IP devices like VoIP phones, wireless access points, Pan-Tilt-Zoom (PTZ) security cameras have brought numerous advantages to people’s lives in various aspects. Typically, IP devices are powered through standard AC power or through Ethernet cables using PoE technology in outdoor environments. Today, we’re gonna address the issue of powering IP devices outdoors and explore different power solutions for long-distance outdoor deployments.
Choose PoE over AC power when powering IP devices
One of the biggest challenges of powering IP devices outdoors is the lack of available AC outlets. Places, where people plan to install the devices, do not necessarily have electrical infrastructures available at every endpoint. Moreover, the ambient temperature of outdoor settings also intensifies the danger of overheating in power units. AC power usually generates higher electrical currents, which makes it more prone to overheating and sparking which will cause potential fires and power surge. When irresponsibly used or applied in an easily combustible circumstance, it will explode when the charger heats up.
Power over Ethernet (PoE) technology provides both electrical power and data connection (10/100/1000 Mbps) to the terminal devices on twisted-pair Ethernet cabling at a maximum distance of 100m/328ft, which eliminates the need for additional electrical infrastructure and traditional wiring with great flexibility on installation. Besides, PoE only carries a relatively low voltage of 60V with a user-friendly plug-and-play design, which makes the installation easier and faster with decreased electrical hazards and reduced costs of hiring professional electricians. Compared with the traditional power supply like AC power, PoE doesn’t need a separate power line to run the terminal devices, which contributes to a substantial reduction in installation costs with a more reliable and safer power connection.
How does the PoE switch deliver power for IP devices?
A complete PoE system is composed of two parts: power sourcing equipment (PSE) and powered devices (PDs). PSE refers to devices that deliver power to the connected devices on different PoE standards to facilitate installation and management in different scenarios, from commercial applications like VoIP phones, IP cameras to industrial applications like access control systems. The most common PSEs are network switches (also known as endspans) and PoE injectors (midspans), intermediary devices that supply power from/to non-PoE devices. Among all, the PoE switch has progressed as an efficient medium for both power and data connection for IP devices via a single Ethernet cable. On the other hand, PDs are devices that receive power from the PSE, the client of the entire PoE system. Additionally, most powered devices will have an auxiliary connector for external power supplies as a backup in case the PoE power system fails.
Working process of PoE switches for power supplies
The following steps are the working process of PoE switches to supply power to PDs.
Detection of the PDs: At the beginning, the PoE switch will send a proper voltage pulse to the terminal devices to detect whether the electrical power is compatible between the PSE and PDs, or in other words, to check whether the remote devices is PoE-compatible or not. If the answer is negative, the switch will not deliver power to the faulty terminal devices (only data transmission allowed) to prevent potential damages to non-PoE devices. It is worthwhile to mention that this negotiation or communication process is only available in active PoE switches, which are rated to be IEEE 802.3af, IEEE 802.3at or IEEE 802.3bt compliant, whereas passive PoE switches, also known as non-standard switches, do not adhere to any IEEE standard and supply power to PDs at a certain voltage regardless of the compatibility.
Classification of the PDs: To prevent over-powering the terminal devices which will shorten the service life of the connected units, IEEE-complaint PDs can be roughly categorized into different classes depending on their power requirements to prevent the terminal devices from drawing more power than they actually need. PoE classes play a pivotal role in ensuring efficient power distribution by measuring the amount of power a PD requires and thereby allowing PSE to reallocate surplus power to more power-hungry terminal devices to achieve the optimal allocation of existing power. And there is something that shouldn’t be neglected that measured power on PSE is always slightly higher than PDs for voltage loss attributed to power dissipation (power loss as heat). The switch will automatically classify the PDs on the rankings of 0-8 and deliver power to the devices accordingly. A terminal device that is classified as Class 3 will receive 6.49-12.95 watts of power, while the PSE will actually supply 15.4 watts, with a power loss of at least 2.45 watts. The following chart indicates the amount of power allocated to different classes.
Start to power-Power off: After measuring the amount of power each terminal device needs, the switch will start to provide a low voltage to the PDs (typically less than 15 microseconds) and then gradually increase to the full 48V DC power. After the voltage is raised to 48V, the PoE switch will provide uninterruptible power to the PDs. Therefore, in this way, either the PSE or PDs can get the maximum power protection to prevent the situations of overload or underload. Since the switch is hot-swappable featuring simple plug-and-play installation, users can replace or unplug the device without taking the device offline or disconnecting the power. When the powered device is removed or short-circuited (overloaded or out of power budget), the PoE switch will cut off the power supply (usually within 0.3-0.4 seconds) and re-enter the detection procedure so as to ensure the ongoing functionality of devices.
4 ways to power IP devices outdoors using PoE equipment
As previously mentioned, using AC power to set up outdoor IP devices is not only infeasible (no available AC outlets) but also hazardous (overheating-explosion). But all of these hazards can be eliminated by using PoE to secure the normal functioning of both PSEs and PDs.
#1 indoor power supply equipment+a solid copper cable
With PoE, people can remotely provide steady and reliable power sources to the terminal devices in a climate-controlled setting (i.e. the control room) by simply connecting the PSEs (PoE switch, injector, etc.) with the terminal devices via a single copper cable (Cat5/6). But do remember to choose pure copper Ethernet cables over copper clad aluminum (CCA) cables because CCA cables suffer more considerable depreciation than solid copper cables, which leads to significant attenuation and re-transmission. Worse still, CCA cables have severe DC resistance with more power converted into heat energy during transmission. On the contrary, solid copper cables suffer less signal and power loss over long-distance data and power transmission with immunity to adverse weather conditions or corrosive elements.
#2 PoE++ switch+Outdoor PoE switch as a passthrough switch+Ethernet cables
Normally, the standard PoE switches only support IEEE 802.3af/at with a maximum power supply of 12.95/25.5W, so a PoE++ switch is highly recommended to power more demanding terminal devices or multiple low-wattage devices like static surveillance cameras. Contrary to PoE and PoE+ devices, the PoE++ switch delivers power in a two/four-twisted-pair copper cable with a maximum power supply of up to 51W under Type 3 and 71W under Type 4 to remote IP devices. It is universally acknowledged that the maximum distance of the Ethernet cable is 100m/328ft, so an additional PoE switch can be applied as a transfer stop for extension, for the outdoor PoE switch can receive energy from another PoE switch and provide power for the PDs. The installation is quite simple: connect the indoor PoE++ switch to the outdoor passthrough switch with a 100m Ethernet cable and then connect the outdoor switch to the terminal devices with another cable.
#3 media converter+fiber cables+PoE switch with SFP slots+Ethernet cable
One of the minor downfalls of PoE in long-distance deployments is that its speed will gradually degrade (slow down to 10 Mbps/s) as the distance increases, while the fiber optic system has a world-renowned reputation for high-speed data transmission over long distance (up to 10 km-80 km) at a speed of 1000 Mbps/s (will be compromised if using not compatible routers or devices). Since fiber cables transmit data through light (laser or LED), it’s immune to electromagnetic interference which will lower the chances of attenuation (signal loss). To set up IP devices with fiber optic cables, a media converter and SFP transceivers are needed to convert the digital signals to optical signals, or vice versa. And for simple installation, it’s highly recommended to use pre-terminated fiber optic cables. Since fiber cables only transmit data, a power supply is needed to power the PoE switch at the network edge. First, connect the media converter (connected to the power) with the outdoor PoE switch by inserting the transceivers into the SFP slots on both sides and using pre-terminated cables for connection; then, power the outdoor PoE switch and connect it with the PDs with an Ethernet cable.
#4 media converter+fiber cables+PoE outdoor media converter+Ethernet cable
Voltage drop (VD) is a common problem in long-distance cable running, especially on larger properties (i.e. farms). It is the loss of voltage at the end of a run of the cable caused by the flow of currents going through a DC resistance. In fact, cables of any length or size have some DC resistance, which will grow in proportion as the distance increases. And technically, when the copper cables heat up due to a higher running current or a sudden rise in temperature, their resistance also increases, which leads to a higher voltage drop. Too much VD will result in poor performance of PoE equipment because of low voltage and sometimes cause safety hazards (overheating and arcing). To reduce power loss in a circuit, larger-sized copper cables are needed, and it’s highly recommended to use the VD calculator to find out the optimal cable size to reduce unnecessary power loss while remaining cost-effective. Another solution is to shorten the length of the power cord by moving the power source back to the network edge. The PoE media converter is designed for digital-optical signal conversion while able to provide power to the terminal devices (once connected to the power source). And a power regulator is pre-designed in to ensure stable power output regardless of voltage fluctuation. First, connect the media converter with the PoE outdoor media converter with pre-terminated fiber cables; then power the PoE media converter and connect it to the terminal device.
Troubleshooting PoE power supply
If the PoE is powered off without cause, the following steps are suggested for diagnosis:
1.Check if the powered devices support PoE——Incompatible or non-PoE devices cannot receive PoE power from PSE, and unmatched connections will burn down the devices.
2.Check if the PDs exceed the maximum power supply——If the PSE only supports IEEE 802.3at with a maximum power supply of 30W on a per-port basis (25.5W to the PDs), a PD that requires more power than 25.5W then cannot receive enough power to start up. When irresponsibly used, the connected device could be damaged by underload and unstable power.
3. Check if the wattage of all connected devices exceeds the power budget——A 16-port PoE switch with a power budget of 200W can simultaneously power 12 devices with PoE/IEEE 802.3af standard (12×15.4W=184.8W<200W) but can only power 6 devices with PoE+/IEEE 802.3at standard (6×30W=180W<200W) at one time.
