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2018-07-27
www.myddisplay.com

Regarding the problem of display power consumption and cable cross-sectional area, we will explain this knowledge for you. We calculate the electricity consumption of an electrical product, which is calculated by its electric power, that is, how much "work" the electric appliance makes per hour and this work is obtained by multiplying the current by the voltage.

However, in general calculation of power load is divided into two types in actual use, one type of resistive load and another type of inductive load.

For the calculation of resistive load: P = UI, ie power = voltage × current

For the calculation of the inductive load: P = UIcosф, ie power = voltage × current × power factor.

And our **LED display** is used by transformer switching power supply, which is an inductive load. The power factor of its switching power supply load is cosф = 0.75. Different inductive load power factors are different. When we calculate the LED display power supply switching power supply, we can take the power factor cosφ to 0.8.

The LED display drive voltage is 5V, and the drive current is less than 20mA. The maximum power calculation method of the screen is as follows (based on 100 square meters):

1. The specifications of the **outdoor LED display** are: the pixel pitch is 10mm, the dot density is 10000 points/square meter, and each point (pixel) is composed of 1 red 1 green 1 blue 3 LED lamps, and the scanning mode is 1/4 scan.

2. The display power per square meter display: P = 10000 (point) X (particles) X 5 (volts) X 0.02 (A) X 1/4 (scan) = 750 (Watts)

3. The display screen body full screen power consumption: P = 750 (watts) X100 (square meters) = 75KW

4. Full screen power consumption:As the loss which the power is converted between products, the general power is increased by 10% based on the theoretical calculation value. The auxiliary equipment (air conditioner, fan, lighting, power amplifier, etc.) also generates a certain amount of power consumption.The power consumption of the auxiliary equipment of this screen is calculated according to the actual amount (we calculate the following formula temporarily calculated according to 5KW).

P= 75KW+7.5 KW +5KW =87.5KW

So the total display power is 87,500 watts, then the maximum current is:

I=P/Ucosф=87500（watts）÷220*0.8（cosф）=318(A)

However, under normal working conditions, the display LED cannot be lit for a long time at the same time.Therefore, the user's power supply capacity is small, and a common coefficient formula can be used, and the common coefficient is generally 0.5.

Therefore, the above calculation should be rewritten as:

I=P*Common coefficient/Ucosф=(82500(Watts)*0.5+5000(Watts))÷220*0.8(cosф)=168(A)

In other words, the total current value of this screen is 168A. As the instantaneous current of the LED display is relatively large, the total air switch can not use the three-phase 168A switch,should use the air switch of 318A , and select 400A. Many of our peer engineers are accustomed to directly calculate the total power of the large screen by the number of switching power supplies on the whole screen,which method is not standard. Some manufacturers reduce the number of switching power supplies in order to reduce costs, and finally lead to incorrect power calculation.

5. Average power consumption: As the playback content is different and the power consumption is different. For example, if you play commercials, the colors are rich and the white is mostly. The average power consumption is 50% of the maximum power consumption. When playing simple graphics such as text, most of the screens are black, and the average power consumption is 10% of the maximum power consumption. According to normal advertising statistics, the average power consumption is 40% of the maximum power consumption.

The general copper wire safety calculation method is:

The safe current carrying capacity of the 2.5 square millimeter copper power cord --28A.

The safe current carrying capacity of the 4 square millimeter copper power cord - 35A.

The safe current carrying capacity of the 6 square millimeter copper power cord - 48A.

The safe current carrying capacity of the 10 square millimeter copper power cord - 65A.

The safe current carrying capacity of the 16 square millimeter copper power cord - 91A.

The safe current carrying capacity of the 25 square millimeter copper power cord - 120A.

If it is an aluminum wire, the wire diameter should be 1.5-2 times that of the copper wire.

If the copper current is less than 28A, it is safe to take 10A per square millimeter.

If the copper current is greater than 120A, take it at 5A per square millimeter.

In addition, if the copper wire of 6 square millimeters or less is used indoors, it is safe to use no more than 10A per square current. From this point of view, you can choose 1.5 square millimeters copper wire or 2.5 square millimeters aluminum wire.

If the power supply distance is within 10 meters, the wire current density of 6 A/mm 2 is suitable, 10-50 m, 3 A/mm 2 , 50-200 m, 2 A/mm 2 , and less than 1 A/mm 2 over 500 m. From this perspective, if not very far, you can choose 4 square copper wire or 6 square aluminum wire.

If the power supply distance is 150 meters, 4 square millimeters copper wire must be used.

The impedance of a wire is proportional to its length and inversely proportional to its wire diameter. When using the power supply, pay more attention to the wire material and wire diameter of the input and output wires to prevent the current from being excessive and causing the wire to overheat and cause an accident.

Below is a table of wire diameters and maximum currents that copper wire can be withstood at different temperatures.

Wire diameter (Approximate value)（mm2) |
Copper wire temperature（℃） |
|||

60 | 75 | 80 | 90 | |

2.5 |
20 |
20 |
25 |
25 |

4.0 |
25 |
25 |
30 | 30 |

6.0 |
30 |
35 |
40 | 40 |

8.0 |
40 |
50 |
55 | 55 |

14.0 |
55 |
65 | 70 | 75 |

22.0 |
70 |
85 | 95 | 95 |

30.0 |
85 |
100 | 100 | 110 |

38.0 |
95 |
115 |
125 | 130 |

50.0 |
110 |
130 | 145 | 150 |

60.0 |
125 |
150 | 165 | 170 |

70.0 |
145 |
175 |
190 | 195 |

80.0 |
165 |
200 | 215 | 225 |

100.0 |
195 |
230 | 250 | 260 |

The wire diameter is generally calculated as follows:

Copper wire: S= IL / 54.4*U`

Aluminum wire: S= IL / 34*U`

Explanation: I——maximum current passing through the wire (A)

L——the length of the wire (M)

U`——allowed power drop (V)

S——cross-sectional area of the wire (mm2)

If the wiring of the cable is too long, or the high temperature environment, or the concealed laying requires a cumulative discount calculation, it will affect the normal use and make the cable hot. In addition, it is recommended that the air-opening without the grading power-on is replaced every five years. Because of frequent switching, the current causes the aging of the electric shock, which makes the open contact poor. The above two items are not taken seriously causing serious fires.