When to Select a 12-, 24- or 48-Volt DC Battery System

What is the difference between 12-, 24- and 48-volt DC systems?

When entering into the off-grid and renewable energy industry, one of the first questions that will need to be answered is: What capacity and voltage configuration do I need for my battery bank? Electronic components all require different levels of energy and power, and understanding what quantity of power is needed for your inverter can seem not only tricky, but like guesswork in some circumstances. What’s the benefit of 12V vs. 48V inverters? Should you use a 24- or 48-volt solar system? Do you need 12 or 24 volts for your inverter? Which is the best inverter to get for 12V, 24V and 48V systems? With our informational guide (and a little help from our specialists if needed), you can find the answer to these questions and more.

First, what’s the difference between 12V vs. 24V vs. 48V inverters? Most inverters will fall into three categories for their input requirements: 12VDC, 24VDC and 48VDC. This is referring to the nominal DC voltage that the inverter will invert to AC voltage (i.e., 120VAC or 240VAC). There are multiple other AC supply voltages and configurations, but we will be generally referring 120VAC as it is the most widely available. Each of these types of inverters serve different purposes, and the nominal choice will depend heavily upon your purpose for purchase. But what’s the advantage of 24V over 12V or 48V anyways?

When to Use 12-Volt, 24-Volt or 48-Volt DC Systems

Deciding which one of these to go with can be extremely tedious and sometimes time consuming as the answers to this question can be quite ambiguous. As a result, asking if a 12V or 24V inverter is better becomes a question that cannot be answered. The reason being is each system has its own set of unique variables that makes it impossible to provide a single answer. Therefore, we find it is much more efficient to provide the answer to: Why would one choose a 12VDC, 24VDC or 48VDC power system? There’s only one answer: electrical resistance. Electrical resistance is a measure of the ease or difficulty it takes for an electrical current to flow through a conductive material, which is a fundamental property inherit to all electrical devices. For all intents and purposes, resistance is equivalent to heat caused by friction on a particle scale.

Having more resistance will cause a rise in heat. Heat in electric circuits is bad – not only can it damage equipment, but it can be a fire hazard. To reduce this amount of resistance (or heat) in a circuit, we sometimes can use a bigger conductor (aka cable) or even different material compositions. However, there is a limit to the size of cable you would be able to find/purchase that would still be capable of handling the amperage that comes with larger power draws. For example, a fuse rated for 10A is around $1, whereas a 1000A fuse is roughly $396.00. While it can be tempting to select a less expensive cable for your needs, it is vital to choose the appropriate cable in order to avoid fire hazards. This is obviously just one example of pricing as a factor of higher amperage, but size issues and ease of installation are very close behind in terms of impact. This is where we look to higher nominal DCV inputs.

How to Calculate Your Continuous Power Rating

Ohm’s law tells us that Power is the product of Voltage and Current in a given circuit (Watts = Volts * Amps). With this, we can use some basic algebra to work out exactly what nominal voltage we should be using for your system.

First, I would like to break down this formula into portions relative to our conversation. Watts, or Power, should be calculated based on the actual power ratings for the electronic devices you wish to power using an inverter. Usually, this number will be located on the power cord or the nameplate of the device. Gathering the proper values of wattage and power are important for making an accurate estimate for your inverter size and efficiency. Once you have these numbers, you will want to add together the values for any devices that would be powered at the same time, this will be the number you use to pick the size of inverter you will need (e.g., if you had a 50W fan, 250W TV and 200W DVD player that would be running at the same time, you would need at least a 500W inverter). For more information on selecting the right inverter size, you can find a helpful guide here.

Adding your total wattage together results in your continuous or consistent power rating. This is the amount of power that is required from your inverter to charge all of your devices simultaneously over a stretch of time. However, your continuous rating is not the only important factor in selecting an inverter for size – you also need to consider your equipment’s peak rating. The peak power rating, unlike the continuous power rating, is the maximum power required by your inverter to start up your devices. Many appliances and devices will require more power to boot up than their continuous power, and while many inverters supply a higher peak rating, it’s best to not rely on this as it can wear out your inverter prematurely. The safest choice is to identify your continuous power rating and double it – this will allow you to choose an inverter that has more than enough power for your equipment’s continuous and peak needs.

Determining Your System’s Amperage

Once you have calculated your total wattage need, you will want to pick a nominal voltage for your battery bank. This can be done arbitrarily at first to simply check what the amperage would be in different configurations or based on external variables, such as only having one battery available. In order to find out the proper amount of batteries for your inverter, you’ll need to do some more measurements, which are explained in another of The Inverter Store’s convenient posts. Regardless, once you have the power and voltage values, we can then move on to calculating the amperage which by proxy will tell us how large our conductors should be and the ratings for components such as fuses, breakers, lugs and the composition thereof.

To calculate the amperage of your chosen DC configuration, you will need to modify Ohm’s Law to fit our needs. Skipping the mathematical instruction, the resulting equation is W ÷ V = A. For example, if we had a need of 6000W and we want to use 12V as our DC source, this would give us an Amperage rating of 500A. This doesn’t sound terrible at first, until you attempt to find a cable size capable of supplying that amount of current and see the price per foot. There are obviously ways to accommodate this set up; connecting multiple cables to each lug or finding cables and fuses that are capable of carrying the necessary amperage, but the easiest and most efficient solution is to simply raise the DC voltage. When operating with heavy electrical equipment, overestimating the amount of power needed will be the safest solution in order to avoid fire hazards and malfunctions. Again referencing our equation W ÷ V = A, we can see that raising the voltage by a factor of two reduces the amperage by half.

6000W ÷ 12V = 500A vs. 6000W ÷ 24V = 250A vs. 6000W ÷ 48V = 125A

By decreasing the amount of amperage in the DC circuit, there will be a wider range of products such as cables and fuses, available for your specific configuration. This may be necessary depending on the off-grid power system you’re operating with.

Hopefully with these helpful tips you’ll be able to select between 12-volt vs. 24-volt vs. 48-volt systems for your project. When selecting a 12-volt or 24-volt battery, it’s important to make proper calculations for the optimum system. However, selecting between a 12-, 24- or 48-volt system is only one step in the process. It will also be important to learn how to set up your battery systems in parallel vs. in sequence, as well as understanding what type of inverter you need to use for your project. You can find guides for these decisions and much more in The Inverter Store’s helpful tips section.