Pretty much all of us use batteries in our daily lives. They are in our remote control, in our kitchen clock, in our car, or in our camper. For those who haven’t looked into DC systems for RVs, boats, or off-grid applications, chances are they haven’t had to worry about battery voltage either. However, when you think about a mobile power supply, you cannot get past a decision between 12 V and 24 V battery systems.
What is the voltage of the electrical system of a car, RV, or boat?
The basic knowledge of a battery system is understanding voltage (measured in volts). Voltage is the amount of electrical pressure required to transmit an electrical current. Most vehicles, i.e., cars, mobile homes, and boats, use 12-volt battery systems. Twelve volts means the battery can deliver a maximum output of 12.8 volts. A 24-volt battery system can deliver a maximum output of 25.6 volts. Twelve-volt batteries are used in most vehicles because the electrical components, such as the starter, lights, and ignition, are designed to work with 12 volts. The 12-volt nominal voltage can be slightly higher or lower depending on the state of charge and load.
How is a 24-volt battery system structured?
In larger trucks and buses, 24-volt battery systems are sometimes used because the vehicles have higher power requirements, and long cables must be laid. Twenty-four-volt battery systems are also used in larger boats and some mobile homes with complex solar systems. There are several ways to build this. One option is to buy a 24-volt battery. However, these are not widespread and, therefore, difficult to obtain. In addition, they are comparatively expensive. The other is to connect two 12-volt leisure batteries in series. However, two batteries take up more space than one, so a single 24-volt battery may be a better choice if space is an issue.
How are 12-volt batteries connected in series?
As previously mentioned, the most common way to set up a 24-volt battery system is to connect two 12-volt batteries in series. When connected in series, the voltage increases with each battery. With our WATTSTUNDE batteries, a maximum of 4 can be connected, which can vary with other manufacturers. The negative pole of one battery is connected to the positive pole of the other battery. This means that the same current flows through all interconnected batteries. For example, if two batteries, each with 100 Ah and 12 volts, are connected in series, the result is a voltage of 24 volts with a capacity of 100 Ah. This means that when connected in series, the voltage adds up, and the storage capacity remains the same.
Comparison between 12-volt and 24-volt battery systems
When considering 12-volt and 24-volt battery systems, there are pros and cons for both system types. As already mentioned, 12-volt battery systems are relatively widespread. In addition to the components used to operate the vehicles, which in most cases are designed for 12 volts, most devices, such as refrigerators and all the lighting in the caravan, also work with 12 volts. Twelve-volt systems only require one battery and are well suited for applications with low power consumption and short cable lengths. Most RV units will work with them, and smaller solar systems are easily connected. Twenty-four-volt battery systems are advantageous because you use a smaller diameter cable, reducing the wiring cost and the space required to route the cables. This is particularly important when long cable runs are required. It may sound surprising at first that more voltage can flow through a thinner cable. A higher voltage requires less current to generate the same power. Since we need less current (measured in amperes) with 24V lithium battery systems, we can use a smaller cable. This is why very high-voltage electricity is transmitted over power lines. The wires can be very thin and carry a lot more current. Twelve-volt battery systems would require massive cables if they had to transfer large loads as the current (amps) is higher. For example, higher voltages, such as 24 volts, are more advantageous if you have larger solar systems in your caravan. The biggest disadvantage of 24-volt batteries is that various devices are designed for 12 volts. When using 12-volt devices, a converter (DC-DC converter) is required, which reduces the voltage to 12 volts. While this voltage converter works very well and provides a stable voltage, it causes additional costs and an energy loss of about 4%.
Determine energy needs
To set up a battery system, you must know your energy requirements for operating the required devices. The energy consumed by a device is measured in watts. Once you know your needs, you can determine the required system. As a guide: If you need less than 3000 watts (in alternating current), you can usually get by with a 12-volt battery system. If you need more, a 24-volt battery system is recommended. If your power consumption is even higher, i.e., over 6000 watts, you will benefit from an even larger DC system and an upgrade to 48 volts. For stand-alone systems, for example, 48 volts can make perfect sense. There are many variables to consider when deciding which system is best. Once you have identified your needs and the type of consumer, you can make an informed decision.