HWg-STE2 Use Case: Powering With PoE

The Problem

Need to place a sensor where there’s no power? Want to ensure your sensors stay running when mains power goes out?

The Solution

PoE (Power Over Ethernet) saves the day! Centralize your power supply to your network closet/rack, and push the power right through your ethernet network to the devices, eliminating the need for a bulky plug where the sensor lives!

Even better, if your closet/rack power supply is connected to a UPS, your sensors will keep running even when the normal A/C power cuts off during an emergency.

Use Case: A Fridge Too Far

In our situation here, we’d like to keep track of the office fridge temperature, in case there’s a power failure, or someone foolishly leaves the door ajar. Whatever the problem is, we want to know when the temp drops so we can do something before things are ruined – just as you might in your restaurant, manufacturing complex, bio/chem lab, and countless other places.

Here you’ll notice: we have two power plugs, but not only are they both taken, they’re not connected to any kind of Uninterruptible Power Supply (UPS). So even if we plugged in an ugly power strip and powered our sensors here, the sensor would die if the power failed – and we wouldn’t get our notifications!

We do, however, have an ethernet jack that winds its way back to our rack closet a short way away. Thanks to the flexible magic that is Power Over Ethernet, we can use a PoE Injector in the closet, connected to our UPS, and all we’ll need next to the fridge is our ethernet jack, which will provide the sensor with both data and power in one cable.

Note: The STE2 also supports WiFi as well. So if your situation is reversed – and you have power, but no ethernet service, you can power the device (perhaps with a small UPS at the location for backup), and use WiFi for network connectivity! Just be sure your WiFi and Network infrastructure have power during a power failure.

The Injector

We chose the TP-Link POE150S and use it a lot for the STE2. The device itself is quite small, and uses a traditional ‘wall-wart’ power supply.

The blue ethernet cable connects between the unit’s “LAN IN” port and our main switch in the rack closet.
The red side connects to the patch panel that carries ethernet out to the wall jacks.
However your rack/closet is configured, you’ll want to ‘insert’ the PoE Injector between your switch and the endpoint where you want to plug in your STE2 – in our case, the plug beside the fridge.