Pls can you explain what happens when you connect two cells in parallel? Thx
Pls can you explain what happens when you connect two cells in parallel? Thx
When you connect two identical batteries in parallel, you double the output capacity while keep the output voltage the same as either battery. In the other case, if two identical batteries are connected in series, the output voltage is doubled but the output capacity is kept the same as either battery. In both cases, the output energy is doubled.
Both series and parallel connects are very common when a single battery (or cell) cannot do the job.
For example, the battery pack in the laptop consists of multiple cells (lithium-ion batteries). There can be 6-cell battery pack with 3 in series and two groups of the 3 cells in parallel. This way the output voltage can be 11.1V (3 by 3.7V) and the output capacity can be 4400 mAh (2 by 2200 mAh). There also can be 9-cell battery pack with 3 in series and three groups of the 3 cells in parallel. So 11.1V and 6600 mAh. So on and so forth.
Same is true for electric car battery packs. The 24 kWh Nissan LEAF uses 192 of 33.1 Ah cells in its battery pack. 96 of such cells are put in series to output 360 V. Two groups of the 96 cells are connected in parallel. There is some interesting data on cell capacity, energy density and range on
If the two cells connected in parallel are not identical, a few things can happen, as addressed in other answers. Firstly, the voltage of the cells will be balanced. Secondly, the difference in cell properties such as internal resistance will affect how the current goes in and out of each cell. Thirdly, if one cell is shorted, it can drain the other cell.
In comparison, when two different cells in series are being used, the voltage of each cell can be different and one cell can reach end of (dis)charge faster than the other cell. The voltage of each cell will not be balanced instantaneously.
EV battery packs consists of hundreds and even thousands of cells. The cells are graded to be quite close to being identical, but are still different, and even more different as the cells age. So it is crucial for the battery management system to monitor, balance and control each individual cell.
When you connect two identical batteries in parallel, you double the output capacity while keep the output voltage the same as either battery. In the other case, if two identical batteries are connected in series, the output voltage is doubled but the output capacity is kept the same as either battery. In both cases, the output energy is doubled.
Both series and parallel connects are very common when a single battery (or cell) cannot do the job.
For example, the battery pack in the laptop consists of multiple cells (lithium-ion batteries). There can be 6-cell battery pack with 3 in series and two groups of the 3 cells in parallel. This way the output voltage can be 11.1V (3 by 3.7V) and the output capacity can be 4400 mAh (2 by 2200 mAh). There also can be 9-cell battery pack with 3 in series and three groups of the 3 cells in parallel. So 11.1V and 6600 mAh. So on and so forth.
Same is true for electric car battery packs. The 24 kWh Nissan LEAF uses 192 of 33.1 Ah cells in its battery pack. 96 of such cells are put in series to output 360 V. Two groups of the 96 cells are connected in parallel. There is some interesting data on cell capacity, energy density and range on
If the two cells connected in parallel are not identical, a few things can happen, as addressed in other answers. Firstly, the voltage of the cells will be balanced. Secondly, the difference in cell properties such as internal resistance will affect how the current goes in and out of each cell. Thirdly, if one cell is shorted, it can drain the other cell.
In comparison, when two different cells in series are being used, the voltage of each cell can be different and one cell can reach end of (dis)charge faster than the other cell. The voltage of each cell will not be balanced instantaneously.
EV battery packs consists of hundreds and even thousands of cells. The cells are graded to be quite close to being identical, but are still different, and even more different as the cells age. So it is crucial for the battery management system to monitor, balance and control each individual cell.
