There are several ways to wire multiple batteries to achieve the correct battery voltage or capacity for a particular DC installation. By connecting batteries in series or parallel or both as one big bank, rather than having individual banks will make your power source more efficient and will ensue maximum service life for your battery bank.
Wiring batteries together in series will increase the voltage while keeping the amp hour capacity the same.
- 2 x 6V 150Ah batteries wired in series will give you 12V, but only 150Ah capacity.
- 2 x 12V 150Ah batteries wired in series will give you 24V, but still only 150Ah.
Wiring batteries together in parallel has the effect of doubling capacity while keeping the voltage the same.
- 2 x 12V 150Ah batteries wired in parallel will give you only 12V, but increases capacity to 300Ah.
This is a combination of the above methods and is used for 2V, 6V or 12V batteries to achieve both a higher system voltage and capacity.
- 4 x 6V 150Ah batteries wired in series/parallel will give you 12V at 300Ah.
- 4 x 12V 150Ah batteries can be wired in series /parallel to give you 24V with 300Ah capacity.
Battery Cable Connections
The cables that join your batteries together play an important part in the performance of your battery bank. Choosing the correct size (diameter) and length of cable is important for overall efficiency. Cables that are too small or unnecessarily long will result in power loss and increased resistance.
When connecting batteries in series or parallel or series/parallel the cables between each battery should be of equal length. As you can see in the diagrams above, all the short cables connecting the batteries together are the same length and all the long cables are the same length. This links the batteries together with the same amount of cable resistance, ensuring that all batteries in the system are working equally together.
Particular attention should also be paid to where the main system cables are connected to the battery bank. More often than not, the system cables supplying the loads are connected to the first or “easiest” battery to get to in the bank, resulting in poor performance and service life. These main system cables that run to your DC distribution (loads) should be connected across the whole bank as illustrated in the diagrams to the left. This ensures the whole battery bank is charged and discharged equally, providing optimal performance.
The main system cables and the cables joining the batteries together should be of sufficient size (diameter) to handle the total system current. If you have a large battery charger or inverter you want to make sure that the cables are capable of carrying the potentially large currents that are generated or consumed by these pieces of equipment, as well as all your other loads.
Batteries are coupled in series to gain higher voltage, for instance 24 or even 48 Volt. The plus pole of each battery is connected to the minus pole of the following one, with the minus pole of the first battery and plus pole of the last battery connected to the system. This type of arrangement shown is a 24v, 120Ah bank.
Parallel coupling involves connecting the plus poles of multiple batteries to each other and the same with the minus poles. The plus of the first battery and the minus of the last battery are then connected to the system. This type of arrangement is used to increase capacity (in this case 12v 240Ah).
A combination of series and parallel connections is required if you need for example a 24 Volt battery set with a higher capacity. The battery should then be cross-wired to the system using the plus pole of the first and minus pole of the last battery. This type of arrangement shown is a 24v, 240Ah bank.