In recent years, the development momentum of PoE power supply technology has become stronger and stronger. With a series of advantages such as simplifying the installation and deployment of power equipment, energy saving, and safety, PoE power supply has become the new favorite of wireless coverage, security monitoring, and smart grid.
In the technical exchanges, among the most confused engineers, there is the problem of POE power supply. This article summarizes the issues that people are most concerned about and concentrates on solving them.
Question 1: What is PoE technology?
PoE (Power Over Ethernet) refers to some IP-based terminals (such as IPdian phones, wireless LAN access points APs, network cameras, etc.) 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 while minimizing costs while ensuring the security of existing structured cabling.
A complete PoE system consists of two parts: the power supply device and the power receiving device.
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: 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 at maximum. Due to the loss of transmission wires, the maximum power consumption can be no more than 12.95W. The device is powered. A PoE switch that complies with the IEEE802.3at standard can supply power to devices with a maximum power consumption of less than 25W.
2. How many devices can be powered at most: 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 at the same time, only 12 ports can be powered (370/30=12).
3. The number of interfaces required, whether with fiber ports, with no network management, and speed (10/100/1000M).
Question 3: 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. The standard PoE power supply is stable and safe enough. However, due to the current cost of pressure on the monitoring market, the quality of the selected PoE switch or wire is too low, or the design of the solution itself is unreasonable. The power supply distance is not arranged or the connection of too many high-power devices has caused insufficient power supply (especially nighttime monitoring equipment). When the heating mode is turned on). Therefore, engineering companies generally have the view that PoE power supply is unstable.
The network monitoring project is different from ordinary network integrated wiring. The data transmission volume is very large, the power is high, and it requires 24/7 uninterrupted work. The use of quality-guaranteed PoE equipment and wires is the guarantee of the stability of the whole system.
Question 4: Is the PoE power supply switch energy efficient?
As we all know, the big advantage of PoE power supply is energy saving, but what is the energy saving? Take the MS series standard PoE power supply switch as an example for everyone to doubt.
The PoE power supply switch automatically adjusts the power according to the power supply equipment. For example, when the temperature of a certain infrared ball machine is low, the power of the heating function reaches 30Wmax, and under normal circumstances, the power is 24W max. The PoE switch automatically adjusts the power supply according to the running condition of the ball machine.
The MS series standard PoE switch can set the PoE power supply cycle, and can automatically stop the power supply to the terminal of the designated port during holidays and nights, which not only saves energy, but also can be flexibly used in some scenarios.
The MS series standard PoE switch monitors the status of all ports in real time. If the port status is down, the system automatically stops powering the port and enters the energy-saving mode, which saves energy and ensures stable operation of normal devices.
Question 5: The bigger the power of the PoE power supply switch, the better?
Due to the emergence of high-power devices such as high-definition domes and real-time video dians, network equipment vendors are rushing to develop PoE switches with higher total power. However, many products only pursue the improvement of total power, ignoring the relationship between power and port number. At the same time of high power, the overall cost of the device will be increased. As a result, the PoE switch selected by the user is not practical and has low cost performance.
Therefore, in actual deployment, you should first determine the power and quantity of the PD device and select the most suitable PoE switch.
Question 6: 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 the time it takes 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 devices and PoE devices on the network, which can coexist with existing Ethernet cables.
3, easy to remote management
Like data transmission, PoE can monitor and control the device by using Simple Network Management Protocol (SNMP). This feature provides features such as night shutdown and remote reboot.
Question 7: 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 costs: 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 individual power supply are the strongest.
Question 8: What is the safe transmission distance of PoE power supply? What are the suggestions for the choice 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.
Transmission of DC power with a standard Ethernet cable can be transmitted very far, so why is the transmission distance limited to 100 meters?
The fact is that the maximum transmission distance of a PoE switch mainly depends on the data transmission distance. When the transmission distance exceeds 100 meters, data delay and packet loss may occur. Therefore, the transmission distance should not exceed 100 meters in the actual construction process.
But now there are some PoE switches that can reach a distance of 250 meters to meet long-distance power supply. It is also believed that with the development of PoE power supply technology, the transmission distance will be extended to a long time. 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.
Question 9: In the end, buy a non-standard or standard PoE power supply switch?
Whether it is not standard or standard, this mainly depends on whether the AP, IP Camera to support the power supply supports 48V, 24V or 12V input? If it is 48V, it is written to support IEEE802.3 AT or AF power supply standards, which are generally standard. If it is a 24V and 12V powered device, you need to find the corresponding 12/24V non-standard power supply switch, you can also buy a standard, then you need to buy a PD power splitter, convert PoE into DC power and network cable data .
Then why is it better to buy standard because there are many hidden dangers!
The working principle of the non-standard PoE power supply switch belongs to the switching power supply class. There is no PoE chip. Only a transformer is used to step down the 220V AC power into 48V DC power. The lower end power receiving equipment is not detected, and the voltage and current are continuously outputted directly at each RJ45 port. It may cause the voltage to be too high and burn out the lower end of the powered device. Such a device cannot be directly connected to other network devices, because the direct connection easily causes the network cable 2 in the PoE power supply to be connected to the line, and the positive pole and the negative pole are connected to form a short circuit, and the port is damaged, and the smoke is caught in the fire, which is likely to cause an accident. .
In summary, the standard PoE power supply switch has a PoE control chip inside. It has a detection function before power supply. When the device is connected, the PoE power supply will send a signal to the network to detect whether the terminal in the network supports PoE power supply. PD device. The non-standard PoE product is a strong supply type network cable power supply device. When the power is supplied, there is no detection step. No matter whether the terminal is powered by the PoE power receiving device, it is easy to burn the access device.
Question 10: How to distinguish between standard PoE and non-standard PoE?
1, look at the specifications, if the output is 12-24V, then it is definitely non-standard.
For example, a treasure 8-port 6-port POE power supply switch; but see the specification parameters written, 15V1A output, 19V1A ultra long-distance output. Because the IEEE802.3 AT/AF protocol stipulates that the standard PoE port output voltage range is between 44-57V, so this one knows that it is non-standard, so it is not surprising that it is cheap, because the manufacturer also saves the PoE chip for cost. Lost. But if the port outputs 48V, it must be a standard PoE switch? Not necessarily, we have to use the second move.
2. Use a multimeter to detect the line order corresponding to the port or network cable, and test whether the output voltage is always on the lower network cable.
Start the device, adjust the multimeter to the voltage measurement position, and touch the power supply pin of the PSE device with the two meter pens (usually 1/2, 3/6 or 4/5, 7/8 of the RJ45 port). ), if a device with a stable output of 48V or other voltage values ​​(12V, 24V, etc.) is detected, it is a non-standard product. Because in this process, the PSE does not test the powered device (here, the multimeter) and directly supplies power with 48V or other voltage values.
Conversely, if the voltage is not measured and the multimeter's hands are beating between 2 and 10V, it is a standard POE. Because at this stage, the PSE detects the PD side (here a multimeter), and the multimeter is not a legitimate PD, the PSE does not supply power, and no stable voltage is generated.
If it is a standard PoE power supply device, it will send a small voltage when powering the following devices. First check if there is a corresponding power receiving device underneath; then provide it according to the power required by the following devices. Corresponding voltage and current. Figure 2 below shows that this PoE power supply switch is a 48V output, but like other non-standard PoE switches, it is actually a switching power supply type and no PoE chip.
Engineers who have done monitoring and wireless engineering know that the reliability of engineering products is very important; low reliability, lower reliability of the entire system, which not only affects the company's business development, but also adds a huge system to the engineering company. Maintenance costs, some even fail to accept, causing serious losses.
Question 11: As long as it is a standard PoE power supply switch, the reliability will be high, and it must be stable?
The reliability of the equipment is closely related to the use of the environment. Commercial switches are generally used indoors and industrial switches are generally used outdoors, and their reliability requirements are also different. Here we take the example of a commercial switch. The reliability of commercial POE switches mainly consists of two parts, one is the exchange part, mainly consists of (PCB, switch chip + PoE chip, other electronic materials), and part of it is built-in and external power supply for POE. Because the power supply is responsible for the entire power supply, its reliability is of the utmost importance.
Question 12: How do you know how many APs and IPCs can a PoE power supply switch use?
For example, a 5-port 100-megabit 4-port PoE power supply switch can be found in the specification that its PoE maximum output power is 57W. How many IP cameras can this channel be connected to?
You can first find the corresponding power consumption option in the column of its detailed parameters: 5W MAX (7W when ICR is switched), ICR is the meaning of night infrared.
The maximum output power of the POE/maximum camera consumption is the maximum supported number. 57W/7W is equal to 8 because there are only 4 POE power ports, so only 4 are supported, and others are similar.
Careful friends may find that, wrong, you did not count the loss on the network cable. Indeed, the loss on the network cable is mainly the current * network cable resistance, so the worse the quality of the network cable, the greater the loss, so we used this eight-core power supply, 51V output, improve the voltage, eight-core parallel circuit shunt design, Reduces the current transmitted on the network to reduce losses while supporting more powered devices. Even inferior network cables can support long-distance transmission and power supply of 250 meters, and solve the monitoring wiring. In some cases, more than 100 meters need to deploy costly wiring such as extenders and optical fibers.
Question 13: How to choose a PoE switch for security monitoring and wireless coverage?
There are many types of PoE switches, ranging from 100 Mbps to Gigabit to Gigabit. There are also differences between non-network management and network management. The difference in the number of different ports. To choose the right switch, comprehensive and comprehensive considerations are needed. . Take the project that requires high-definition monitoring as an example.
Step 1: Choose a standard PoE switch
Step 2: Choose a 100M or Gigabit switch
In the actual scheme, the number of integrated cameras, the resolution of the camera, the code rate, and the number of frames are selected. Major monitoring equipment vendors such as Haikang and Dahua provide professional bandwidth computing tools. Users can use tools to calculate the required bandwidth to select the appropriate PoE switch.
Step 3: Select af or at standard PoE switch
According to the monitoring equipment power selection. For example, using a camera of a well-known brand, the power is 12W max. In this case, an af standard switch is required. A high-definition dome machine has a power of 30W max. In this case, an at-standard switch is required.
Step 4: Select the number of ports on the switch
The PoE switch can be divided into four ports, eight ports, sixteen ports, and four ports according to the number of ports. It can comprehensively monitor the power, quantity, location, power supply and price of the switch.
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