Series connection – we increase the voltage
A typical car battery has a voltage of 12V, and its capacity is between 50 and 100Ah. For the purposes of the following calculation, let’s assume that we have a battery with a capacity of 75Ah, and its maximum starting current is 750A. By connecting two such energy sources in series, we will double the voltage at the output of the system. It will no longer be 12V, but 24V. The series connection , however, does not raise the other values, namely capacity and starting current.
Batteries combined in this way should have:
- preferably the same capacity
- should be made with the same technology
- should be similarly worn out!
- The same state of charge.
- The cables used to connect the batteries must be properly sized and as short as possible.
- you should replace both batteries at the same time!
Parallel connection – we increase the capacity
Sometimes we need more capacity, while the voltage can remain at the same level. Then we connect batteries in parallel, which will allow us to achieve such parameters. Importantly, in this case we can connect batteries with different capacities and starting currents, but the level of their charge and voltage rating must be identical. When we use parallel connection, the latter value does not change, while capacities and currents add up. In the case of two 12V batteries, 75Ah and 750A, we will get an output voltage of 12V, a capacity of 150Ah and a maximum current of 1500A.
Batteries combined in this way should have:
- preferably the same capacity
- should be made with the same technology
- should be similarly worn out!
- The same state of charge.
- The cables used to connect the batteries must be properly sized and as short as possible.
- you should replace both batteries at the same time!
More of everything, i.e. series and parallel connection!
Wanting to increase both voltage and capacity, as well as the maximum currents of the system, we can use a series-parallel connection. It is usually used when we have four batteries. Assuming that they are still our previous 12V, 75Ah, 750A batteries, we first connect two of them in series, getting 24V voltage, 75Ah capacity and 750A current. Now we connect the two in series in parallel, giving us a final 24V, 150Ah and 1500A maximum current.
Batteries combined in this way should have:
- preferably the same capacity
- should be made with the same technology
- should be similarly worn out!
- The same state of charge.
- The cables used to connect the batteries must be properly sized and as short as possible.
- you should replace both batteries at the same time!
Is it worth replacing both batteries at the same time?
As the battery wears down, the internal resistance changes. The older the battery, the higher the internal resistance. If an “old” battery is connected to a “new” battery, the currents or voltages are distributed unevenly, resulting in asymmetrical loads. If the batteries are not discharged or charged, in the case of a parallel connection, compensating currents with high values flow between the batteries. “New” battery tries to charge “old” battery. (Potential equalization)*
*bannerbatterien
