Battery wiring

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In a battery bank with only series connections, there is only one path for the current to flow. It may be necessary to connect more than one series string of batteries with a parallel connection in a battery bank to achieve a desired amount of energy storage capacity. If there are two parallel strings of batteries, it means that any current entering or exiting the battery bank has the choice of two different paths that it can take. Current always has a preference for the path of lowest resistance, so if one of the parallel paths has higher resistance (longer or smaller size wire) then less current will follow that path. This can mean that one parallel string of the batteries will have to work much harder and will ultimately fail prematurely. Therefore, it is very important to try to design a battery bank to use only one series string of batteries or to make sure that the wiring in th battery bank is done properly.

In well-developed solar markets, there is a large range of different battery voltages (2V-12V) and Ah ratings (more than 4000Ah) that make possible a variety of battery bank designs. In less developed markets only 12V deep-cycle batteries may be available and as PV system sizes increase so will the number of parallel strings. It is also often the case that certain inverters and charge controllers are not available in 48V designs. In any case, it is ideal to keep the number of parallel strings to 3 or less if possible as ensuring balanced charging and discharging becomes more complicated with each additional parallel battery string.

Battery bank wiring practices

It is best to cut and add the terminals to all of the wires for a battery bank before installing them to ensure proper lengths.

All wires used for series connections in a battery bank should be the same wire gauge.
All wires used for parallel connections in a battery bank should be the same wire gauge.
All wires used for series connections in a battery bank should be the same length.
All wires used for parallel connections in a battery bank should be the same length.

It is important to choose the correct terminals for the wire that is being used in order to ensure a solid connection with minimal resistance.

4 x 12V FLA batteries connected in series to create a 48V battery bank.
2 x 12V FLA batteries connected in series in two parallel strings to create a 24V battery bank.
4 x 12V FLA batteries connected in series in two parallel strings to create a 48V battery bank.
4 x 12V FLA batteries connected in series in three parallel strings to create a 48V battery bank.