You need to know the 6 truths about POE power supply.

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With the rapid development of network monitoring in recent years, the technical threshold is getting higher and higher, and the technical support provided by manufacturers is becoming more and more comprehensive and systematic. In the technical exchanges, there are problems with the POE power supply among the engineering companies, so a PoE technical expert was invited to focus on solving problems.


Question 1: What is PoE technology?
PoE (Power Over Ethernet) refers to some IP-based terminals (such as IP phones, WLAN access points APs, network cameras) without any changes to the existing Ethernet Cat.5 cabling infrastructure. While transmitting data, it can also provide DC power supply technology for such devices. PoE technology can ensure the normal operation of existing networks and reduce costs while ensuring the security of existing structured cabling.
A complete PoE system includes two parts: a Power Sourcing Equipment (PSE) and a Powered Device (PD).
Power Supply Equipment (PSE): An Ethernet switch, router, hub, or other network switching device that supports POE.
Receiving device (PD): In the monitoring system, it is mainly the network camera (IPC).
Question 2: Is PoE power supply stable?
From a technical point of view, PoE technology has been developed for many years and is now in a very mature stage. However, due to the cost pressure of the current monitoring market, the quality of the selected PoE switch or wire is too inferior, or the design of the solution itself is unreasonable, resulting in a particularly large workload for the maintenance of the project using PoE power supply. Therefore, the PoE power supply is generally not available to the engineering company. A stable view.
The network monitoring project is different from the common network integrated wiring. The data transmission volume is very large, the power is high, and it requires 24/7 uninterrupted work. The use of high-quality PoE equipment and wires is the guarantee of the stability of the whole system.
Question 3: What are the advantages of the PoE power supply solution?
1. Simplify wiring and save labor costs
A network cable transmits data and power simultaneously. PoE saves time and money by eliminating the need for expensive power and time to install the power supply.
2. Safe and convenient
The PoE power supply device only supplies power to the devices that need to be powered. Only when the device that needs to be powered is connected, the Ethernet cable will have voltage, thus eliminating the risk of leakage on the line. Users can safely mix legacy and PoE devices on the network, which can coexist with existing Ethernet cables.
3. Easy to manage remotely
Like data transmission, PoE can supervise and control the device by using Simple Network Management Protocol (SNMP). This feature provides features such as night shutdown and remote reboot.


Question 4: What are the risks or disadvantages of PoE power supply technology in engineering applications?
1. Insufficient power, the power receiving terminal does not move: 802.3af standard (PoE) output power is less than 15.4W, which is enough for general IPC, but for high-power front-end equipment such as ball machines, the output power is not up to To the request.
2. The risk is too concentrated: Generally speaking, one PoE switch will supply power to multiple front-end IPCs at the same time. Any failure of the POE power supply module of the switch will cause all cameras to fail to work, and the risk is too concentrated.
3. High equipment and maintenance cost: Compared with other power supply methods, PoE power supply technology will increase the after-sales maintenance workload. In terms of security and stability, the stability and security of the separate power supply are good.
Question 5: How to choose a PoE switch?
1. It is necessary to supply power to devices with large power consumption: PoE switches use different standards and different output powers. For example, IEEE802.3af does not exceed 15.4W. Because of the loss of transmission wires, devices that can consume less than 12.95W can be used. powered by. A PoE switch that complies with the IEEE802.3at standard can supply power to devices that consume less than 25W.
2. How many devices can be powered: An important indicator of a PoE switch is the total power of the PoE. Under the IEEE802.3af standard, if the total power of a PoE power supply of a 24-port PoE switch reaches 370W, then it can supply 24 ports (370/15.4=24), but if it is a single port according to the IEEE802.3at standard, the maximum is The power supply is calculated at 30W, and only 12 ports can be powered (370/30=12).
3. The number of interfaces required, whether with fiber ports, with no network management, and rate (10/100/1000M).
Question 6: The safe transmission distance of PoE power supply? What are the suggestions for the selection of network cable?
The safe transmission distance of POE power supply is 100 meters. It is recommended to use super five types of copper cables.
The POE power supply network requires that this problem is only a problem in countries where fake goods such as China are rampant, and it is not a problem in many developed countries. The POE IEEE 802.3af standard requires that the output power of the PSE output port be 15.4W or 15.5W. The PD device receiving power after transmission of 100 meters must be not less than 12.95W. According to the 802.3af typical current value of 350ma, the resistance of the 100m network cable must be (15.4-12.95W) / 350ma = 7 ohms or (15.5-12.95) / 350ma = 7.29 ohms.
The standard network cable meets this requirement. The IEEE 802.3af poe power supply standard itself is measured by standard network cable. However, this problem arises only because the POE power supply network cable is required. This is because many network cables on the market are non-standard network cables, and are not strictly produced according to the requirements of standard network cables. The non-standard network cable materials in the market mainly include copper clad steel, copper clad aluminum, copper clad iron, etc. These cables have large resistance values ​​and are not suitable for POE power supply. The POE power supply must use a network cable made of oxygen-free copper, that is, a standard network cable.
The PoE power supply technology has high requirements on the wire. It is recommended that in the monitoring project, do not save costs on the wire, and it is not worth the candle.

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