Detailed knowledge of POE power supply
With the rapid development of IP telephones, wireless LAN access point APs, and 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. Among the technical exchanges, among the most confused by engineering companies is the problem of POE power supply.
Question 1: What is PoE technology?
PoE (Power Over Ethernet) refers to the existing Ethernet Cat.5 cabling infrastructure without any changes, for some IP-based terminals (such as IP phones, wireless LAN access point AP, network cameras Etc.) While transmitting data, it can also provide DC power supply technology for such devices. PoE technology can ensure the safety of the existing structured cabling while ensuring the normal operation of the existing network, greatly reducing costs.
A complete PoE system includes two parts: power supply equipment (PSE, Power Sourcing Equipment) and power receiving equipment (PD, Powered Device).
Power Supply Equipment (PSE): Ethernet switches, routers, hubs, or other network switching equipment that support POE
Power receiving device (PD): The wireless coverage project is mainly wireless AP.
Question 2: Is the PoE power supply stable?
From a technical point of view, PoE technology has developed over the years and is now in a very mature stage. However, due to the current cost pressure of the monitoring market, the quality of PoE switches or cables used is too low, or the scheme design itself is unreasonable, resulting in a particularly heavy workload for projects using PoE power supply. Stable view.
In the case of very large data transmission, high power, and the requirement for 24/7 uninterrupted work, the use of quality-assured PoE equipment and wires is a guarantee for the stability of the entire system.
Question 3: What are the advantages of PoE power supply solutions?
1. Simplify wiring and save labor costs
A network cable transmits data and power at the same time. PoE eliminates the need for expensive power supplies and the time it takes to install power supplies, saving costs and time.
2. Safe and convenient
PoE power supply equipment will only supply power to the equipment that needs to be powered. Only when the equipment that needs to be powered is connected, there will be voltage on the Ethernet cable, thus eliminating the risk of leakage on the line. Users can safely mix original devices and PoE devices on the network, and these devices can coexist with existing Ethernet cables.
3. Facilitate remote management
Like data transmission, PoE can monitor and control the device by using Simple Network Management Protocol (SNMP). This function can provide functions such as night shutdown and remote restart.
Question 4: What are the risks or disadvantages of PoE power supply technology in engineering applications?
1. Insufficient power, the power receiving end cannot be driven: 802.3af standard (PoE) output power is 15.4W. For high-power front-end equipment, the output power cannot meet the requirements.
2. Risk is too concentrated: Generally speaking, a PoE switch will supply power to multiple APs at the same time. Any failure of the POE power supply module of the switch will cause all equipment to fail to work, and the risk is too concentrated.
3. High equipment and maintenance costs: Compared with other power supply methods, PoE power supply technology will increase the after-sales maintenance workload. In the sense of safety and stability, the stability and safety of separate power supply are very good.
Question 5: How to choose a PoE switch?
1. How much power is required to power the equipment: PoE switches use different standards, and the output power will be different, for example: IEEE802.3af does not exceed 15.4W, due to the loss of transmission wires, can provide equipment with power consumption not exceeding 12.95W powered by. PoE switches that comply with the IEEE802.3at standard can provide power to devices with power consumption not exceeding 25W.
2. How many devices can be powered: An important indicator of PoE switches is the total power of PoE power supply. Under the IEEE802.3af standard, if the total PoE power 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 power supply according to the IEEE802.3at standard The power is calculated at 30W, and at the same time, it can only supply power to 12 ports at most (370/30 = 12).
3. Need the number of interfaces, whether to bring fiber port, with or without network management, speed (10/100 / 1000M).
Question 6: The safe transmission distance of PoE power supply? What are the suggestions for the selection of network cables?
The safe transmission distance of POE power supply is 100 meters. It is recommended to use all five types of copper cables.
The POE power supply network cable requires this problem to be a problem only in countries such as China and other countries where fake goods and cheap goods are rampant. 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 is 15.4W or 15.5W. The PD device receiving power after transmitting 100 meters must be not less than 12.95W. According to the 802.3af typical current value of 350ma, the resistance of the 100 meter network cable must It is (15.4-12.95W) / 350ma = 7 ohms or (15.5-12.95) / 350ma = 7.29 ohms.
The standard network cable naturally meets this requirement. The IEEE 802.3af poe power supply standard itself is measured with a standard network cable. The reason why POE power supply network cable requirements arise is because many network cables on the market are non-standard network cables, which are not produced in strict accordance with the requirements of standard network cables. The materials of non-standard network cables on the market mainly include copper-clad steel, copper-clad aluminum, and copper-clad iron. These network cables have large resistance values and are not suitable for POE power supply. POE power supply must use oxygen-free copper network cable, that is, standard network cable.