We all have a fair weather friend that only participates when conditions are just right. Delivering Power over Ethernet (PoE) is a technology that, like a fair weather friend, may not be well suited for all outdoor weather conditions.
Contributed by | Delphi Display Systems
History of Delivering Power to Electronic Devices
Since electric power distribution was being developed at the same time as the first telephones, the phone system could not rely on there being electric power at every end point. As a result, early phones had their power delivered directly over the telephone “data” wires. Over time, phones became more sophisticated with wireless handsets, caller ID screens, integrated answering machines and the like. All of these features required more power than was available from the phone line, so they had to be plugged into the 120VAC wall outlet for power. With the build out of the electric grid, 120VAC power became plentiful and available just about everywhere, making it the power source of choice for just about all power hungry electronic devices.
Telephones eventually migrated from analog signals to digital signals with the introduction of digital IP based phones. IP phones did not connect directly to the “Ma Bell Phone System,” but instead connected to a company’s digital “Ethernet” computer network. In 2003, the Institute of Electrical and Electronics Engineers (IEEE) issued its 802.3af specification to use the spare pairs of wire in a CAT5 Ethernet cable to supply limited power to IP phones and other indoor devices like IP cameras. The initial specification allowed for up to 15 watts of power to be transmitted. In 2009, the specification was updated to PoE+ (802.3at) which supplies up to 25 watts of power to the phone or other endpoint device, comparable to the amount of power used by the light bulb in the back of a refrigerator!
Since 2009, some companies have produced non-standard proprietary PoE systems that can deliver more than 25 watts of power. However, non-standard means just that, these solutions will only work with that one manufacturer’s equipment and no other.
History of Outdoor Order Confirmation Displays
In 1995, the Quick Service Restaurant (QSR) industry began to deploy outdoor video displays in the drive thru lane to show customers exactly what they were ordering. Rather than going with a fair weather product, the major QSR brands including McDonald’s, Taco Bell and others wrote a specification for a “one-size-fits-all” solution. The specification standardized the size of the screen, the mounting hardware and operating environment. Since quick service restaurants are located all over the country, from the cold of an Alaskan winter, to the scorching heat of an Arizona afternoon, the industry mandated that Order Confirmation Displays start and continue operating from a low of -40°F to a high of 140°F all while being subject to snow, rain, dust, wind and direct sunlight.
Because of these requirements, Order Confirmation Displays have relied on 120VAC as a steady and stable source of power.
On a Cold Winter Night
Outdoor displays can be exposed to very low temperatures. Below -10°F, liquid crystal displays respond slower and will refresh their images erratically, resulting in a poor user experience. At -20°F, the liquid crystal material can freeze, causing the display to stop functioning and may cause permanent damage. Add wind to the mix and the situation is even worse. Since it is not uncommon for quick service restaurants to shut down all their lights after hours, for many northern and mountain locations it may be required that the outdoor display start up and operate after it has been frozen to -40°F for several hours.
For these reasons, it is critical that outdoor displays be equipped with internal heating elements that will insure that the LCD stays within its normal operating limits in low ambient temperatures. At a minimum, electric heaters require 60 watts of power to heat up a 15” display enclosure from -40°F and keep it warm enough to operate properly.
High Noon in the Desert
In many parts of the world, outdoor displays can be subject to very high ambient temperatures. In addition, the sunlight beating down on the front glass can add 70°F to the temperature of the LCD, on a 110°F day that means the LCD is frying at 180°F, well above the QSR max temperature of 140°F. In order to prevent damage to the LCD, the heat must be removed from the liquid crystal material. To accomplish this, one design approach utilizes a gap between the exterior glass and the surface of the LCD. Air is circulated across the front of the LCD, removing heat buildup to prevent overheating, where the display goes “isotropic” and the picture turns black. This solution requires additional power to run a fan inside the order confirmation display, and may require additional fans in the speaker post, menu board or canopy system.
Non-Standard PoE Technologies
As mentioned above, PoE+ can deliver up to 25 watts of power, but that is typically not enough to drive a 15” LCD with enough brightness to be readable in direct sunlight. Non-standard, proprietary PoE power injectors can boost the power delivery above 25 watts, but not without some important technical problems, including:
- Overheating the Data Cable – CAT5 cables are made with relatively thin 24 gauge wire. Typical installations require 150 feet of CAT5 cable. Pushing 60+ watts of power through these wires can cause them to overheat and melt.
- Crimping – CAT5 cable is typically terminated by crimping on an RJ45 connector. This is fine for low power connections, but can result in arcing and other problems with high power connections.
- Multiple Points of Failure – PoE ultimately gets its power from a 120VAC source, so PoE adds several additional points of failure to the power circuit:
- 120VAC – Power connects from the 120VAC outlet to the OCS power cord. (1 point of failure)
- PoE – Power connects from the 120VAC outlet to the PoE injector power cord, from the power cord to the PoE injector, from the PoE injector to the PoE hub (if required), from the PoE hub to the CAT5 cable going out to the post, and finally from the CAT5 cable RJ45 connector to the order confirmation display (4-5 points of failure)
- Wasted Energy – For a typical 150ft. CAT5 cable run, as much as 6% of the power is dissipate in heat in the cable, making the PoE solution only 94% as efficient as a 120VAC power source where there is no wasted energy in the wiring.
- Not Meeting -40°F to 140°F Specification – Even proprietary, non-standard PoE solutions cannot deliver enough power to meet the QSR industry’s current operating temperature standard -40°F to 140°F requirement.
So given the above limitations, why would anyone consider PoE for a drive-thru outdoor order confirmation system? The main reason is the prospect of only having to run one CAT5 cable out to the speaker post or menu board instead of both a CAT5 cable and a 120VAC power line. This can save hundreds of dollars in those situations where there is: 1) an existing speaker post that does not have 120VAC; and 2) has space in its conduit to pull an additional CAT5 cable. However, in most other cases the site prep savings are minimal or non-existent. For example for a totally new store, or new drive thru build, the contractor already has to dig a trench to run the conduit for the CAT5 cable out to the post or menu board, dropping in a second conduit for a 120VAC line can be done for very little additional cost.
When you compare these technologies side-by-side, the reduced installation cost benefit of a non-standard PoE solution is far outweighed by the technical issues it introduces.
If PoE is not well suited for harsh outdoor weather environments, what “fair weather” environments make sense for this technology? PoE is perfect for indoor use, with digital electronic devices that do not consume significant amounts of power. One example is the indoor PoE powered interactive kitchen display that can be used to control and monitor a variety of store activities, which Delphi is introducing in 2013. This use of PoE provides the benefit of being able to mount the display anywhere in the store regardless of its proximity to a 120VAC outlet. When it comes to outdoor uses, the QSR franchisee should double check their requirements and the manufacturer’s specifications to make sure they match up, taking into account operating temperature, reliability and other issues.
About Delphi Display Systems
Headquartered in Costa Mesa, California, Delphi Display Systems designs and manufactures a wide variety of outdoor digital signage products serving the quick service restaurant (QSR), petroleum retail, and other market verticals. Applications include drive-thru order confirmation, digital menu boards, gas-pump top video displays, outdoor information kiosks and more.
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