In recent years, the development momentum of PoE power supply technology has become stronger and stronger. With a series of advantages such as simplified installation and deployment of electrical equipment, energy saving, and safety, PoE power supply has become the new favorite of wireless coverage, security monitoring, and smart grid scenarios. In technical exchanges, one of the most perplexed by engineering companies is the problem of POE power supply. This article summarizes the most concerned questions and focuses on answers.
Question 1: What is PoE technology?
PoE (Power Over Ethernet) refers to some IP-based terminals (such as IP phones, wireless LAN access points AP, network cameras without any changes to the existing Ethernet Cat.5 cabling infrastructure). Etc.) While transmitting data, it can also provide DC power supply technology for such devices. PoE technology can ensure the normal operation of the existing network while ensuring the safety of the existing structured cabling, minimizing costs.
A complete PoE system includes two parts: the power supply device and the power receiving device.
Power Supply End Equipment (PSE): Ethernet switches, routers, hubs or other network switching equipment that support POE functions.
Power receiving device (PD): In the surveillance system, it is mainly a network camera (IPC)
Question 2: How to choose a PoE switch?
1. How much power consumption equipment needs to be powered: PoE switches adopt different standards, and the output power will be different. For example: IEEE802.3af does not exceed 15.4W, and due to the loss of transmission wire, the maximum power consumption can not exceed 12.95W Powered by the device. PoE switches that comply with the IEEE802.3at standard can supply power to devices with a maximum power consumption of no more than 25W.
2. How many devices can be powered at most: An important indicator of a PoE switch is the total power of PoE power supply. Under the IEEE802.3af standard, if the total PoE power supply of a 24-port PoE switch reaches 370W, it can supply 24 ports (370/15.4=24), but if it is a single port according to the IEEE802.3at standard, the maximum When the power supply is 30W, it can only supply power to 12 ports at the same time (370/30=12).
3. The number of interfaces required, whether with optical fiber ports, with or without network management, and speed (10/100/1000M).
Question 3: Is the PoE power supply stable?
From a technical point of view, PoE technology has been developed for many years and is currently in a very mature stage. Standard PoE power supply is stable and safe enough. However, due to the cost pressure of the current monitoring market, the quality of the PoE switches or cables selected is too low, or the solution design itself is unreasonable, the power supply distance is not arranged or too many high-power devices are connected, and the power supply is insufficient (especially night monitoring devices) When heating mode is turned on). Therefore, engineering companies generally hold the view that PoE power supply is unstable.
The network monitoring project is different from the 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 entire system.
Question 4: Does the PoE power supply switch save energy?
As we all know, one of the major advantages of PoE power supply is energy saving, but where does energy saving manifest itself? Take the MS series standard PoE power supply switch as an example to solve the doubt.
The PoE power supply switch will automatically adjust the power according to the power supply equipment. For example, when the temperature of an infrared dome camera is low, the heating function power reaches 30Wmax, and the power is 24W max under normal conditions. The PoE switch will automatically adjust the power supply according to the operating status of the dome camera.
The MS series standard PoE switch can set the PoE power supply cycle. It can automatically stop power supply to the terminal of the designated port during holidays and night time, which not only saves energy, but can also set flexible usage in certain scenarios.
The MS series standard PoE switch will monitor the status of all ports in real time. If the port status is down, the system will automatically stop powering the port and enter the energy-saving mode, which not only saves energy, but also ensures the stable operation of normal equipment.
Question 5: Is the greater the power of the PoE power supply switch, the better?
Due to the emergence of high-power devices such as high-definition dome cameras and real-time video phones, network equipment manufacturers are vying to develop PoE switches with higher total power. However, many products only pursue the improvement of total power, ignoring the relationship between power and the number of ports. When the power is large, the overall cost of the equipment will inevitably increase. As a result, the PoE switches selected by users are not practical and cost-effective. Therefore, in actual deployment, you should first determine the power and number of PD devices, and select the most suitable PoE switch.
Question 6: What are the advantages of PoE power supply solutions?
1. Simplify wiring and save labor costs. A network cable transmits data and power supply at the same time. PoE eliminates the need for expensive power supplies and the time spent installing power supplies, saving costs and time.
2. Safe and convenient The PoE power supply terminal equipment will only supply power to the equipment that needs power supply. Only when the equipment that needs power supply is connected, the Ethernet cable will have voltage, thus eliminating the risk of leakage on the line. Users can safely mix original equipment and PoE equipment on the network, and these equipment can coexist with existing Ethernet cables.
3. Convenient for remote management Like data transmission, PoE can supervise and control the device by using Simple Network Management Protocol (SNMP). This function can provide functions such as shutdown at night and remote restart.
Question 7: What are the risks or disadvantages of PoE power supply technology in engineering applications?
1. Insufficient power, the receiving end can not move: 802.3af standard (PoE) output power is less than 15.4W, which is sufficient for general IPC, but for high-power front-end equipment such as dome cameras, the output power cannot reach To the request.
2. Risk is too concentrated: Generally speaking, a 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 workload of after-sales maintenance. In the sense of safety and stability, independent power supply has the best stability and safety.
Question 8: 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, and it is recommended to use Cat 5e copper network cable.
It is possible to transmit DC power with a standard Ethernet cable for a long distance, 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.
However, there are already some PoE switches that can reach a transmission distance of 250 meters, which is sufficient for long-distance power supply. It is also believed that with the development of PoE power supply technology in the near future, the transmission distance will be extended farther. PoE power supply technology has high requirements for wires. It is recommended that in monitoring projects, you should never save costs on wires. The gains outweigh the losses.
Question 9: Should I buy a non-standard or a standard PoE switch?
Whether it is non-standard or standard, it mainly depends on whether the AP and IP Camera to be powered support 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 power receiving device, you need to find the corresponding 12/24V non-standard power supply switch, or you can buy a standard one. At this time, you need to buy a PD power splitter to convert PoE into DC power supply and network cable data .
Then why it is recommended that everyone buy the standard, because there are many hidden dangers!
The working principle of the non-standard PoE power supply switch is that it belongs to the switching power supply category. There is no PoE chip. It only uses a transformer to step down 220V AC into 48V DC. It does not detect the lower-end power receiving equipment and directly outputs the voltage and current on each RJ45 port without interruption. , May cause the voltage to be too high and burn out the lower-end power receiving equipment. Such a device cannot be directly connected to other network devices, because the direct connection easily causes the two pairs of the network cable in the PoE power supply to form a short circuit. The port is damaged, and the smoke and fire are likely to cause accidents. .
In summary, the standard PoE power supply switch has a PoE control chip inside, which 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 power supply device with a strong network cable. It is powered as soon as the power is turned on. There is no detection step. It is powered regardless of whether the terminal is a PoE powered device, and it is easy to burn the access device.
Question ten: How to distinguish between standard PoE and non-standard PoE?
1. Look at the specifications, if the output is 12-24V, it must be non-standard.
For example, a certain treasure 8-port 6-port POE power supply switch; but according to the specifications, 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 at a glance. It is not surprising that it is so cheap, because the manufacturer also saves PoE chips in order to save costs. Lost. But if the port outputs 48V, it must be a standard PoE switch? Not necessarily, we have to use the second trick.
2. Use a multimeter to check the corresponding line sequence of 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, touch the power supply pins of the PSE device with the two meter pens of the multimeter (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 measured, it is a non-standard product. Because in this process, PSE does not detect the power receiving device (here, a multimeter), and directly uses 48V or other voltage values to supply power.
Conversely, if the voltage cannot be measured, and the multimeter needle jumps between 2~10V, it is a standard POE. Because at this stage, the PSE is testing the PD end (here, the multimeter), and the multimeter is not a legal PD, the PSE will not supply power and no stable voltage is generated.
If it is a standard PoE power supply device, it will send a very small voltage when supplying power to the device below, first check whether there is a corresponding power receiving device connected below; then provide it according to the power required by the device below The corresponding voltage and current. Although the PoE power supply switch in Figure 2 below is written as 48V output, it is the same as other non-standard PoE switches. It is actually a switching power supply and does not have a PoE chip.
Engineering business friends who have done monitoring and wireless engineering know that the reliability of engineering products is very important; the reliability is low, and the reliability of the entire system is lower, which not only affects the company’s business development, but also adds a huge system to the engineering company Maintenance costs, and some even cannot be accepted, causing serious losses.
Question 11: So as long as it is a standard PoE power supply switch, the reliability must be high and stable?
The reliability of the equipment is closely related to the environment of use. Commercial switches are generally used indoors, and industrial switches are generally used outdoors, and their reliability requirements are different. Here we temporarily use commercial switches as an example. The reliability of a commercial POE switch is mainly composed of two parts, one is the switching part, mainly composed of (PCB, switch chip + PoE chip, other electronic materials), and the other is a built-in and external power supply for POE. Because the power supply is responsible for the entire power supply, its reliability is the most important. problem
Twelve: How to know how many APs and IPCs a PoE power supply switch can use?
For example, a 5-port 100M 4-port PoE power supply switch can be found on the official website and specifications that its PoE maximum output power is 57W. How many network cameras of this pixel can be connected?
You can first go to the official website to find the corresponding power consumption option in its detailed parameter column: 5W MAX (7W when ICR is switched), ICR means night infrared. The maximum output power of the POE/the maximum consumption of the camera is the maximum number of support. 57W/7W is equal to 8. Because there are only 4 POE power ports, only 4 are supported, and the others are similar.
A careful friend may find that, no, you didn't count the loss on the network cable. It is true that the loss on the network cable is mainly the current * the resistance of the network cable, so the worse the quality of the network cable, the greater the loss, so this model we made uses eight-core power supply, 51V output, increased voltage, and eight-core parallel circuit shunt design. Reduce the current transmitted on the network cable to reduce the loss, and at the same time can support more power receiving equipment. Even low-quality network cables can support long-distance transmission and power supply of 250 meters to solve monitoring wiring. Some costly wiring such as extenders and optical fibers need to be deployed over 100 meters.
Question 13: How to choose a PoE switch for security monitoring and wireless coverage?
There are many types of PoE switches, from 100M to Gigabit, and then to full Gigabit. There are also differences between non-network management and network management. The number of different ports is different. If you want to choose a suitable switch, you need a comprehensive consideration. . 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, camera resolution, bit rate, frame number and other parameters need to be selected. Major monitoring equipment manufacturers such as Haikang and Dahua provide professional bandwidth calculation tools. Users can use the tools to calculate the required bandwidth to select a suitable PoE switch.
Step 3: Choose af or at standard PoE switch
Choose according to the power of monitoring equipment. For example, if you use a camera of a well-known brand with a power of 12W max, you need to use an af standard switch in this case. The power of a high-definition dome camera is 30W max. In this case, an at-standard switch is required.
Step 4: Select the number of ports on the switch
PoE switches can be divided into 4 ports, 8 ports, 16 ports, and 24 ports according to the number of ports, which can comprehensively monitor the power, quantity, location, power supply and price of the switch.