Power Options Now in Abundant Supply
A facility manager requests low bids on a security access control upgrade for his building. The lowest bidder provides the manager with the access system controls, card proximity readers and the specified electrified door-locking hardware. After the equipment is installed, the customer complains because the doors will only stay open a second, then relock. The contractor checks his programming and the wiring appears to be fine. The problem still remains.
Another alarm dealer gives a customer a great price on a CCTV system by using state-of-the-art Internet protocol (IP) cameras and power-over-Ethernet (PoE) technology, which is connected into the customer’s existing computer network. Several of the cameras appear not to work right out-of-the-box. The technician moves cameras around, but the problem does not go away. The technician further checks for cabling and termination problems, and all connections check out.
The likely source of these problems is that the system’s power supply equipment was either incorrectly specified and/or misconfigured. Having a better understanding of the types of power supplies used in the security industry can go a long way in reducing a security contractor’s time, money and frustration.
“If the power goes down or is incorrectly specified, it doesn’t really matter how sophisticated your system is — it simply won’t work,” says Alan Forman, president of power supply and security products manufacturer Altronix Corp. of Brooklyn, N.Y.
While security system power supplies can be separated into two types of technology, there have never been more varieties of power supplies to choose from. The entry of more manufacturers into the power supply marketplace is aiding in the increased diversity of supplies and choices for installers.
Linear, Switching Are 2 Basic Types of Power Supplies
There are basically two types of power supply technology.
The most common is the linear power supply. Many are familiar with this technology since it has been around for many years and taught in the technical community.
A linear power supply has a step-down transformer that will reduce typical U.S. line voltage of 120VAC to a lower voltage. This lower AC voltage is then rectified by diode configurations and further filtered by capacitors, inductors and power transistors. This provides clean and consistent power for a variety of security systems.
Linear supplies are typically inexpensive to produce, but they can be heavy in weight and large in size. A rule of thumb for a 16V power supply is one pound of weight for every ampere of current.
Another concern is the heat given off by these power supplies. This is a result of a low efficiency rating of around 50 percent. This can cause problems in having to provide additional cooling in such interior spaces as equipment rooms for access control.
The other type of power supply technology is the switching power supply. These have been around for many years, and one of the most common applications is in the modern-day personal computer.
The switching power supply does not have a step-down transformer input as with the linear power supply. A switching power supply can be fed 120VAC directly, eliminating the transformer. Then, through a high-speed electronic switching process, it delivers a reduced DC voltage. The power supply is around 80- to 90-percent efficient and much smaller in size compared to linear supplies.
If this is such a good power supply, why do we not see more of them?
One reason is that they have typically been more expensive to manufacture. Another downside is that switching power supplies — especially earlier ones — generated noise from their high-speed, high-voltage switching circuits.
We are starting to see more switching supplies as they now have considerably less noise and cost than earlier models (see photo on page 64 of April issue).
Security equipment applications will be determined by how sensitive the equipment being powered is to the noise level of the switching power supply. Check with the equipment manufacturers — it can still make a difference in performance.
More Manufacturers Mean Exciting New Options
In the past, a large percentage of power supplies for the alarm industry were wall-cabinet configurations. Today, companies such as Honeywell Power Products (HPP) provide a variety of power supply configurations. These can be as basic as a small power supply board being installed in other equipment, to a variety of cabinets and transformer combinations.
While this provides many options for the dealer and installer, care should be taken that all National Electrical Code (NEC) and local codes are being followed. Electrical inspectors are often concerned and confused as to how power-supply cabling is configured to share both 120VAC power and Class 2 low-voltage electrical wiring in the same cabinet. It helps to use a power supply that is listed for this cohabitation.
One manufacturer recommends at least a 0.25-inch separation between 120VAC power and power-limited cabling. Also, there is a nonconductive physical barrier between the two circuits in the power supply.
Power supplies designed for large access and CCTV systems now provide intelligent distribution and diagnostic tools. Manufacturers such as Honeywell, Altronix and Alarmsaf provide power supplies with up to 16 to 32 individually fused low-voltage outputs. These panels also provide built-in lightning surge suppression for individual camera power circuits.
Some systems come with either resetable power temperature coefficient (PTC) or fuse protection. The fast speed of fuse protection is recommended over PTC for delicate equipment such as CCTV cameras.
Each power output channel should have an LED indicator to assist in diagnosing and monitoring individual equipment performance. These outputs can be configured with the option of either fail-secure or fail-safe operation in the case of access control. For CCTV, the outputs can provide either AC or DC for camera operation.
Additionally, these power supplies should have a fire alarm control panel interface (FACP). FACP is important in order to drop power to access equipment in the case of a fire, and the National Fire Protection Association (NFPA) requires it.
Many of today’s power supplies also allow for the control of the voltage level of the power supply output. A common selection is either 12 or 24VDC outputs. This not only allows the matching of the voltage level of components being installed, but also helps the experienced technician compensate for other technical issues.
The demand and interest in power supplies has grown to the point where some major manufacturers have added them to their product lines in order to better serve their networks of installing alarm dealers and systems integrators. For example, NAPCO Security now offers power supplies to complement its security and access control products and systems, while Pelco has done the same for its line of CCTV devices and solutions.
Changes in the alarm industry’s performance requirements for power supplies within the past year also stand to benefit installers.
“Industry standards such as UL 864 Ninth Edition require a significant performance improvement. Additional features, once optional, have become required,” says Joe Holland, vice president of engineering for Alarmsaf. “NFPA 730 and 731 will require features such as these that exist in the fire industry to be implemented within the access control industry. This is definitely a time of change for the power supply manufacturers.”
Be Sure to Compensate for Security Circuit Voltage Drop
Technically savvy security contractors realize that any electrical device being powered by a power supply has to account for the configuration of the complete circuit. This would include the
wire or cable coming from the power supply to the particular device, such as a CCTV camera, motion detector or electrified door lock. Understanding the relationship of electrical voltage (current and resistance as set forward in the Ohm’s Law formula: E = IR), it is understood that, depending on the load of a the circuit, a considerable amount of voltage needed by the security device may be stolen or “dropped” across resistance of the cable, rather than the security device.
What does that mean in layman’s terms? It means there won’t be enough power to make the security device work properly. This could have been the reason for the problems at the beginning of this article.
Typically, 24V security devices require less current to operate than 12V devices.
This will cause less current going through the cable and less voltage drop on the length of cable during those long high-resistance runs. In many cases, manufacturers will have some tools to help calculate this power cable voltage drop when designing a system.
Problems from cable voltage drops can occur even in the newer PoE applications. One of the key restrictions with the current PoE IEEE 802.3af standard is the limitation of 100 meters. This is due to the low wattage available for devices such as CCTV cameras.
By having too long of a cable run, one could have too much of a voltage drop and, consequently, have a problem similar to the one described with the CCTV cameras at the beginning of this article.
When dealing with these power supply and voltage-drop issues, an alarm technician can move the location of the power supply. In the past, many contractors and integrators have had trouble with centrally delivering the correct power needed for trouble-free access door control. To compensate for this, electrified panic hardware manufacturers such as Von Duprin recommend matching their door hardware with a Von Duprinspecified power supply.
Additionally, the matched power supply and battery should be specified and installed in the immediate area of the electrified panic hardware. Less cable length, less voltage drop. Using a power supply that is designed for the door hardware and having it close to the access door will correctly compensate for the exit device’s operational high-current surge demand.
Rack-Mounted Supplies Growing in Market Power
With the increase in networked systems and PoE systems integration, rack-mounted power supplies are growing in popularity. Each power supply manufacturer at the recent ISC West show in Las Vegas had its latest models on display.
For example, the “hot swappable” PoE modules from Belden/CDT allow for replacement of a defective port without having to bring the entire rack offline.
“The Belden products are all hotswap modular PoE products,” says Mike Posey, a consulting engineer for the cabling manufacturer. “The PoE ports are on plug-in modules that can be replaced rapidly in the field for troubleshooting, expansion or repair. Nonmodular products have to be unscrewed from the rack and replaced as a unit – even if only one of 24 ports has failed.”
Manufacturers are making exciting new product announcements in the area of PoE technology (see “Power Over” sidebar on page 64), and everyone is excited about with these new applications.
While various power/signal over UTP/coax products have been around for sometime, manufacturers like Altronix are taking a new direction with products such as the Hub- Way product line. This is a power supply designed to provide centralized UTP video, RS422/S485 data and distributed camera power over a single Cat-5, -5e and -6 cable
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