Weak Electrical Engineering POE Switch Usage Guide

The POE switch is a Power over Ethernet switch that provides the DC power required by the network terminal equipment through the existing Ethernet twisted pair cable without changing the original network architecture. Power is usually supplied to PoE terminal devices such as wireless APs, webcams, and handheld computers.

Classification of POE switches

1. Standard POE switch

Compliant with IEEE802.3af and 802.3at standards, it is a standard POE switch (commonly known as 48V). The complete POE includes two parts: power supply equipment (PSE, Power Sourcing Equipment) and power receiving equipment (PD, Power Device). POE switch is PSE. A type of device. The PSE is a device that powers the terminal and is also the administrator of the POE Power over Ethernet process. The PD is a terminal device that receives power supply (the 48V GB device contains a PD chip).

2. Two types of non-standard POE switches

Conversely, non-standard POE switches ("non-standard" abbreviated as "non-standard" commonly known as 24V, but not labeled 48V, 24V, 12V, 5V, etc.). There is no POE control chip inside the non-standard POE power supply. It directly transmits power through the empty line pair 45, 78 in the network cable. It does not detect this step. It will force it to be powered regardless of whether the IP terminal supports POE. If the IP terminal does not have POE power, it is likely to burn the network port.

Therefore, when purchasing a POE switch, you need to first consult the type of the POE switch, the port output power, the total power of the POE switch, and the backplane bandwidth.

Standard POE power switch working process

1. Detection: The POE switch first outputs a small voltage, and detects a power receiving device (supporting the IEEE802.3at/af standard chip abbreviation "PD") that supports the IEEE802.3at/af standard chip.

2. PD classification: After detecting the PD, the POE switch classifies the PD device and evaluates the power of the PD device.

3. Power supply: During the startup period (generally less than 15μs), the POE switch supplies power from the low voltage to the PD until the voltage required for the PD is supplied, providing stable and reliable DC power for the PD device.

4. Power off: If the PD device is disconnected, the POE switch will stop powering the PD quickly (usually within 300 to 400 ms) and repeat the detection process to detect whether the terminal of the cable is connected to the PD device.

Anti-counterfeiting guide for POE switches

1, don't be cheap

China is a big market for a variety of products, and PoE switches are no exception. There are so many brands of PoE switches on the market, and the price and quality are very different. Some people who are initially exposed to PoE power supply think that as long as they are PoE switches, it doesn't matter if they are broken. Therefore, in order to save costs, it is often the lowest price compared with N.

It's not that it's cheap, it's cheap, there are good goods, but after all, it's less. Generally speaking, the higher the price of a thing, the hardware, parts, accessories, chips, etc. used are high-quality, guaranteed, and very low-priced things, there are many hidden dangers and deficiencies. For PoE switches, the price is too low, and there may be many problems in the later use, such as unstable power supply, no power supply, and inability to perform after sales.

2, try to stay away from non-standard

Most of the PoE switches are standard and some are non-standard. The reason why non-standards exist is because the cost is low, but because some places use non-standards. However, non-standard PoE switches have security risks, such as burning out network devices connected to them. When using a non-standard PoE switch, the supply voltage and the voltage of the powered device must be the same.

The standard PoE switch is safer and can automatically connect to the network device connected to it. Only the PoE switch that supports PoE power supply will start to supply power and ensure the security of the powered device.

3, using the universal meter test

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.

POE Switch Usage Guide

The power supply of the POE switch is equivalent to a power cable. It supplies power to wireless APs and network cameras through the network cable. It not only effectively solves the power supply problem of distance limitation, but also implements centralized management of downlink devices. Although this method is very simple, but the real choice and use, I am afraid it is not so simple, so what should users pay attention to while using the POE switch to power the device?

1, choose the right model

There are many PoE switch models, the number of ports is 4, 8, 16, 24, the port transmission rate is 100 megabits and gigabits, and the power supply is 60W, 150W, 250W, 400W. What port number and port transmission rate are required? All need to choose the right one.

The port transmission rate usage of a PoE switch is about 40~60%. If a network uses a 100M PoE switch in theory, then choose a Gigabit switch. In addition, for surveillance cameras with infrared lamps, the power of the infrared lamps must be considered.

2. Use the best network cable.

The quality of the network cable is critical to the success of the PoE power supply. It is recommended to use five types of network cables, five types of network cables, and six types of network cables. The internal material of the network cable is also very important. Do not use any aluminum wire, copper clad aluminum wire, copper clad iron wire, iron core wire, etc. It is most ideal to use pure copper wire.

3. To be within a reasonable distance of use

In theory, PoE power supply distance is 100 meters, but in view of the quality of the market access line and the environment, the actual power supply distance is kept within 100 meters.

POE switch common problems and solutions

With the use of network cameras more and more widely, the installation and use requirements of different places are different, and the network cameras that supply PoE power are no strangers. PoE power supply only needs to install a network cable for the engineering company, and there is no need to go to the power socket everywhere.

However, in fact, the material selection is not good, and the fault will continue to appear. Therefore, you must understand the POE camera line maintenance method. When testing the voltage, you must carry the load. If you pull out the camera and test the voltage, it is not advisable. It is the voltage of 10,000 meters will not be reduced, please remember that the voltage formula V (voltage) = I (current) * R (resistance), power W = V * I, the two formulas are very useful, can read Knowing this truth will naturally know why it is okay to remove the voltage from the load.

Test the power supply voltage is normal, the current is generated when the machine is installed, the current will produce a voltage drop on the line after the current is generated. The larger the current, the larger the voltage drop, the higher the final product current will cause the product to over-current damage, so sometimes The product does not have to be damaged by high voltage, and the overcurrent will also cause serious damage to the product.

The network camera does not produce images. The problem may be as follows:

1. The cable routing is too long or the internal resistance of the cable is too large (use less than 5 cables).

2, POE output power is not big enough (general gun type infrared network cable camera power is about 3-8W)

3, the network cable wiring sequence is not correct, the correct network cable position is the crystal head contact facing yourself, the network cable is down, the network cable sequence from left to right orange white, orange, green white, blue, blue white, green, brown white, Brown, the above is just a fault caused by the line. In fact, if there is an improper setting, there will be no image.