Choosing the right PoE device and understanding how to power it

Choosing the right PoE device and understanding how to power it

Power over Ethernet provides power to end devices. To accomplish this, you need a PoE enabled switch that can supply enough output power, complies with the right standards, and is the right device for your system. In turn, powering a PoE switch is often overlooked, but it is crucial. 

It is common for industrial PoE switches to be installed in harsh locations and may be subject to unstable input sources, especially in the On-board rail industry.

Protect your PoE Device 
To protect such PoE switches, surge protection is often used and helps protect PoE enabled switches and the connected devices from unforeseen electrical damage. It also helps reduce downtime and prevent costly repairs. 

This is important as it can help prevent damage from power spikes or surges caused by lightning strikes, faulty wiring, or malfunctions. Without surge protection, PoE switches may become damaged, and the connected devices may suffer from data loss, system crashes, and other issues.

Maximum total output and per port 
PoE devices are measured on both the maximum total output and the output per port, both in Watts (W). As an example, the Lynx 3510 has a total output of 240W, and provides up to 30W per port (8 ports in total).

As an alternative, the Viper PoE range has a maximum output of 80W. The Viper PoE range has 8 ports as well, but this does not mean that the maximum output per port is 10W, it is in fact 30W. However, the Viper PoE Range has a power margin of 80W, which is shared between the 8 ports. Not all end devices require maximum output on usage, which means that 80W is sufficient in most on-board applications. A typical camera in an on-board application is between 5W to 10W, which fits well within the 80W total power margin. 

The advantage of a PoE switch with a higher maximum total margin is that it enables much more power-hungry devices in the field. Commonly, devices do not utilize the full 30W, only drawing what they need. 

A problem may occur when some external PoE devices try to draw too much power. Within Westermo’s operating system, WeOS, the maximum output per port can be configured and tailored to each device, ensuring the power budget is not depleted.
PoE standards and why they are important
There are two main PoE standards. The technical name for these is 802.3af and 802.3at, or PoE and PoE+ respectively. 

The 802.3af standard was the first version of PoE and limits the maximum draw to 15.4W per port. Devices that comply with this standard are known as Type 1 devices. Typical examples of these kinds of devices can be Voice over IP (VoIP) phones or lower resolution IP cameras.

802.3at expanded PoE to PoE+ and increased the maximum draw to 30W per port. Devices that comply to this standard are known as Type 2 devices. They could be IP Cameras with a much higher resolution with Pan, Tilt & Zoom (P-T-Z), video phones or alarm systems.

The Lynx 3510 and the Viper PoE range both support PoE and PoE+ as a standard.

Selecting the right device for your application
The Lynx 3510 PoE is a DIN rail PoE device designed for a wide range of applications. These applications range from trackside, to energy, and water & wastewater, just to name a few. The switch is designed with the harshest industrial environments in mind and is capable of withstanding extreme temperatures, vibrations, humidity, and electrical environments. 

The Viper PoE range is specifically designed for the on-board rail market, and in the very harsh environments in which you find mining and cranes. The range is designed to IP 67 which allows for the device to temporarily be submerged in water up to a 1m for 30 minutes.
Choosing the right power supply
PoE switches can require more voltage than standard switches and routers. Traditionally, most industrial devices require an input voltage of 24VDC to 48VDC. PoE switches that can output 30W per port, such as the Lynx 3510, require a minimum voltage input of 53VDC. 

Interestingly, our Viper PoE range has an input voltage range from 24VDC to 110VDC. As this range is regularly used in on-board rail applications, an environment that is far harsher than standard applications, the input voltage is much vaster than the Lynx 3510. 

It is important to know which power supply to select when purchasing a PoE device. If this is done incorrectly, external devices may not receive the correct power and, therefore, will not function. 

Choose correct PoE device: 

Product Viper PoE Lynx 3510 PoE
Input 24 to 110VDC  53 VDC
Max PoE Output 80W  240W
Port count 8 8
PoE Version 802.1at & af (PoE/PoE+) 

802.1at & af (PoE/PoE+)

Industry On-board/Mining Trackside, Energy, etc
Max output per port 30W 30W

When using PoE enable devices, the supply and installation is just as important as the switch itself. Without proper protection or power, you will reduce the lifespan of the product and in some cases damage it. Correctly selecting a power supply and in some cases surge protection provide a foundation for most PoE applications.

Power budget and standards are good to know, and it is always good to check that the PoE device can handle the end device. Westermo PoE devices are PoE and PoE+ enabled, and range in PoE budget from 80 to 240W, depending on the unit.

Nuri Shakeer

International sales

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