In order to connect the CCTV cameras it’s necessary to use a power supply that provides the voltage and the current according to the designed security system. In this article, we will discuss how to choose the correct power supply for your surveillance cameras. In most modern installations with analog cameras, the power supply is centralized and distributes power to all installed cameras. Below is an example of a centralized power supply, this type of power supply can be used to power up multiple cameras according to their specifications.
The connection is extremely simple because there are labels on each of the connectors, the power supply must be connected to an electrical outlet using the hot and neutral connectors, and the positive and negative connectors are connected to the cameras. There is also a connector for grounding. It is recommended to use a power supply up to 80% of its maximum capacity to avoid any overload problems. When the system is turned on, there is an initial peak current that can compromise the source if it is too close to the full capacity. Leave a 20% capacity tolerance.

For a CCTV project, it is necessary to know which current (amperage) each camera consumes, so you can use the appropriate power supply. This information is on the camera label or in the installation manual, in some cases, instead of the current, we find the power information in W (watts), so just do the conversion through a simple division calculation. Below is an example of a camera that shows the power in Watts and the voltage (V), from there we can calculate which is the current that will be used.
Now that we know how much current is needed for one camera, do the same for the rest of the equipment and add up the total of cameras that will be used in the project to calculate the necessary power supply, and keep in mind to use 80% of the capacity.

Choosing the correct power supply for a group of CCTV cameras

Let’s suppose we have 16 cameras that will be installed in a DVR and assuming that the source will be used only for the cameras since the recorder has its separate. Here are the calculations that need to be done:
16 camera at 0.35A (350mA) each: ​16 x 0.35 = 5,6A
Considering the maximum 80% capacity: 5,6 / 0,80 = 7A

So it’s necessary to have a 7A power supply for a 16 CCTV cameras project. With a 7A power supply, we can connect the cameras as shown in the image below
Repeat the process for the other cameras, splitting between the other connectors that have not yet been used. In the example above there would be 8 cameras in each pair of connectors (V- V+). In practice, it is best to buy a power supply that has more connectors available to make the installation easier and organized. There are other professional power supplies that allow the connection of each camera to its own fuse-protected and LED post that indicates if the camera is powered. See the example in the image below:
This is a centralized 12VDC and 10A power supply with individual terminals for connecting up to 18 cameras. The fuses are PTC type that opens as there is a high current that heats the circuit and closes when it ceases the passage of the current, so it resets itself without needing to be replaced. A power supply like this allows the connection of 18 cameras with a maximum consumption of 500mA each. (10/18 = 0.55). That would be enough for our previous example with 16 cameras that consume 350mA each.
Quick calculations: 16 cameras x 350mA –> Calculation: 16 x 0.35 = 5,6A
80% maximum power supply usage –> Calculation: 6,3 / 0,80 = 7A

The image below shows the installation of 16 cameras using a power supply that allows connecting each one individually.
Good quality power supplies allow voltage variation to compensate for cable losses or high voltage that can reach the camera
A good CCTV camera can work with a 10% variation in power, so we can use a potentiometer like the one shown in the picture to vary the voltage for more or less voltage. With a variation of 10% down, we have the voltage at 10.8V and with a variation of 10% up we have the voltage at 13.2V. Both are enough. Here’s a list of CCTV power supplies that you can take a look. Do your calculations and make sure it handles all your camera (and leave 20% capacity tolerance). We recommend to read this article as well: Best coaxial cable for HD analog CCTV.