misoperation or falling tin beads (there is only a distance of about 3mm between the electrodes and the shell). Note that a 200W soldering iron is used here, and the temperature is as high as 400°. The time on the electrode is as short as possible, no more than 1 second. Immediately after the soldering iron is removed, cover the electrode with a wet towel to prevent the high temperature from being instantly transferred to the inside of the battery and damage the chemical substances inside the battery.
The same is true during formal welding, block other places to prevent misoperation, pay attention to the temperature... It is best to weld the series strip between the two sets of batteries last, otherwise it may cause electric shock.
After soldering, because it cannot be soldered for a long time, the copper sheet only has to be pulled for one second after being pressed, and the solder joints are not good-looking like a cat gnawed. I also tried welding with a nickel piece and a copper piece. Even if the nickel piece is pulled off, the solder joint will not come off and it is very stable. It can be said that the biggest difficulty of DIY this battery is welding. Friends who are not good at welders should buy the kind that screw directly!
Once the battery is connected, the next step is to install the protective plate. Lithium batteries cannot be overcharged and overdischarged. Once overdischarged, the battery will be scrapped. Overcharging may cause accidents such as fire, so the protection board is essential. I bought the Yanyang BMS protection board here. The price is relatively expensive. I bought it mainly because it can be directly connected without cracking the protocol. All communications are isolated. The current I bought is the smallest 70A, which is enough.
Solder the protection board cable and power on the protection board for testing. Before energizing the protection board, check whether the connection is correct. Use a multimeter to measure one by one from the cable B-. The voltage is increased by 3.4V, indicating that there is no problem with the connection. The temperature sensor cable is covered with an asbestos tube in the middle. The temperature sensor cable is very thin. After aging, it may fall on the battery and burn the protective plate, so it must be covered.
After installing the protection board APP, turn on the power switch of the protection board and connect the protection board smoothly. The Yanyang protection board APP interface is relatively simple.
But you need to enter the parameter settings to set the parameters first. I set the battery type, capacity and number of strings. The parameters should be set according to the actual situation of the cell, and other parameters can be defaulted.
After the setting is completed, it can be seen in the real-time status that the protection board is working normally, the temperature sensor is normal, and the voltage of the cell is very consistent. The error is only 0.006V, which can be ignored.
Finally, 6 epoxy boards were sawed to wrap the battery, because the battery is to be placed in a stainless steel shell. The epoxy board has the characteristics of isolating high temperature, flame retardant and insulating, so it is very good for wrapping the battery.
After the modification is completed, the voltage of the cell is only 3.4V, which is almost no electricity. Please charge it first. What I use here is a modified Delta power supply for charging, the voltage can be adjusted from 1-120V, and the charging current can also support up to 12A. Lithium batteries are generally recommended to be charged at 0.2C, which means that this 55AH battery is best charged with a current of no more than 11A. The charging time is the capacity/current, but the current will become very small in the final stage, so generally an extra hour is added. It takes 6 hours to charge with 10A current, and 8 hours to charge with 8A current.
Ready to test mileage the next day. I ran 116KM under the condition of an adult, and there are a lot of climbing roads... After running 116km, there is still 21% of the battery left.
I continued to run the next day. After running for another 35KM, I finally ran out of electricity. I set the protection below 3V. I looked at the picture and it happened to be the battery with a capacity of only 26AH before, that is, the 6th string was put first. Out of power. The discharge capacity recorded by the protection board is 59AH, which is 3AH higher than the actual capacity of 56AH. It should be the credit of the E-ABS power recovery. The new 55AH battery and the original 20AH battery can run 200KM at a time without any problems.
Think about the original large lithium pack of Mavericks, the capacity is only 35AH, mine is 55AH, and the cost of making it is less than half of the large lithium pack... It seems that the battery made by myself is still very cost-effective.