Although the various benefits of LED lighting are self-evident, efficient power supply methods are still controversial. This article focuses on the use of modern Power over Ethernet (PoE) technology to provide DC power to LED lighting. If you use a local area network (LAN) to network your lights, PoE technology will play its part and achieve the best interests.
The LED is essentially a low voltage DC device. To ensure compatibility with traditional AC power supplies, most LED drivers for illumination use AC/DC converters to convert AC power to a lower DC voltage. This conversion process reduces system efficiency, so designers have proposed a DC-based power system. Several studies have compared common AC systems with DC power systems. A study by the University of Carnegie Mellon University 2 found that using DC power saves $2,000 per year compared to using AC. If the LED is powered by a grid-connected solar PV power source, DC is used compared to the use of AC power. Save $5,000 a year."
Now, according to the IEEE802.3 standard, which was first released in 2003 and updated in 2009, you can use PoE technology to provide DC power for LED lighting. The standard specifies that a single standard network cable (such as Cat5) can be used to directly power and communicate data to connected devices, and provide power through a power supply (PSE) on the switch/hub. The powered networking device (in this case, the LED lighting) is called a powered device (PD).
To account for network cable losses under worst-case operating conditions, the PSE provides a power supply that is higher than the power limit of the PD. The original PoE standard (IEEE 802.3af) stipulated that PSE power supplies use Cat3 or higher cable to provide a maximum of 15.4W in the 44VDC to 57VDC range. In this case, the PD is limited to 13.0W and the voltage range is 37VDC to 57VDC. Subsequent IEEE802.3at standards increase power to 30W (PSE) with voltages ranging from 50VDC to 57VDC, using Cat5 or higher. At this time, the PD is limited to a maximum of 25.5W and the voltage range is 50VDC to 57VDC. The IEEE802.3bt standard, which is expected to be approved soon, will further increase PoE power, with a minimum power of 90W for the PSE output port.
When powered by PoE, each LED luminaire can be a standard RJ-45 connector plug-and-play device with its own independently addressable IP address. Not only that, but by adding sensors to LED luminaires, you can convert them from pure lighting to smart LED concentrators. With this configuration, each "smart" LED concentrator collects information about ambient light, temperature, humidity, and anonymity and returns it to the controller. For example, personnel detection ensures that lighting is turned on when someone enters the room, and that lighting is turned off when no one is in the room. Ambient light sensors also support daylight harvesting 5, as well as adjusting LED illumination to maintain constant brightness in the absence of daylight.
PoE is ideal for powering, connecting and controlling smart LED concentrators over a LAN. In this way, LED lighting systems become part of the IT network; through any networked device (such as phones, tablets, PCs), its services will not only be limited to users, but extended to other building services. Then, the user can use the proximity detection sensor of the system to find the nearest free conference room. It can even bring greater benefits to facility owners and managers to get an overall picture of the facility's energy usage. By implementing all nodes of the measurement, monitoring, and control network, including heating and ventilation, managers can identify opportunities to improve energy efficiency and operational efficiency. With this information, the manager can adjust the temperature, lighting, and cleaning schedule based on the user's historical behavior data.
Another benefit is that the PoELED network can adapt to future developments. LED lighting fixtures (and associated smart sensor concentrators) have been installed to the desired location, and power and data have been connected to most useful locations. Therefore, new sensors or communication modules, such as distributed short-range wireless access points, can now be added with low marginal cost and relatively low labor.
What does this mean for us? Obviously, using PoE can reduce the cost of deployment and installation of IP-enabled devices, whether they are sensors or LED lights. Since the data and the power supply share the same cable, the wiring cost is reduced; since the installation of the network cable does not require a qualified electrician, the installation cost is also reduced; compared with 110 VAC (or 220 VAC), the PoE DC voltage risk is greatly reduced, so the installation is performed. The process is also safer. PoE networks support better overall network power management: both discrete control through the power of the connected devices and power backup using only network connections during power outages. The 47th SuperBowl Championship is an example of the added value of PoE technology, when the power outage caused lighting and elevator downtime for 35 minutes7. During the period, the stadium's WiFi network was unaffected because the network was powered by PoE and had battery backup.
All of these benefits of the PoE lighting system have actually reignited the discussion of AC and DC power. Some people ask, “How do you deal with the resistance loss caused by Cat5 (or higher) cables?†Some people say, “If you remove the additional AC/DC conversion stages currently required in AC power systems, these losses are sufficient. Is it low enough to achieve considerable efficiency improvements?"
To analyze this controversy, we analyzed three scenarios for powering 10W and 20W LED illuminators: two of them based on the original IEEE802.3af (15.4WPSE and 13.0WPD) and the subsequent IEEE802.3at (30W and 25.5W) The standard is used for power supply; the AC power supply uses 230VAC standard power.
PoE scenario: The effect of cable length on efficiency
The CUIINCPSE-1000 is powered by 230VAC mains, which has a power of 1000W and a typical efficiency of 90%. The PSE is powered by a 40W MAX5984PSE controller and the PD uses a 70W MAX5982 controller. The cable is a Cat623AWG cable with a resistance of 67 ohms per kilometer or 0.067 ohms per meter per line.
For LED drivers, we use 95% efficiency in our calculations. Actual efficiency may be higher, as shown in Figure 1.
LED lighting is now the mainstream technology and is gradually replacing incandescent, halogen and compact fluorescent lamps (CFLs) in commercial, industrial and residential sectors. The benefits of LEDs are well known, including longer life, higher energy efficiency, and very small lamp sizes. For example, LED lights can last up to 50,000 hours, while incandescent lamps typically last 1,000 to 2,000 hours, and CFLs have lifetimes of 5,000 to 10,000 hours. Due to the long service life, LEDs reduce operational/safety risks and labor costs due to the replacement of hard-to-reach lights. The cost of using LEDs is also much lower. The brightness of 10W LEDs is about the same as that of 60W incandescent bulbs.
DC power supply using PoE technologyThe LED is essentially a low voltage DC device. To ensure compatibility with traditional AC power supplies, most LED drivers for illumination use AC/DC converters to convert AC power to a lower DC voltage. This conversion process reduces system efficiency, so designers have proposed a DC-based power system. Several studies have compared common AC systems with DC power systems. A study by the University of Carnegie Mellon University 2 found that using DC power saves $2,000 per year compared to using AC. If the LED is powered by a grid-connected solar PV power source, DC is used compared to the use of AC power. Save $5,000 a year."
Now, according to the IEEE802.3 standard, which was first released in 2003 and updated in 2009, you can use PoE technology to provide DC power for LED lighting. The standard specifies that a single standard network cable (such as Cat5) can be used to directly power and communicate data to connected devices, and provide power through a power supply (PSE) on the switch/hub. The powered networking device (in this case, the LED lighting) is called a powered device (PD).
To account for network cable losses under worst-case operating conditions, the PSE provides a power supply that is higher than the power limit of the PD. The original PoE standard (IEEE 802.3af) stipulated that PSE power supplies use Cat3 or higher cable to provide a maximum of 15.4W in the 44VDC to 57VDC range. In this case, the PD is limited to 13.0W and the voltage range is 37VDC to 57VDC. Subsequent IEEE802.3at standards increase power to 30W (PSE) with voltages ranging from 50VDC to 57VDC, using Cat5 or higher. At this time, the PD is limited to a maximum of 25.5W and the voltage range is 50VDC to 57VDC. The IEEE802.3bt standard, which is expected to be approved soon, will further increase PoE power, with a minimum power of 90W for the PSE output port.
When powered by PoE, each LED luminaire can be a standard RJ-45 connector plug-and-play device with its own independently addressable IP address. Not only that, but by adding sensors to LED luminaires, you can convert them from pure lighting to smart LED concentrators. With this configuration, each "smart" LED concentrator collects information about ambient light, temperature, humidity, and anonymity and returns it to the controller. For example, personnel detection ensures that lighting is turned on when someone enters the room, and that lighting is turned off when no one is in the room. Ambient light sensors also support daylight harvesting 5, as well as adjusting LED illumination to maintain constant brightness in the absence of daylight.
PoE is ideal for powering, connecting and controlling smart LED concentrators over a LAN. In this way, LED lighting systems become part of the IT network; through any networked device (such as phones, tablets, PCs), its services will not only be limited to users, but extended to other building services. Then, the user can use the proximity detection sensor of the system to find the nearest free conference room. It can even bring greater benefits to facility owners and managers to get an overall picture of the facility's energy usage. By implementing all nodes of the measurement, monitoring, and control network, including heating and ventilation, managers can identify opportunities to improve energy efficiency and operational efficiency. With this information, the manager can adjust the temperature, lighting, and cleaning schedule based on the user's historical behavior data.
Another benefit is that the PoELED network can adapt to future developments. LED lighting fixtures (and associated smart sensor concentrators) have been installed to the desired location, and power and data have been connected to most useful locations. Therefore, new sensors or communication modules, such as distributed short-range wireless access points, can now be added with low marginal cost and relatively low labor.
What does this mean for us? Obviously, using PoE can reduce the cost of deployment and installation of IP-enabled devices, whether they are sensors or LED lights. Since the data and the power supply share the same cable, the wiring cost is reduced; since the installation of the network cable does not require a qualified electrician, the installation cost is also reduced; compared with 110 VAC (or 220 VAC), the PoE DC voltage risk is greatly reduced, so the installation is performed. The process is also safer. PoE networks support better overall network power management: both discrete control through the power of the connected devices and power backup using only network connections during power outages. The 47th SuperBowl Championship is an example of the added value of PoE technology, when the power outage caused lighting and elevator downtime for 35 minutes7. During the period, the stadium's WiFi network was unaffected because the network was powered by PoE and had battery backup.
All of these benefits of the PoE lighting system have actually reignited the discussion of AC and DC power. Some people ask, “How do you deal with the resistance loss caused by Cat5 (or higher) cables?†Some people say, “If you remove the additional AC/DC conversion stages currently required in AC power systems, these losses are sufficient. Is it low enough to achieve considerable efficiency improvements?"
To analyze this controversy, we analyzed three scenarios for powering 10W and 20W LED illuminators: two of them based on the original IEEE802.3af (15.4WPSE and 13.0WPD) and the subsequent IEEE802.3at (30W and 25.5W) The standard is used for power supply; the AC power supply uses 230VAC standard power.
PoE scenario: The effect of cable length on efficiency
The CUIINCPSE-1000 is powered by 230VAC mains, which has a power of 1000W and a typical efficiency of 90%. The PSE is powered by a 40W MAX5984PSE controller and the PD uses a 70W MAX5982 controller. The cable is a Cat623AWG cable with a resistance of 67 ohms per kilometer or 0.067 ohms per meter per line.
For LED drivers, we use 95% efficiency in our calculations. Actual efficiency may be higher, as shown in Figure 1.
Figure 1: Efficiency curve of the MAX16832LED driver
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