About the advantages and disadvantages of Poe Power

Source: Internet
Author: User

Security engineers must know the truth about Poe powering


1Does Poe Supply stable?

With the rapid development of network monitoring in recent years, the technical threshold is also more and more high, the technical support provided by manufacturers is becoming more and more comprehensive and systematic. Tom is a small security June, has been soaked in security market sales for many years, every day with the engineering business friends to deal with. In the technical exchange, the most puzzled by the problem of Poe power supply, Tom deeply Poe is important to the engineering, for this, Tom invited a Poe technical experts, focused on the issue of doubts.

  Question one: What is Poe technology?

PoE (Power over Ethernet) refers to the existing Ethernet CAT.5 cabling infrastructure without any changes, while for some IP-based terminals (such as IP telephones, wireless LAN access point APS, network cameras, etc.) while transmitting data, It can also provide DC-powered technology for such devices. Poe Technology can ensure the safety of existing structured cabling while ensuring the normal operation of the existing network, minimizing costs.

A complete Poe system consists of two parts: a power supply terminal device (pse,power Sourcing equipment) and an electrical end device (pd,powered device).

Power-Supply Device (PSE): POE-enabled Ethernet switches, routers, hubs, or other network switching devices

Electrical End Device (PD): The main Network Camera (IPC) in the monitoring system

  Question two: Does Poe supply stabilize?

From a technical point of view, Poe's technology has been developing for many years and is now in a very mature stage. However, due to the current monitoring market under the pressure of cost, the choice of Poe switch or wire quality is too poor, or the design itself is unreasonable, resulting in the use of Poe-powered project maintenance of a particularly large workload, so there is a widespread engineering vendor Poe power supply instability.

Network monitoring project, different from the general network cabling, data transmission is very large, high power, and requires all-weather uninterrupted work, the use of quality assurance of Poe equipment and wire is the stability of the entire system guarantee.

  Question three: What are the advantages of the Poe power scheme?

1. Simplify cabling and save labor costs

A network cable transmits both data and power, and Poe eliminates the need for expensive power supplies and the time it takes to install power, saving money and time.

2. Safe and Convenient

Poe Power-supply devices will only power the equipment needed to power, only connected to the power supply equipment, Ethernet cable will have a 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 Remote Management

Like data transfer, Poe can monitor and control the device by using Simple Network Management Protocol (SNMP). This feature can provide functions such as night shutdown, remote restart, and so on.

2Poe power supply technology risk or disadvantage

  Question four: What are the risks or disadvantages of Poe power supply technology in engineering applications?

1. Insufficient power, the end of the power is not moving: 802.3AF standard (PoE) output power is less than 15.4W, for the general IPC is sufficient, but for the ball machine and other high-power front-end equipment, the output power is not up to the requirements.

2. Risk is too concentrated: In general, a Poe switch will power multiple front-end IPC, and any failure of the switch's Poe power supply module will cause all cameras to be out of work and risk being too concentrated.

3. High equipment and maintenance costs: compared to other power supply methods, Poe power supply technology will increase the after-sales maintenance workload, from the sense of safety and stability, the stability of the individual power supply, the best security.

 Question five: How do I choose a poe switch?

1. How much power consumption needs to be powered: Poe switches use different standards, output power will be different, such as: IEEE802.3AF maximum not more than 15.4W, due to the loss of transmission wire, can give maximum power consumption of not more than 12.95W equipment power. A POE switch that complies with the IEEE802.3AT standard provides power to devices with a maximum power consumption of less than 25W.

2. How many devices can be powered up: An important indicator of Poe switches is the total power of Poe power. Under the IEEE802.3AF standard, if the total Poe power of a 24-port Poe switch reaches 370W, it can be up to 24 ports (370/15.4=24), However, if it is based on the IEEE802.3AT standard single-port maximum power 30W calculation, at the same time only 12 ports can be powered (370/30=12).

3. The number of interfaces required, whether with fiber port, with no network management, rate (10/100/1000m).

  Question six: the safe transmission distance of Poe power supply? What are the suggestions for selecting a network cable?

The safe transmission distance of Poe Power is 100 meters, it is recommended to use Super Five type full copper cable.

Poe Power Cable Requirements This problem is only a problem in countries such as China, where fake bargains are rampant, and in many developed countries it is not a problem. POE IEEE 802.3AF Standard requires that the output power of the PSE output port is 15.4W or 15.5W, the transmission of 100 meters after the PD device acceptance power must be no less than 12.95W, according to the 802.3AF typical current value of 350ma, 100 meters network resistor must be ( 15.4-12.95w)/350ma = 7 ohms or (15.5-12.95)/350ma = 7.29 ohms.

While the standard cable is natural to meet this requirement, the IEEE 802.3AF Poe power supply standard itself is measured by a standard cable. And only so will produce Poe power cable requirements This problem, is because many network cables are non-standard network cable, not strictly according to the requirements of the standard cable production. The market's non-standard cable material is mainly copper clad steel, copper clad aluminum, copper nanocrystals, and so on, these network cable resistance is large, are not suitable for Poe power supply. Poe must be powered using an oxygen-free copper cable, or standard cable.

Poe power supply technology to the high demand for wire, it is recommended in the monitoring project, do not save costs on the wire, not worth the candle.

Control of damage risk of DC power supply/poe in key security system
———— High Reliability Intelligent Dual backup security dedicated power supply
At present, most of the security monitoring system front-end cameras and other equipment power supply, almost all using DC 12V single small power mode. Although the cost is low, but from the reliability, stability, normative, there are many hidden dangers. Small power supply are not do lightning grounding, those plastic shell of small power can not be grounded, heat dissipation is also very poor, while many small power accumulation in the cabinet appears very messy. This mode of power supply can not guarantee the reliability and stability of the system, nor can it realize the standardization of system integration.
At present, there are some network cameras using Poe power supply mode, because this mode by the network cable diameter constraints, the use of DC 48V power supply, the fact is the front-end cameras and other security equipment, the general power supply is DC 12V, which is unavoidable in the front-end equipment must be high-voltage 48V to normal 12V to be used by the device. Such a large pressure drop will inevitably in the camera and other security equipment tight crowded interior space to generate a lot of heat, so whether the normal use of equipment or equipment life is a great negative impact, and these should be in the design phase need to avoid!
The current security system adopted the mainstream camera for network cameras, are built-in intercom, broadcast, alarm and so on hanging interface, the use is very convenient. If the network camera is powered by Poe, it seems to save the installation of a separate power cord. But the network camera itself did not give the hanging of the intercom, broadcast, alarm and other equipment to power supply, the reason is precisely the large pressure difference of buck produced by the calorific value of the network camera itself can not bear! As a result, there is still a need to separate the intercom, broadcast, alarm and other equipment to lay power lines, then the use of Poe mode power supply is to save investment, or illusory it?
Poe powered switch or Poe power supply, typically powering several or dozens of cameras, but the internal is just a shunt power supply, and there is no power failure redundancy function. Once Poe power failure can cause a wide range of camera downtime, especially in the key security system should be avoided and not allowed to appear! To do this only by the traditional single small power supply, Poe power supply mode is absolutely impossible, it is to comply with the actual strong demand of this market only to appear "high-reliable intelligent dual backup security dedicated power supply."

First, the technology is immature, the industry application plane is narrow, prone to malfunction.

At home,


The technology is only in the corridor switch of the resident network has less application, in the industry application

The high reliability of the network is largely not applied. From


The standard was established, however, the standard

Shortcomings have been restricting the expansion of the market. Until




Month, this standard was allowed, lasted very

Long, not widely used in China until now.

Second, the equipment power supply instability, resulting in the city center of the network paralysis.


May cause the entire network to be paralyzed. If


The module is broken, then the entire network is powered

It's going to be paralyzed. This is a serious accident for any network!


Low device stability. Compared to mainstream module applications, this module has a large output power and

The overall equipment power requirement is very high, then the overall stability of the equipment will be reduced.



The power connector is prone to aging.

The reason is


Power supply is used



And this kind of plastic material expansion and contraction degree is also more serious, durability is not high.



Module failure rate is high. Because


Requires a separate configuration module, from a variety of network settings

Experience, the failure rate of the modular product is the highest failure rate in the network product

The high part, the maintenance is inconvenient.

Third, the use


Power supply, indirectly increases the cost of network construction.


The modules need to be configured separately.

Since the reliability of this module is not high,

To configure a redundant power supply,

And redundant power supply is to high performance, increase the cost of network construction.


In this kind of environment with traditional power supply center room,

Use this


Mode of power supply

Not very suitable,

This power supply method is only suitable for the corridor,

Power shortage,

Equipment reliability requirements are not high

Use in your environment.

About the advantages and disadvantages of Poe Power

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