Explore video monitoring several power supply methods

Many people have doubts about the power supply for video surveillance. They do not know how to choose the right power supply method. Xue Ge summarized some of this knowledge and hopes to help everyone!

There are three kinds of power supply methods for video surveillance, which are point-to-point power supply, centralized power supply, and PoE power supply. Let's take a look at their respective advantages and disadvantages.

First, point to point power supply

Point-to-point power supply refers to direct 220V AC power from the monitoring room and DC12V or AC24 power supply next to the camera.

Advantages: 220V AC voltage loss during transmission, strong anti-interference ability.

Disadvantages: Each point must be installed a power supply, construction is more troublesome.

Second, centralized power supply

The centralized power supply mode refers to centralized power supply to the front-end load using a 12V switching power supply in the monitoring room or an intermediate point.

Advantages: Convenient construction, easy maintenance, saving power costs

Disadvantages: DC low-voltage power transmission distance is too long, high voltage loss, poor anti-interference ability in the transmission process, easy to cause front-end camera voltage instability, less than 12V, etc.

Third, PoE power supply

PoE power refers to the technology that provides DC power to other devices without any changes to the existing Ethernet cabling infrastructure. This method is mainly used in high-definition network digital surveillance systems or wireless AP networks.

Advantages: Cost reduction, flexible deployment, and maximum single port power up to 30W.

Disadvantages: High quality requirements on the network cable, limited transmission distance.

Precautions:

When using infrared cameras, centralized power supply is not recommended. Because the current is larger when the infrared is turned on, it is difficult to ensure that the infrared effect of all cameras is best when the centralized power supply mode is used. Point-to-point power supply is sometimes cumbersome to construct, and it is necessary to find a suitable power supply point. PoE power supply is now used more often. Most of them are powered by PoE switch or power supply, which can save labor costs.

The following focuses on the application of POE power supply in video surveillance

Many people who have just come into contact with PoE switches do not know how many surveillance cameras are connected to a PoE switch.

To understand how many cameras a PoE switch can connect at the same time, look at three aspects: the PoE switch power supply standard, the total power supply of the PoE switch, and the video stream of the camera.

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1, PoE switch power supply standard

The popular PoE switches in the market have two standards, IEEE802.3af and IEEE802.3 at, which define the power supply of 15.4W and 30W, respectively. However, due to the loss in the transmission process, the actual power supply is 12.95W and 25W.

When using a PoE switch that supports the IEEE 802.3af standard, the power of the powered device cannot exceed 12.95 W. Similarly, when using a PoE switch that complies with the IEEE 802.3at standard, the power of the powered device cannot exceed 25 W.

In general, a PoE switch that supports the IEEE802.3af/at standard at the same time, the power supply is adaptive. For example, it is connected to a 5W device and then provides 5W of power; if a 20W device is connected, then 20W of power is provided.

2, The total power of the PoE switch

This can be judged from the total power of the PoE switch. Under the IEEE802.3af standard, if the PoE power supply of a 24-port PoE switch reaches 370 W, then it can supply 24 ports (370/15.4=24), but if it is the maximum number of ports according to the IEEE802.3at standard The power supply is calculated at 30W, and at most 12 ports can be powered at the same time (370/30=12).

For example, an 8-port PoE switch supports IEEE802.3af/at standard. The power of a single camera is 11W. Then the switch can connect 8 such cameras; if the power of a single camera is 20W, one or two ports are reserved. Good, it is recommended to connect 5-6 cameras.

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3, the camera stream

If simply looking at the power supply of a PoE switch is inaccurate, network monitoring requires high definition and smoothness. Therefore, according to the video stream of the camera, after all, the PoE switch is not only powered but also transmits video data.

The video stream of commonly used cameras: 720P (1 million pixels) stream is 4.5M, 960P (1.3 million pixels) stream is 6M, 1080P (2 million pixels) stream is 8M, 3 million pixel stream is 10M, 500 The megapixel stream is 13-15M.

When transmitting video data, the actual bandwidth utilization of PoE switches is only about 60%.

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For example, for an 8-port PoE switch, the port transmission rate is 100Mbps. The camera is 720P. How many such cameras can be connected?

The camera stream of the 720P is 4.5M. The available bandwidth of this PoE switch is about 60Mbps and about 60/4.5. Because the PoE switch has only 8 PoE power ports, it can be fully loaded.

Similarly, if this 8-port 100M PoE switch is connected to a 1080P camera, then only up to 7 such cameras can be connected.

In the actual use of PoE switches, it is necessary to consider the power supply, but also to consider the camera code stream, must be satisfied both, will be used to ensure smooth security.