Semi-truck electrical systems are designed to utilize four large 12V batteries to achieve both 24V and 12V outputs effectively.
To produce 24V, the batteries are connected in series. This means that the positive terminal of one battery is connected to the negative terminal of the next battery. For example, if you connect two 12V batteries in series, you add their voltages together (12V + 12V), resulting in a total of 24V. In a typical semitractor truck setup, two pairs of batteries are connected in series (creating two sets of 24V), and these pairs are then connected in parallel, which effectively maintains the capacity while allowing the truck to have a stable 24V supply when needed for the starter motor and other high-draw components.
On the other hand, to obtain 12V from the system, you can simply use one of the pairs alone (a single 12V battery) or tap into the parallel configuration where all batteries contribute to the 12V components. This allows the truck’s lighter electrical components, like lights and radios, to run efficiently.
One of the significant advantages of using a 24V system in semitractor trucks is efficiency. Higher voltage systems can reduce current draw for the same amount of power, which means less energy is lost as heat in the wiring. This results in smaller, lighter wiring, as higher voltages enable the use of thinner wires. Moreover, a 24V system provides better starting power to the large diesel engines, especially in colder conditions, making it easier to start the truck and improving overall performance.