Lithium Battery Series And Parallel Instructions
Introduction:
The series and parallel connection of lithium batteries is very common, but there are many things to pay attention to. Otherwise, it is easy to have safety hazards. Let us systematically sort out this related knowledge from all levels.
Under what circumstances do we need series or parallel connection?
For example, when you want more power, you may want to connect them in parallel. When you want to get higher voltages, you may want to connect them in series. If you connect them both in series and parallel, you can increase the voltage while also increasing the capacity of the entire system.
How many ways are there to connect the battery?
Standard connection methods include series, parallel, and series-parallel.
What is a series circuit?
As shown in the figure below, We can understand this concept in conjunction with the road. If there is only one path for the entire circuit and no other choice for the movement of electrons, then the circuit is a series circuit. It is worth noting that a series circuit is sometimes only a small part of the entire circuit, because other parts may be connected in parallel, and only a small part is connected in series. This is a small detail that everyone needs to pay attention to.
What are the characteristics of series circuits?
All currents in a series circuit are the same.
The total voltage in a series circuit is the sum of the voltages across all resistors.
When batteries are used in series, once one of the batteries is exhausted and causes the BMS to shut down the circuit, the entire circuit will become unusable.
The total resistance of a series circuit is equal to the sum of all partial resistances.
Can lithium batteries of different voltages be connected in series?
This situation is unacceptable. Each lithium battery has a BMS inside, and the BMS contains a MOS tube. Since the MOS tubes inside the BMS with different voltages have different maximum withstand voltage values, if lithium batteries with different voltages are connected in series, the MOS tube with a lower withstand voltage value will Easily be damaged first, causing the BMS to be burned directly and unable to work normally.
Under what circumstances can lithium batteries be connected in series?
When the lithium battery types are the same, for example, they are all 3.2V lithium iron phosphate batteries, or they are all 3.7V lithium-ion batteries, or they are all polymer batteries.
When the voltages are the same, for example, 12V and 12V are connected in series, 24V and 24V are connected in series, and 48V and 48V are connected in series.
When the capacity is the same, for example, they are all 100Ah in series, or they are all 200Ah in series.
When the newness and oldness are the same, for example, they are all new batteries, or they are all old batteries used in the same batch.
The most important and easily overlooked point is that even if we use the same battery, even if the model, voltage, and capacity are the same, we cannot directly connect them in series. Ensure that the SOC is consistent when connected in series; for example, both have 95% of the remaining power, or both have 80% of the remaining power. The power difference should not exceed 2%. This can maximize the balance of the battery packs when connected in series.
Under what circumstances would we want to use batteries in series?
Suppose you bought four 12V 100Ah LiFePo4 battery packs, but the inverter in your home is 48V. Do you need to buy another 48V battery pack? Not necessary, connect four 12V 100Ah battery packs in series to become 48V 100Ah, which can be used with a 48V inverter. In the same way, if you need a higher voltage platform, you can continue to connect in series, such as 24V, 36V, 48V, 60V, 72V, 84V, etc., but be aware that you must first confirm with the manufacturer. Whether series connection is allowed is determined internally by the BMS. It is determined by the maximum withstand voltage value of the MOS tube, and the data of each brand is different.
Charging in series circuit
When battery packs are used in series, we can charge the whole without using a charger to charge each battery pack separately. This is a quick and easy way to save time and energy, and you don’t need to buy a lot of chargers to save costs.
However, the series circuit has a limitation. That is, if any battery in the circuit is automatically disconnected after being fully charged, other batteries will not be able to continue charging. This is easy to understand because if you continue to charge, the already fully charged battery will be at risk of overcharging.
Why does one battery always get fully charged first in a series circuit?
You may be confused, wouldn’t it be great if it could be fully charged together? The theory is indeed like this, but in fact, the charging speed depends on the capacity of each lithium battery, the state of the cell, and the decaying state of the internal pack. Each battery is unique, and we can only try to make their parameters identical. However, complete consistency cannot be guaranteed. New batteries may have almost the same capacity, but as the battery is used, the aging curve of the battery will be different. Especially after the battery has been used for many years, the capacity of some batteries will suddenly decay rapidly. When this happens, the capacity will be small. The battery is easier to charge, and when it is fully charged, the remaining batteries cannot continue to be charged, even if they are not fully charged.
Why does the battery automatically disconnect when fully charged? Who controls it?
The BMS controls this inside the battery. The BMS has many acquisition lines. These lines can detect the voltage of each cell. By analyzing these voltage data, the BMS can know whether it is full. When the BMS detects that the voltage reaches the set value, The circuit will be turned off to avoid overcharging caused by continued charging.
What is a parallel circuit?
As shown in the figure below, If there are multiple paths to choose from when an electron moves, then the circuit is a parallel circuit. It is worth noting that a parallel circuit is sometimes only a small part of the entire circuit because other parts may be connected in series, but only a small part is connected in parallel. This is a small detail that everyone needs to pay attention to.
What are the characteristics of parallel circuits?
The total current in a parallel circuit equals the sum of the currents in all branches.
The total voltage of a parallel circuit is the same
When batteries are used in parallel, once one is out of energy and the BMS shuts down the circuit, it will not affect the other batteries, and the charging process will not affect the other batteries.
The reciprocal of the total resistance of a parallel circuit is equal to the sum of the reciprocals of the partial resistances of all branches.
Can lithium batteries of different voltages be connected in parallel?
This is also not possible. It is different from the reason for series connection. If batteries of different voltages are connected in parallel, the high-voltage battery may spontaneously charge the low-voltage battery. On the one hand, the low-voltage battery generates serious heat, and on the other hand, it also wastes energy.
In addition, batteries with different voltages have different discharge curves different performances, and may also have different energy densities, which will further increase the voltage difference. At the same time, if the battery is charged under this condition, if the voltage difference is too large, it may directly damage the low-voltage battery. In severe cases, it may directly cause a large amount of heat or explosion.
Under what circumstances can lithium batteries be connected in parallel?
When the lithium battery types are the same, for example, they are all 3.2V lithium iron phosphate batteries, or they are all 3.7V lithium-ion batteries, or they are all polymer batteries.
When the voltages are the same, for example, 12V and 12V are connected in series, 24V and 24V are connected in series, and 48V and 48V are connected in series.
When the capacity is the same, for example, they are all 100Ah in series, or they are all 200Ah in series.
When the newness and oldness are the same, for example, they are all new batteries, or they are all old batteries used in the same batch.
The SOC when connected in parallel is the same. For example, both have 95% remaining power, or both have 80% remaining power. The power difference should not exceed 2%. This can maximize the balance of the battery packs when connected in parallel.
Under what circumstances would we want to use batteries in parallel?
Suppose you buy two sets of 48V 100Ah lithium-ion batteries. You can directly connect them in parallel to become 48V 200Ah. This way you have more power, which means you can use it longer.
When do we need to use batteries in series and parallel?
Suppose you have 16 12V 50Ah battery packs of the same brand, model, and batch. At this time you want to increase the voltage; for example, you want to use 48V instead of 12V, and you also want the battery capacity to be as large as possible.
Then you can connect 4 batteries in series to form 48V 50Ah, then connect these 4 48V 50Ah batteries in parallel to get 48V 200Ah.
You may find that I can connect them parallel to form 12V 200Ah and then connect these four 12V 200Ah in series. Can it also become 48V 200Ah?
This is indeed the case, but there are some differences:
Advantages of parallel connection first and then series connection:
As we mentioned above, in a parallel circuit, damage to one of the batteries will only lead to a reduction in capacity and will not affect the work of the entire system. Therefore, this method can minimize the impact of a single battery pack on the entire system. It is worth noting that we usually add circuit breakers in parallel circuits to ensure that the current in a single parallel circuit is too large.
What are the disadvantages of connecting in parallel first and then in series:
Although connecting in series and then in parallel can ensure the regular operation of the system to the greatest extent, this method can easily lead to excessive current in a single circuit, which frequently causes battery balancing problems, and later has to spend a lot of time dealing with balance problems.
What are the advantages of connecting in series first and then in parallel:
However, this method requires all batteries to work correctly because once any battery shuts down because it is fully charged or discharged, the entire system will not work. This method is very friendly to the consistency of the entire system because all The batteries can be charged and discharged simultaneously, which also facilitates later troubleshooting.
Electrical knowledge about series circuits and parallel circuits
| Dimension | Series Circuit | Parallel Circuit |
| Current | Total current I is the same across all components, i.e., I=I1=I2=I3=…=In | Total current I is the sum of branch currents, i.e., I=I1+I2+I3+…+In |
| Voltage | Total voltage V is the sum of component voltages, i.e., V=V1+V2+V3+…+Vn | Total voltage V is the same across all branches, i.e., V=V1=V2=V3=…=Vn |
| Resistance | Total resistance R is the sum of component resistances, i.e., R=R1+R2+R3+…+Rn | The reciprocal of total resistance R is the sum of the reciprocals of branch resistances, i.e., 1/R=1/R1+1/R2+1/R3+…+1/Rn |
| Heat Generation | Total heat generation Q is related to total current I, total resistance R, and time t, i.e., Q=I2Rt | Total heat generation Q is related to total current I, total resistance R, and time t, i.e., Q=I2Rt |
| Equivalent Resistance | Larger resistance restricts current flow, affecting the overall circuit performance, denoted by R | Smaller resistance restricts current flow, affecting the overall circuit performance, denoted by R |
| Effect of Component Failure | A failure in one component disrupts the entire circuit, halting current flow | A failure in one component does not disrupt the entire circuit, and current can continue to flow |
| Total Current | The same total current I flows through all components | Total current is divided into different branches, and each branch has its own current, i.e., I=I1=I2=I3=…=In |
| Total Voltage | Total voltage V is divided among components, with each component having the same voltage, i.e., V=V1=V2=V3=…=Vn | Total voltage is the same across all branches, i.e., V=V1=V2=V3=…=Vn |
| Total Power Loss | Total power loss P is related to total current I, total resistance R, and time t, i.e., P=I2Rt | Total power loss P is related to total current I, total resistance R, and time t, i.e., P=I2Rt |
Author Profile
Thomas Chen
Thomas Chen is a seasoned expert in the new energy industry, with a focus on lithium battery technology. A Shenzhen University alumnus, class of 2010, Thomas has cultivated a wealth of experience through pivotal roles at EVE and BYD. Renowned for his profound insights into the sector, he possesses a unique aptitude for identifying market trends and understanding customer needs. His articles offer a distinctive perspective, drawn from a rich background in the field.
Introduction:
The series and parallel connection of lithium batteries is very common, but there are many things to pay attention to. Otherwise, it is easy to have safety hazards. Let us systematically sort out this related knowledge from all levels.
Under what circumstances do we need series or parallel connection?
For example, when you want more power, you may want to connect them in parallel. When you want to get higher voltages, you may want to connect them in series. If you connect them both in series and parallel, you can increase the voltage while also increasing the capacity of the entire system.
How many ways are there to connect the battery?
Standard connection methods include series, parallel, and series-parallel.
What is a series circuit?
As shown in the figure below, We can understand this concept in conjunction with the road. If there is only one path for the entire circuit and no other choice for the movement of electrons, then the circuit is a series circuit. It is worth noting that a series circuit is sometimes only a small part of the entire circuit, because other parts may be connected in parallel, and only a small part is connected in series. This is a small detail that everyone needs to pay attention to.
What are the characteristics of series circuits?
All currents in a series circuit are the same.
The total voltage in a series circuit is the sum of the voltages across all resistors.
When batteries are used in series, once one of the batteries is exhausted and causes the BMS to shut down the circuit, the entire circuit will become unusable.
The total resistance of a series circuit is equal to the sum of all partial resistances.
Can lithium batteries of different voltages be connected in series?
This situation is unacceptable. Each lithium battery has a BMS inside, and the BMS contains a MOS tube. Since the MOS tubes inside the BMS with different voltages have different maximum withstand voltage values, if lithium batteries with different voltages are connected in series, the MOS tube with a lower withstand voltage value will Easily be damaged first, causing the BMS to be burned directly and unable to work normally.
Under what circumstances can lithium batteries be connected in series?
When the lithium battery types are the same, for example, they are all 3.2V lithium iron phosphate batteries, or they are all 3.7V lithium-ion batteries, or they are all polymer batteries.
When the voltages are the same, for example, 12V and 12V are connected in series, 24V and 24V are connected in series, and 48V and 48V are connected in series.
When the capacity is the same, for example, they are all 100Ah in series, or they are all 200Ah in series.
When the newness and oldness are the same, for example, they are all new batteries, or they are all old batteries used in the same batch.
The most important and easily overlooked point is that even if we use the same battery, even if the model, voltage, and capacity are the same, we cannot directly connect them in series. Ensure that the SOC is consistent when connected in series; for example, both have 95% of the remaining power, or both have 80% of the remaining power. The power difference should not exceed 2%. This can maximize the balance of the battery packs when connected in series.
Under what circumstances would we want to use batteries in series?
Suppose you bought four 12V 100Ah LiFePo4 battery packs, but the inverter in your home is 48V. Do you need to buy another 48V battery pack? Not necessary, connect four 12V 100Ah battery packs in series to become 48V 100Ah, which can be used with a 48V inverter. In the same way, if you need a higher voltage platform, you can continue to connect in series, such as 24V, 36V, 48V, 60V, 72V, 84V, etc., but be aware that you must first confirm with the manufacturer. Whether series connection is allowed is determined internally by the BMS. It is determined by the maximum withstand voltage value of the MOS tube, and the data of each brand is different.
Charging in series circuit
When battery packs are used in series, we can charge the whole without using a charger to charge each battery pack separately. This is a quick and easy way to save time and energy, and you don’t need to buy a lot of chargers to save costs.
However, the series circuit has a limitation. That is, if any battery in the circuit is automatically disconnected after being fully charged, other batteries will not be able to continue charging. This is easy to understand because if you continue to charge, the already fully charged battery will be at risk of overcharging.
Why does one battery always get fully charged first in a series circuit?
You may be confused, wouldn’t it be great if it could be fully charged together? The theory is indeed like this, but in fact, the charging speed depends on the capacity of each lithium battery, the state of the cell, and the decaying state of the internal pack. Each battery is unique, and we can only try to make their parameters identical. However, complete consistency cannot be guaranteed. New batteries may have almost the same capacity, but as the battery is used, the aging curve of the battery will be different. Especially after the battery has been used for many years, the capacity of some batteries will suddenly decay rapidly. When this happens, the capacity will be small. The battery is easier to charge, and when it is fully charged, the remaining batteries cannot continue to be charged, even if they are not fully charged.
Why does the battery automatically disconnect when fully charged? Who controls it?
The BMS controls this inside the battery. The BMS has many acquisition lines. These lines can detect the voltage of each cell. By analyzing these voltage data, the BMS can know whether it is full. When the BMS detects that the voltage reaches the set value, The circuit will be turned off to avoid overcharging caused by continued charging.
What is a parallel circuit?
As shown in the figure below, If there are multiple paths to choose from when an electron moves, then the circuit is a parallel circuit. It is worth noting that a parallel circuit is sometimes only a small part of the entire circuit because other parts may be connected in series, but only a small part is connected in parallel. This is a small detail that everyone needs to pay attention to.
What are the characteristics of parallel circuits?
The total current in a parallel circuit equals the sum of the currents in all branches.
The total voltage of a parallel circuit is the same
When batteries are used in parallel, once one is out of energy and the BMS shuts down the circuit, it will not affect the other batteries, and the charging process will not affect the other batteries.
The reciprocal of the total resistance of a parallel circuit is equal to the sum of the reciprocals of the partial resistances of all branches.
Can lithium batteries of different voltages be connected in parallel?
This is also not possible. It is different from the reason for series connection. If batteries of different voltages are connected in parallel, the high-voltage battery may spontaneously charge the low-voltage battery. On the one hand, the low-voltage battery generates serious heat, and on the other hand, it also wastes energy.
In addition, batteries with different voltages have different discharge curves different performances, and may also have different energy densities, which will further increase the voltage difference. At the same time, if the battery is charged under this condition, if the voltage difference is too large, it may directly damage the low-voltage battery. In severe cases, it may directly cause a large amount of heat or explosion.
Under what circumstances can lithium batteries be connected in parallel?
When the lithium battery types are the same, for example, they are all 3.2V lithium iron phosphate batteries, or they are all 3.7V lithium-ion batteries, or they are all polymer batteries.
When the voltages are the same, for example, 12V and 12V are connected in series, 24V and 24V are connected in series, and 48V and 48V are connected in series.
When the capacity is the same, for example, they are all 100Ah in series, or they are all 200Ah in series.
When the newness and oldness are the same, for example, they are all new batteries, or they are all old batteries used in the same batch.
The SOC when connected in parallel is the same. For example, both have 95% remaining power, or both have 80% remaining power. The power difference should not exceed 2%. This can maximize the balance of the battery packs when connected in parallel.
Under what circumstances would we want to use batteries in parallel?
Suppose you buy two sets of 48V 100Ah lithium-ion batteries. You can directly connect them in parallel to become 48V 200Ah. This way you have more power, which means you can use it longer.
When do we need to use batteries in series and parallel?
Suppose you have 16 12V 50Ah battery packs of the same brand, model, and batch. At this time you want to increase the voltage; for example, you want to use 48V instead of 12V, and you also want the battery capacity to be as large as possible.
Then you can connect 4 batteries in series to form 48V 50Ah, then connect these 4 48V 50Ah batteries in parallel to get 48V 200Ah.
You may find that I can connect them parallel to form 12V 200Ah and then connect these four 12V 200Ah in series. Can it also become 48V 200Ah?
This is indeed the case, but there are some differences:
Advantages of parallel connection first and then series connection:
As we mentioned above, in a parallel circuit, damage to one of the batteries will only lead to a reduction in capacity and will not affect the work of the entire system. Therefore, this method can minimize the impact of a single battery pack on the entire system. It is worth noting that we usually add circuit breakers in parallel circuits to ensure that the current in a single parallel circuit is too large.
What are the disadvantages of connecting in parallel first and then in series:
Although connecting in series and then in parallel can ensure the regular operation of the system to the greatest extent, this method can easily lead to excessive current in a single circuit, which frequently causes battery balancing problems, and later has to spend a lot of time dealing with balance problems.
What are the advantages of connecting in series first and then in parallel:
However, this method requires all batteries to work correctly because once any battery shuts down because it is fully charged or discharged, the entire system will not work. This method is very friendly to the consistency of the entire system because all The batteries can be charged and discharged simultaneously, which also facilitates later troubleshooting.
Electrical knowledge about series circuits and parallel circuits
| Dimension | Series Circuit | Parallel Circuit |
| Current | Total current I is the same across all components, i.e., I=I1=I2=I3=…=In | Total current I is the sum of branch currents, i.e., I=I1+I2+I3+…+In |
| Voltage | Total voltage V is the sum of component voltages, i.e., V=V1+V2+V3+…+Vn | Total voltage V is the same across all branches, i.e., V=V1=V2=V3=…=Vn |
| Resistance | Total resistance R is the sum of component resistances, i.e., R=R1+R2+R3+…+Rn | The reciprocal of total resistance R is the sum of the reciprocals of branch resistances, i.e., 1/R=1/R1+1/R2+1/R3+…+1/Rn |
| Heat Generation | Total heat generation Q is related to total current I, total resistance R, and time t, i.e., Q=I2Rt | Total heat generation Q is related to total current I, total resistance R, and time t, i.e., Q=I2Rt |
| Equivalent Resistance | Larger resistance restricts current flow, affecting the overall circuit performance, denoted by R | Smaller resistance restricts current flow, affecting the overall circuit performance, denoted by R |
| Effect of Component Failure | A failure in one component disrupts the entire circuit, halting current flow | A failure in one component does not disrupt the entire circuit, and current can continue to flow |
| Total Current | The same total current I flows through all components | Total current is divided into different branches, and each branch has its own current, i.e., I=I1=I2=I3=…=In |
| Total Voltage | Total voltage V is divided among components, with each component having the same voltage, i.e., V=V1=V2=V3=…=Vn | Total voltage is the same across all branches, i.e., V=V1=V2=V3=…=Vn |
| Total Power Loss | Total power loss P is related to total current I, total resistance R, and time t, i.e., P=I2Rt | Total power loss P is related to total current I, total resistance R, and time t, i.e., P=I2Rt |
Author Profile
Thomas Chen
Thomas Chen is a seasoned expert in the new energy industry, with a focus on lithium battery technology. A Shenzhen University alumnus, class of 2010, Thomas has cultivated a wealth of experience through pivotal roles at EVE and BYD. Renowned for his profound insights into the sector, he possesses a unique aptitude for identifying market trends and understanding customer needs. His articles offer a distinctive perspective, drawn from a rich background in the field.
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