Learn about the contribution of an expert in the industry and in energy supplies, who will delve into a topic of vital importance for the optimal performance of all security systems. By: Paul Rizzuto*
There is a basic operational premise that all security systems must apply, regardless of their complexity and size: if energy falls, nothing works. It's such a simple concept, but the focus on energy supplies is usually overlooked. The fact is that power supplies are the basis for the operation of your system and selecting and installing the right model is a very important decision.
Basic requirements
Low-voltage power is a fundamental requirement for video, access control and fire systems. In their most basic form, power supplies convert incoming AC line voltage into low-voltage AC or DC so that it remains consistent within a range, no matter the type of line, load, or environmental conditions.
Power supplies are available in many shapes and sizes. Some come with or without battery charge for system backup and may include diagnostic features. Specific models designed to meet different standards may have approvals from agencies such as UL, CE, and FM. With so many options, how does one go about selecting the right power supply for an application and what considerations should be taken into account?
Types of energy supplies
There are two types of power supplies available, switching mode and linear mode. There are pros and cons to each type, as described below:
Switching mode supplies: They use a switching regulator that controls the output by varying the "on-off" cycle of power transistor operation.
Advantages
- Highly efficient.
- Less heat dissipation.
- The input voltage range is wider.
- The unit is smaller.
Disadvantages
- EMI and RFI a little higher.
- Slightly higher ripple and output noise.
- Slower transient response.
Switching mode supplies are available in two different versions. The first uses the low voltage output of a separate step downstream transformer as its primary input. The other is an offline design in which the low-voltage transformer is integrated into the power supply board. This design uses primary line voltage 115/20, 50/60Hz input directly to the power supply and eliminates the need to use a standalone low-voltage transformer.
Linear supplies: They use a series regulator in which the power regulator transistor operates in continuous mode, thus supplying a permanent flow of voltage and current.
Advantages
- Continuous flow of current and voltage.
- Reduction of EMI or RFI.
- Less undulation and noise.
- Faster transient response.
Disadvantages
- Lower efficiency.
- Require larger thermal sinks to dissipate heat.
- Precise AC voltage input is critical.
- The unit is larger.
When planning any new video, access or fire system, one of the first and most important considerations is energy demand. This initial determination allows the efficient coupling of the power supply with the system requirements. The same happens when additional devices are added or when an entire system is expanded. With this in mind, a complete overall assessment and calculation of energy demand should be carried out. The following are considerations that must be taken into account based on the magnitude of the project:
1.Mandatory agency approvals and code requirement.
2.Type of devices that require external power.
3.What are the voltage and current requirements of the individual devices and the total system? The commonly used voltage is 12VDC, 24VDC or 24VAC.
To calculate the amount and specifications of the correct power supplies for a system, the following considerations must be taken into account:
a) Number of devices.
b) Outlets protected with fuse or PTC.
c) Dragging of operating voltage and maximum current of the devices.
d) "Standby position" requirements for the battery.
e) Special features (e.g. energy monitoring, fire alarm interface, etc.)
f) Surrounding environment (e.g. operating temperature, humidity, etc.).
g) Line voltage fluctuations.
(h) Energy safety factor.
(i) Internal isolation.
j) Ability to receive burst currents from a panic device.
k) Length of the cable and meter.
(l) Physical characteristics of the power supply (e.g. wall mounting, rack mounting, etc.)
When you have established the need for any of the above items, determine the size of the power supply to ensure reliable system operation. To determine which power supply to use for one or more devices, multiply the current drag of each device to get the total power consumption. For example, an access control system with 16 devices operating at 24VDC with a current drag of 300mA each.
16 (devices) x 300mA (current) = 4.8Amps (total)
It is advisable to increase this result by 20% as a safety factor and thus ensure that sufficient energy is presented.
4.8Amps x 20% = .96Amps (security factor))
4.8Amps + .96Amps = 5.76Amps (total energy required)
Therefore, this access control system requires a power supply of 24VDC and 16 outputs, estimated at 5.76Amps minimum.
Other factors to consider: it requires backup time. Using a calculation tool for the battery will help you to estimate the appropriate battery size.
Location of devices that require power and wiring
To eliminate the possibility of voltage drops, it may be necessary to decentralize the power source based on the distance between the devices and the length and gauge of the cable line. It is important to calculate the appropriate gauge of the cable to be used. To help select the appropriate gauge and calculate the voltage drop over a specific distance, you can use the calculator available on the Altronix website: (www.altronix.com).
Fuses protect electrical devices against current overloads and short circuits. When the current reaches a predetermined magnitude for a fixed period of time, the internal element of the fuse melts and the current flow is interrupted. Fuses are fast and accurate, but they are only useful once.
PTCs (Positive Temperature Coefficient Resistors) function as a circuit breaker. When the current index of the PTC is exceeded, it slowly heats up to reach the temperature threshold, causing a dramatic increase in the resistance opening the circuit. PTCs are temperature-sensitive devices. They travel at currents lower than those specified and at higher temperatures, and currents higher than those specified at lower temperatures. The indices of a PTC can vary +/-50% from the temperature range specified by the manufacturers. The slow and inaccurate response of a PTC can cause damage to delicate electronic devices.
Typical monitoring features may include but not be limited to output power, AC failures, low battery, battery presence monitoring, grounding breakdowns, circuit issues, and fire alarm trigger notification.
The voltage of the line supplying input power can be wired, which requires an expert electrician to make the connection. In some cases, a power supply may incorporate a ground line cable that is simply plugged into a special receptacle for it. Smaller power supplies usually use plug-in transformers.
It can be determined that the power supply board must be installed as a sub-assembly component to provide operational power for a system and/or its complementary devices. In this case, if a UL list is required, the entire system must be submitted for approval. I
An important consideration is the physical and geographical location of energy supplies. This greatly affects the accessibility and serviceability of the units, as extreme environmental conditions can affect performance and operation.
Power supplies are available in a variety of mounting configurations, such as wall, rack and pole. The physical limitations and the design of the system will be the ones that indicate which is the best option.
To achieve future expansion, it is prudent to specify energy supplies with additional outputs and more energy than is currently required.
Knowledge is power
Once all your energy needs have been defined, a good rule of thumb is to increase the power supplies you specify with a margin of 20% as a safety factor and thus ensure optimal system operation 24 hours a day, 7 days a week. Although cost effectiveness is a factor, it should not be the highest priority. Most important considerations should be availability, line breadth, manufacturer tracking record, customer support, and warranty policies.
Unfortunately there are no standards in place when purchasing power supplies that can be applied to all systems or devices. Check with your system designer, system integrator, or manufacturer for advice. If you don't want to have difficulties, make sure your choices have been based on carefully defined parameters.
* Paul Rizzuto is the technical sales manager for Altronix Corp. If you want you can write to the email [email protected]
