1.The importance of video access control power supply selection

There is no doubt that the power supply is the basis for ensuring the stable operation of the whole video access control system. The selection of the power supply can directly determine whether the engineering company can earn as much profit as possible when implementing the project. At the same time, the selection of the power supply can also reflect the engineering company's ability to control the quality of the project.

Unfortunately, when the author investigated the macro market of the whole video access control system, it was found that more than 90 system failures were caused by the improper choice of power supply, and some failures may have affected the smooth promotion of the project. In summary, the fault caused by the power supply is mainly manifested in the following aspects:

① After a period of use, the power supply is insufficient.

② Power failures occurred on the scale after a thunderstorm.

③ Power failure occurs in hot and cold weather.

④ The battery is often bad, and does not play a power cut to maintain the normal operation of the system.

⑤ The power supply is burned out due to short circuit.

⑥ Power consumption peak, there is insufficient power supply problem.

2. Application and selection of power supply in video access control alarm system

(1)Measure the actual power output

(2)Effective lightning protection

(3) Wide temperature adaptation range

(4) Intelligent charge and discharge management for backup batteries

(5) fault isolation, avoid individual equipment damage and affect the global stability of the system

(6) Wide voltage range, stable power output

(7) The choice of switching power supply and linear power supply

(1)Measure the actual power output

There are many devices to be powered in video access control alarm system. In order to ensure the normal and stable operation of each device, the power supply needs to have enough power to power each device. When purchasing power supply, we should pay special attention to the nominal value of the power supply, and for the actual parameters, it is best to field test, because there are some cheap access control power supply on the market in practical application often cannot reach the nominal value, which seriously affects the normal and stable operation of the video access control alarm system. You are advised to select a power supply manufacturer that meets the technical specifications, is reliable in quality, has a good reputation, and is suitable for the video access control alarm system. At present, some video access control manufacturers, the power supply is sold together with the controller, usually this kind of manufacturers for the choice of power is to consider the actual application of the project, for the overall quality of the system also has a better guarantee, such as Shenzhen's S4A brand.

Simple method to test the output power of the power supply: add a load corresponding to the output power of the power supply (such as cement resistance), run for more than 48 hours, use a multimeter to measure the actual output voltage and current of the power supply, and compare with the nominal value, in order to test whether the output voltage is stable after adding the load? Is the calorific value normal? Conditions can be the best field installation trial run.

(2)Effective lightning protection

Because of the particularity of the video access control alarm system project, the installation environment is harsh (farmer's house, rental house, old house village, village in the city), the outdoor lines are interwoven, easy to mine, and the power connected line inevitably appears in the outdoor, so the power should have strong effective protection measures for lightning protection.

Judgment of whether the product has lightning protection:

① Visually test whether there is a protective circuit design on the power supply. (This method is suitable for circuit hardware research).

② Understand whether the manufacturer has accumulated technology in lightning protection technology, such as the actual demonstration of product reliability. Related products lightning detection report and so on.

(3) Wide temperature adaptation range

At present, the installation of video access guard, the southernmost Shenzhen is famous for its hot, the northernmost Urumqi is famous for its cold. If the product does not have a wide range of high and low temperature adaptation, the reliability of the system is not guaranteed, especially the power supply part, so the choice of products should be based on their installation environment to choose.

Generally speaking, the temperature adaptation range in -40 degrees - 85 degrees, can meet the requirements.

Specific testing methods can be required to cooperate with manufacturers to provide, or in the quality assurance can be clear in the contract terms to ensure their legitimate rights and interests.

(4) Intelligent charge and discharge management for backup batteries

Because of the special environment of the rental house or the community, the mains power outage occurs from time to time, and the video access control, especially the access control in the middle, is directly related to the life of the people, requiring normal operation at any time, so generally around the construction of video access control specifications for the battery life of the backup will put forward specific requirements, It is required to maintain the normal operation of the system for more than 4-6 hours after power failure. The power supply has the charge and discharge management function.

The charge and discharge management function of the power supply is mainly to avoid damage to the battery by overcharging the battery, and it will not be recharged after excessive discharge because the charging current is too large and pull down the current supply of other equipment, resulting in system instability.

Supplement: Compared with the access control system, the power consumption of the video system is relatively large, and does not affect the direct opening and closing of the door, so in the actual construction of the power supply after power off, many engineers choose to ensure the power supply of the access control system after power off. At present, some power supply products have the function of mains power failure detection. After power failure, the power supply of the video system is cut off, so as to ensure that the battery as small as possible is used to ensure the longer power supply life of the access control system, which really saves the construction investment of the engineering company on the backup battery.

(5) fault isolation, avoid individual equipment damage and affect the global stability of the system

Due to the diversity of hardware equipment of video access control alarm system, it is bound to involve one power supply for multiple devices. At this time, it is necessary to pay attention to the independent power supply output of the selected power supply with multiple output terminals, and it is required that the power supply can judge the output current intelligently. In this way, when one power supply line is centralized or the output of one power line is faulty, the output of other power lines will not be affected. Even if the output of one power line is directly short-circuited, the output of other ports will not be affected. Of course, the power supply can't be burned out by a short circuit in one port.

(6) Wide voltage range, stable power output

Mains voltage fluctuation often occurs, or high, or low. Therefore, the power supply must be able to adapt to the mains voltage fluctuations in a wide range, and the output voltage can be stably output at 12V to avoid the unstable power supply caused by the mains voltage fluctuations, which will affect the normal and stable operation of the video access control alarm system.

(7) The choice of switching power supply and linear power supply

In the actual project application, whether to choose switching power supply or linear power supply, many engineering friends do not know how to start, in fact, as long as the two points can be grasped:

① In the hot areas of the south, if the linear power supply is selected, it is recommended not to put the linear power supply and other equipment in the same equipment box, because the linear power loss is large, the heat is very severe, and other equipment in an equipment box, if the heat dissipation is not timely, it is likely to cause the operation of other equipment is unstable. And if the linear power supply with a dedicated box, it will bring some cost increases.

② Low-cost linear power supply generally does not have battery charge and discharge management function, it is easy to cause damage to the battery.

Author:Written by Ms.Rebecca Fu from S4A INDUSTRIAL CO.,LIMITED