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Backup Centralized PoE Power System

The IP device requires not only the data but also the power. We have WiFi, 3G/4G even a 5G connection. However, the cable is still the primary method to provide internet access in a commercial application, such as an IP camera system. The Ethernet cable is made of copper which can transmit the power. It makes sense to take the advantage of copper conduct to send the data as well as the power. This is the Power over Ethernet (POE) technology. There are multiple twisted pairs (4 pairs) of cables in the single Ethernet cable. At the very beginning, only half of the twisted pairs were being used to send the data and the reset twisted pairs were being used to send the power. The fast network (100mbps) only need 2 twisted pair for data. Now the PoE has been evolved these days.

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How does PoE System deal with PoE?

There is one important mechanism in the PoE system – power handshake. In IEEE802.3 POE, the PSE (PoE Switch or PoE injector) has to verify and classify the edge device before sending the power. Technically, the PoE Switch or PoE injector will send a small current and detect the returns. Now the PoE Switch or PoE injector will know whether the edge device is PoE compatible or not. If the edge device is being verified, the PoE Switch or PoE injector will stop releasing the power.

The PoE Switch or injector also needs to classify the edge device. There is PoE/PoE+ and PoE++ (class3/class4). If the edge device is being recognized as PoE (IEEE802.3af), the PoE Switch only will output a maximum of 14.4W even the PoE Switch is PoE++ (class 4) which is capable of outputting 95W. In contrast, if the PoE Switch is PoE (IEEE802.3af) equipment, while it works with the PoE++ edge device, the power system will be set to 14.4W. Only both PoE Switch and edge devices are compatible with PoE ++ (class 4) can build up 95W high power link.

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Power Loss – Can’t skip in PoE system

The maximum output from PoE Switch or PoE injector is not the actual remaining power you will have at the edge. As we know there is always power loss during the transmission, the longer distance, the more power loss will be. The power loss can’t be ignored in the PoE system. The PoE+ system only can guarantee 25.5W even the PoE Switch can output 30W, and the PoE++ only can provide 72W in class 4.

Most of the PoE Switch use sharing power sources. All the PoE ports can take the power from the same power source. However, the power source may not enough to supply all the ports to have maximum output. For example, 16 ports PoE+ port can output a maximum of 30W doesn’t mean you can have all 16 ports with 30W maximum output. If the total power budget of the PoE Switch is 270W, there is no power budget left after you connect 9 PoE IP devices that need full power 30W each. In the practical application, we seldom need full POE output from each of the ports. The PoE access point needs about 3-4W, the VoIP only 5-6W. Some of the infrared IP cameras will take about 10-12W, and the infrared PTZ camera could use 23-25W. We can see there is no need to ask for maximum output for each of the ports. It will be wasting to have 480W 16-channel PoE Switch in this case.

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The new POE standard – PoE++

The PoE++ (IEEE802.3bt) is the latest PoE standard which uses all 4 twisted pairs to send both power and data to the edge IP device. The maximum power budget is 95W in the PoE system but the maximum remains power budget is 71W at the edge. In some of the applications such as all-in-one PC, the station could benefit from POE++. Still, there is too much power for most of the situation. How can we exploit the benefit of high-power PoE++? The PoE-powered switch could be one of the directions. The PoE-powered switch can power by another PoE Switch or PoE injector and expand the PoE ports. There 100 meters between PoE powered switch to the first POE switch, and there another 100 meters from PoE powered switch to the edge device. Not only the POE ports but also the distance has been expanded by using the PoE++ technology.

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There are two kinds of centralized PoE-powered solutions we can backup.

1.    PoE Switch Solution

The PoE Switch has a built-in power source to supply the power to the edge devices. The PoE switch uses a sharing power source. What we need to do is adding the UPS (Uninterruptible Power Supply) to supply the power to the PoE Switch, It becomes a backup power solution. The power budget of UPS depends on the power consumption from all edge devices plus the power loss inline. With managed PoE Switch, you can read the power consumption of each PoE port, simply add up all the ports to have the total power consumption in the system. While design the PoE Power system, it is always good to reseved some power buffer before you need to use 100% output.

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2.    PoE powered Switch

The PoE Power switch is the special equipment that works as both PD and PSE. The PoE powered switch can receive the power from the back-end PoE Switch and forward the power to the edge device. It increases the PoE distance from 100 meters to 200 meters, meanwhile expand the RJ45 ports at the edge. The PoE-powered switch provides the possible solution to backup the middle or large PoE-powered system. The radius is 200 meters far from the back-end PoE Switch. Thanks to IEEE802.3bt (PoE++), there is still about a 71W power budget at PoE powered switch. The middle and large PoE system backup become practical works. Now we can expand the PoE by using the PoE powered switch.

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