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How much do you konw about POE ?

1.What is POE?

POE (Power Over Ethernet) is short for active Ethernet Power supply, referring to the existing Ethernet Cat. 5 cabling infrastructure do not make any changes in circumstances, for some based on IP terminal (e.g., IP telephone, wireless LAN access point AP, webcams, etc.) to transmit data signals at the same time, also can provide such equipment with technology of dc Power supply.POE technology can ensure the security of the existing structured wiring while ensuring the normal operation of the existing network, thus minimizing the cost.

2.POE power supply standard

To see how many cameras can be powered by a PoE switch at the same time, consider two aspects: the power standard of the PoE switch and the total power of the PoE switch.

The power supply of the PoE switch can be understood as the single-port power supply of the PoE switch.The popular PoE switches on the market come with two standards, IEEE802.3af and IEEE802.3at.Power supply power is defined as 15.4w in the IEEE802.3af standard, and up to 30W in the IEEE802.3at standard.For example, if the camera power is 9W, you can use the af standard PoE switch.If the camera power is 20W, use at standard PoE switch;If the camera power is more than 30W, the special PoE power supply module is needed to power the camera.

Af standard 802.3:

Supply voltage: 44-57v

Power supply current: 10 ~ 350mA

Maximum power supply: 15.4W

Maximum electric power: 12.95W

At standard 802.3:

Supply voltage: 50-57v

Power supply current: 10 ~ 600mA

Maximum power supply: 30W

Maximum electrical power: 25.5W

In general, a PoE switch that supports both af and at power standards is self-adaptive.For example, if it's connected to a 5W device, then it provides 5W power;If the connection is a 20W device, then provide 20W power.

3.POE power supply process

1) detection

Before power supply, the power supplier will output a small voltage to detect whether the PoE is supported by the electrical equipment. If not, the power is not supplied.If supported, proceed to the next step.

2) classification

After determining the PoE support from the receiving party, the power supplier will conduct further testing to determine the power required by the receiving party and classify the receiving party.

3) start power supply

4. Total power of POE switch

The total power of the PoE switch is a very important indicator of how many cameras you can bring.In the case of a PoE switch with a power supply of 400W and 24 ports, the total power of the PoE switch after the loss is about 370W.

Under the IEEE802.3af standard, it can supply 24 ports full (370/15.4=24), which means it can supply power to 24 cameras at the same time, i.e. full load.However, if the power is calculated as 30W of single port maximum power according to IEEE802.3at standard, at the same time the power can only be supplied to 12 ports (370/30=12).

In actual use, the maximum power consumption of many ordinary webcams is low, which is basically no more than 15W. If the power of each PoE port is reserved according to the maximum power (such as 30W), some port PoE power will not be used up, while some ports cannot be separated from the power.For example, some PoE switches support dynamic power distribution to avoid this situation.When choosing a PoE switch, see if the switch supports dynamic power distribution, so that each port allocates only the actual power used, making more efficient use of the PoE switch's power supply.

5. Technical advantages of POE

1) simplify wiring and save costs

Many live devices, such as surveillance cameras, need to be installed where AC power is difficult to deploy, and POE saves money and time by eliminating the need for expensive power and the time it takes to install it.

2) convenient remote management

Like data transmission, POE can monitor and control the device by using the simple network management protocol (SNMP).This function can provide such functions as night shutdown, remote restart, and so on.

3) safe and reliable

POE power supply terminal equipment only supplies power to the equipment that needs power supply. Only when connected to the equipment that needs power supply, Ethernet cable will have voltage, thus eliminating the risk of power leakage on the line.Users can safely mix legacy and POE devices on the network that can coexist with existing Ethernet cables.


Contact: cherry

Phone: 18948217138

Tel: 0752-3838471

Email: cherry@szsanyi.cn

Add: #Yingfeng Industrial park, Economical and developing Zone, Sanhe, Huiyang, Huizhou , Guangdong Province, China

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