In our country, most communication power supplies use -48V power supply. As a communicator, do you know why?

Before solving this question, let‘s first understand where the -48V power supply comes from!

 

█ How is -48V power generated?

The power supply for communication equipment can be AC ​​power or DC power.

To achieve uninterrupted power supply, in addition to UPS (Uninterruptible Power Supply, uninterruptible power supply), we must rely on the power stored in batteries. The monitoring module is responsible for the management of the entire system and transmits data to the remote monitoring terminal.

The picture below takes the mains power as an example to introduce the working structure of the communication power supply system.

As can be seen from the picture above , the -48V power supply is converted from alternating current or high-voltage direct current through a rectifier module .

 

█Why use -48V power supply?

Seeing this, many people will ask:

Why is the power supply voltage -48V?

Why is it -48V, not +48V?

What is the difference between -48V and +48V?

 

QUESTION. 0 1

Why is the power supply voltage -48V?

Why does the communication power supply use -48V voltage? In fact, this reason mainly comes from the following aspects:

 

1 Historical reasons :

Most of the earliest communication equipment used in history, such as telephones, were powered by -48 V voltage, and the communication power supply was supplied by the telecommunications bureau.

 

2 safety factors :

Internationally, the DC voltage of -36V is defined as a safe voltage. -48V is slightly higher than the safe voltage, and the voltage drop of the line will be smaller. Under safe conditions, long communication distance for local calls is ensured.

With the continuous development and progress of information technology, in order to be compatible with early equipment and reduce costs, -48V power supply has been used until now.

 

3 Reduce losses :

It is conducive to the transmission of electricity and can reduce the loss of power supply materials.

High voltage is more dangerous to use than low voltage. For low-voltage transmission, because the current on the load line of the same power is too large, the line resistance needs to be reduced, so thicker power lines must be selected, which will increase line costs and may also affect the normal operation of the communication system.

 

 

QUESTION. 0 2

Why -48V instead of +48V?

 

 

The use of -48V is mainly due to the electrochemical characteristics of the transmission line medium of communication equipment. The polarity of -48V is negative, that is, the positive electrode is grounded.

This is because communication equipment uses DC power supply, and there is humidity in the air, which causes the positive electrode of the equipment to be electrolytically corroded by the electrolysis of DC power.

Grounding the positive electrode of the power supply equipment can absorb a large amount of negative charges in the air, reduce the corrosion of the positive electrode of the power supply equipment, and thereby protect the outer casing of the power supply equipment from rust.

 

QUESTION. 0 3

What is the difference between -48V and +48V?

 

 

The voltages of -48V and +48V are equal, the difference lies in the direction of the current .

Negative voltage is used because electrons are negatively charged and will flow in the direction of positive voltage, thereby preventing too many electrons from gathering on communication equipment, thereby reducing the failure rate of communication equipment.

 

Off-topic extension

-48V Do you understand? ! So what is -53.5V?

53.5V is the float charge voltage . In daily power supply, the power supply needs to float charge the battery, so the actual measured voltage is -53.5V.

 

█Supplementary instructions

Although China‘s communication power supply uses -48V power supply system, not all countries use -48V power supply system . For example, Russia will use a -60V power supply system, and some countries use a -24V power supply system.

Therefore, if the product is to be promoted to other areas with different power supply systems, the communication power supply standards of these areas must be taken into consideration.

 

Optic network data transmission DWDM OTN Solution, any need solution design and cost quotation, pls feel free to link with me via below info.