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Power Supply Comparison: Small Cells, Wi-Fi Hotspots, and HD Security-Camera Access

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Posted by James Donovan on 8 February 2017 Connect with James on LinkedIn Estimated reading time: 4 minutes

In the previous blog, we discussed the challenge of how to get power to devices in unusual places.

Another consideration is the type of power supply to use for powering the cable and how to safely and properly disseminate power off the other end to ensure delivery of the right energy levels to the network access devices.

For the power supply, there are three basic choices to consider: -48VDC NEC Class 2 or SELV compliant power supplies, 120/240VAC systems, and 380/400VDC Microgrid systems.

Power-supply Comparison

The -48V systems that remain within low power levels to meet electrical codes (such as NEC Class 2 and SELV) are desirable since they’re designed to keep energy levels low and as safe as possible. These systems can effectively handle power levels below 100W, so electricians are not required for the installation. Readily available from multiple vendors, -48VDC power supplies are a proven technology.

Because these systems keep power levels low, the drawback is that the inherent distances and power levels they can support are limited. Also, since the voltage level is so low, a higher electrical current is needed in the cable to drive power to devices. Higher current in the cable means more energy loss from heat caused by the electrical resistance in the copper. Still, these lower voltage DC systems are typically the best.

The 120/240VAC systems are also a proven technology, with standards in place for many years. These systems can support higher power and longer distances than -48VDC systems; however, they require qualified electricians for installation.

Other drawbacks include the inherently less efficient power transmission of AC systems due to capacitive and inductive effects, added difficulties in integrating UPS battery backup (requiring more equipment), and the requirement for AC transformers and additional AC-to-DC rectification circuits. Therefore, in most cases, AC systems are more expensive to deploy than -48VDC systems.

The 380/400VDC Microgrid approach promises a new, more effective way to handle higher power needs without the inherent inefficiencies of 120/240VAC systems. Systems have been deployed by major institutions around the world. Standards development is underway through the efforts of the EMerge Alliance (www.emergealliance.org/).

While the expectation is that this method will be overall less expensive, easier to connect, easier to maintain, and more energy efficient than AC systems, it will still require qualified electricians to install. For high power and long-distance applications where low-voltage NEC Class 2 electrical systems will not work, this method may be a good future alternative.

How much and how far?

Another important question to address is how much power can be delivered and at what distance to the network access device (small cells, Wi-Fi access points, HD security cameras, etc.)? With all power systems (AC or DC), the fundamental problem of voltage drop over distance must be addressed.

Until now, an electrical engineering calculation was typically performed for every cable run to ensure the voltage range delivered to the device was within the acceptable range. With modern DC/DC conversion technology, devices are now emerging that eliminate the need for this engineering.

Properly designed DC/DC conversion devices can take in a wide range of voltage and deliver exactly what’s required to power the device, whether it be a security camera or Wi-Fi access point.

Such new devices also incorporate the necessary types of carrier grade electrical protection to protect against lightning strikes, EMI surges, cable cutting, etc. These new devices promise to reduce engineering and make the systems install like “a long extension cord.”

Power questions answered

Deploying hybrid cable systems to power today’s network access devices should follow the same product life cycle typically seen in the FTTx industry. In the early 2000s when FTTx was just beginning, there was a multitude of unanswered questions, a lack of suitable products, and high deployment costs.

Today, these issues have been largely addressed through mature product systems provided by multiple vendors.

With the coming proliferation of network access devices, driven by 4G/5G, security, “smart homes,” and a host of other applications, there’s a strong need for robust, off the shelf systems to combine power and communications into single cables.

The speed of deployment, cost, safety, security, and other challenges must be taken into account by solution developers to remove these headaches for network designers.