Hot Time Summer in the City - Powering the Great Outdoors
One of my favorite songs from the 60's, yes I am dating myself, is the Lovin' Spoonful's is "Summer in the City." The opening lines of the song give a vivid description of just how hot it can get on a summer's day.
"Hot town, summer in the city
Back of my neck gettin' dirty and gritty
Been down, isn't it a pity?
Doesn't seem to be a shadow in the city
All around, people lookin' half dead
Walkin' on the sidewalk, hotter than a match head"
To convey the heat of the summer the band put their drums in the bottom of a building stairwell and the microphone on the top of the of the eighth floor to get that iconic sound that opens the song.
There are many devices today being placed outdoors that need to be powered. These include LED lights, Cameras, RFID Readers, Wireless Access Points, Radios of all kinds including Point to Point, Backhaul, LoRa and so many others. Today many of these devices are being powered by Power over Ethernet (PoE).
PoE was invented by PowerDsine in 1997 by introducing the first Power Source Equipment (PSE) semiconductor that put power onto an ethernet cable, and also the first Powered Device (PD) semiconductor that took the power off the cable and provided it to the device. Today, PSE semiconductors are found in PoE Switches, Gateways and Routers and many of the outdoor devices, including the ones listed above have PDs in them.
So when it comes to outdoor devices, how do you provide PoE power? Well the first option is to run an ethernet cable from a source indoors; however, based upon IEEE standards, the longest ethernet cable can be is 100 meters. So if the device is an RFID reader in the middle of a highway recording tolls, it is highly unlikely that there is an indoor environment close by to place a switch.
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The next most popular option is to place an switch in an outdoor enclosure. These enclosures are commonly known as a NEMA box. NEMA stands for the National Electrical Manufacturers Association. It publishes standards for booth indoor and outdoor enclosures of electrical and medical equipment. There are 13 levels of ratings, with sublevels, for all sorts of environments.
Just by placing a switch in such an enclosure does not mean it will function properly even if the enclosure is rated for outdoor use. First, NEMA enclosures must be able to open and close. Whenever you have a device that can be opened, it can allows elements such as dirt and dust in the box. The act of opening and closing the box puts wear and tear on the seal. If repeated frequently enough, the seal can fail. A worn seal can let in moisture that can severely damage the equipment. Additionally, enclosures that are going to be left out doors that can be opened increase the risk of tampering.
Then there are issues with the heat. Temperatures in such an enclosure can reach as high as 2 times the temperature outside. Most electrical components, unless designed for extremes will not be able to function under high temperatures. Certain electrical components such as capacitors are extremely sensitive to excessive heat.
Depending upon the geography, the device inside the enclosure might also be exposed to extreme cold. Most devices are not designed to work in sub-freezing temperatures. And the fluctuation from hot to cold can easily damage the equipment.
Also, it is not possible to just place a switch in a NEMA box. The device must be properly grounded. It must be protected against lightening strikes and power surges. And to dissipate some of the heat, fans may be deployed.
And when this is all done, you get a solution that will most likely still fail over time. The solution is to find a PoE Switch designed for the outdoors.
The first PoE Switch for the outdoors was introduced by the successor of the Microchip PoE Business Unit, in 2018. PowerDsine became the Microchip PoE Business Unit that same year. It was a IEEE 802.3 pre-bt switch with 4 PoE ports that could provide 60W of power. It also contained a fiber line port to transmit data over longer distances.
This past April, Microchip introduced the next generation of the PoE Outdoor Switch. This is an IEEE802.3bt unit capable of providing up to 90W of power. It offers 4 PoE ports and 2 fiber link ports. It is a Level-3 managed switch with full security features. The 2nd Fiber Link port provides the ability to daisy chain a run of switches with a return home so that if one link fails, there is always a path back to the source.
The switch is fully sealed so it cannot be opened and tampered also preventing dust and moisture from entering the switch. It is designed for extreme weather conditions hot or cold. It has surge protection, heat dissipation, and tolerance for cold built right in. And a real nice feature is it significantly smaller than placing a switch in an enclosure.
The result of this is an Outdoor PoE Switch that is rated with a Mean Time Between Failure of 150,000 hours at 25 degrees Celsius. This is significantly longer that an indoor unit placed in a NEMA box will last. And it is much safer, secure and reliable.
So the when deploying devices outdoors powered by a PoE switch, although it might initially be less expensive to use a standard switch in an NEMA enclosure, the likelihood of failure is high leading to replacement costs. That is why if safety, security, and reliability are the primary concerns, the best choice is to use a PoE Switch designed for the outdoors that if fully sealed and provides 2 Fiber ports.
To learn more about this next generation Outdoor PoE Switch visit https://www.microchip.com/en-us/product/pds-204gco