Power supplies are a basic component of surveillance and security systems - but they are often taken for granted. It goes without saying that each product has specific power requirements and operating range, and there are numerous variables to consider when determining how to provide power, given the various solutions which have evolved for today's advanced integrated security systems.
The sheer number of power supply products available can be a challenge to evaluate relative to the actual power requirements of the numerous devices that comprise a system. Understanding more about power supplies and how they are incorporated into various systems and configurations can provide strategic value when designing and implementing professional security systems.
This article will shed light on the expansive range of power system products. It will outline the selection of a power supply that meets specific product needs; the importance of quality and reliability on product and system performance; the benefits of centralized power systems; and how power systems can improve efficiency and lower overall costs.
Selecting a Power Supply Solution
The "How Stuff Works" Website (howstuffworks.com) compares the flow of electricity to the flow of water through plumbing pipes. The three basic units of electricity are voltage (measured in volts), current (measured in amps) and resistance (measured in ohms). When comparing electrical current to water flowing through plumbing, it is helpful to think of the voltage as the water pressure, the current as equivalent to the flow rate and the resistance as similar to the pipe size. Increasing the voltage will make more current flow in the same way that higher water pressure will push more water through a garden hose. Electrical power is measured in watts, which is the voltage multiplied by the current - increasing either will boost the resulting power. Beyond the basic physics dealing with electricity, there are several critical issues to address when selecting a power supply for professional security applications:
- What type of cabling is being proposed for the project? Does it conform to the system's needs?
- What is the distance between the power source and the device it is powering?
- What are the voltage and current requirements of the device and the estimated voltage drop due to wire size and distance?
- Does the device require isolated power?
- Will the power supply be subjected to harsh environmental conditions?
- How much additional power above and beyond the device's requirements should be added as a safeguard? (Altronix typically recommends a power supply can provide 20 percent more power than the system requires).
- What agency approvals are required and which codes need to met?
The fact is that every security system is different, and every system requires a power supply product - or combination of products - specific to its needs. As a result, there is an extensive selection of power supply products available. To illustrate the number of products involved, consider that the Altronix Product Guide includes more than 150 pages of solutions. The breadth of choices ensures that a system designer/integrator can match the power supply that best satisfies the requirements of each product in their system.
Reliability Is Critical
Serving a mission-critical function in today's companies and institutions, security and surveillance systems cannot afford to stop operating in the event of a power outage. One of the basic requirements of power systems is to provide reliability and continuous security system operation. If a camera never blinks, it is in part because there is a power system that keeps it from doing so. An uninterruptible power source (UPS) is integral to continuous system operation. A UPS includes a battery backup to provide uninterrupted 24VAC for cameras during normal, brownout and power fail conditions. Other components of reliability include short circuit and overload protection and fused or resettable PTC-protected outputs (a positive temperature coefficient [PTC] element is a power supply circuit breaker).
System reliability also depends on knowing exactly what is going on related to a system's various power supplies. Sometimes power system status is communicated locally or remotely. Alerting security personnel of system status in real time enables personnel to react quickly and efficiently, and helps reduce costly system downtime and maintenance.
Centralizing Power Supply Systems
Systems can gain design efficiencies by centralizing the management of power supplies. Supplying power to multiple systems using a single power supply can minimize cost and make the system easier to monitor, use and manage.
One way to centralize a power supply system is by leveraging the unshielded twisted pair (UTP) cable that is sometimes used to transmit video and data signals back and forth from video cameras to a central location. Video surveillance systems using UTP employ video baluns (transceivers) at each camera to convert the video signal from the coaxial output of the camera to enable it to travel along with data (RS-422/RS485 to direct pan/tilt/zoom, camera controls, etc.) to a centralized transceiver hub. The hub takes the signals from various cameras and transitions them back to coax to be used by a DVR or video multiplexer.
Transceiver hubs can also provide power to the cameras across the UTP cable by way of a centralized power source, thus eliminating the need for an individualized power source at each camera. Using transceiver hubs with integral camera power - such as the HubWay Series from Altronix - also provide system operators with video signal and power status for each camera in the form of LED indicators.
Another way to centralize power supplies is by using Power-over-Ethernet (PoE) with IP-based networked systems. As technologies for the security industry transition to a networked environment, the market demand for integrated systems on a network platform has gained significant traction as users become aware of the enhanced functionality and lower total cost of ownership they offer. Equipment to power those networked technologies is also evolving.
PoE offers many benefits to the security industry. It eliminates the need to have a power outlet and low-voltage power supply at every camera location. A single network CAT5 cable can supply both the power to operate the cameras and transmit back the images. The power, in effect, enjoys a "free ride" on the CAT5 cable that is fundamentally required for network connectivity. PoE can reduce the need for multiple power supplies to one common and centralized unit and share a common power backup scheme.
The power sourcing equipment can either be a PoE switch (a network switch that has the PoE feature), or a "mid-span" power source that is located between a regular (non-PoE) Ethernet switch and a PoE network device. This configuration enables networks to accommodate PoE devices without the replacement of an existing Ethernet switch.
The PoE power sourcing equipment will inject power onto the CAT5 cable after interrogating a PoE-powered device - such as a camera - to determine if it is compliant with the standard. Non-compliant devices will be denied power, thus safely restricting operation to intended PoE devices. Altronix offers the NetWay Mid-Span PoE products to provide power over standard network infrastructure, and can accommodate PoE and conventional IP video cameras, as well as edge devices.
Currently, the PoE standard (IEEE 802.2af) accommodates only PoE-powered devices that require less than 13 watts of power. This means that a PoE power source must be capable of sourcing 15 watts to allow for line loss. This power restriction excludes use of numerous camera products that have features including pan-tilt-zoom and infrared illumination. A future standard (IEEE 802.3at) is slated to accommodate up to 25 watt devices, meaning the PoE power sourcing equipment must be capable of supplying 30 watts to allow for line loss.
A non-compliant PoE device that requires less than 13 watts for operation can also be connected to a network by use of a PoE splitter. A splitter is an adapter that presents a PoE authenticating signature from the power supply to the IP device and then splits out the power to a separate 12VDC connection while supplying the non-powered data signal via an RJ45 connector. This configuration, in effect, converts the network device into a virtual PoE-powered device.
The splitter concept can also be applied to enable inclusion of networked devices that require 25 watts. These devices include network cameras that use specific features such as pan-tilt-zoom, IR illumination or heaters/blowers that are not PoE-compliant due to power limitations or models that simply lack PoE connectivity. This type of 25 watt PoE splitter would be considered as "PoE compatible" and is dependent on coupling the splitter with appropriate PoE power source equipment.
Additionally, repeaters can be used to extend PoE length limitations to distances of 100 meters (328 ft.) if the load demand causes unacceptable line drop. The repeater must be designed to be consistent with PoE standards with respect to both the power source equipment and the PoE-powered device.
Proper planning coupled with the right selection of products can enable power systems to fulfill the increasing multitude of requirements for today's complex security and video surveillance products.
