华为通信电源为什么都是－48V的？

小常识：为什么通信电源都是－48V的？ 

为什么通信电源电压是-48V? 

       通信电源其实用过多种：老式的机电式交换机，如步进制、纵横制式，都是-60V；载波室内电子管要求-24V(灯丝和继电器等电源、晶体管载波机工作电源)和+130V(阳极电

源)。  

       通信设备中应用大量继电器等元件，使用直流工作电源。空气中的湿度总是存在的，在直流电的电解作用下，总是正极受到电解腐蚀。如果工作电源是+48V，继电器等设备的铁芯接机架，线圈通电，受到腐蚀的将是线径很细的线圈，故障率会比较高；采用电源正极接地(机架)，线圈工作电源是负电压，受到腐蚀的将是体积很大的铁芯，故障率会大大

下降。所以都是采用正极接地方式，用负电压电源。 

       为了简化电源设备，现在的程控交换机、光端机等设备，都是用-48V电源。因为程控交换机与电话在用户的距离比较远，为了保证一定的服务范围，交换机的电源电压不能过低，所以通信设备统一使用-48V电源。在用户小交换机设备上，交换机与电话机的距

离很近，一般是采用-24V电源，不用-48V。 

电话的技术水平是一步步的发展的，从手摇的磁石式电话到共电式电话，一直到程控电话。 在发展的过程中，不同种类的技术，有一个过渡阶段，就存在一个兼容的过程。好比出现了彩色电视以后，黑白电视机也能够收视彩色信号的节目，所以彩电技术的发展，不能完全抛开黑白电视的广大观众，彩电技术中的黑白信号，和原来的黑白电视有一定的共通之处。 

       共电式电话的电源电压就是48伏，所以在发展程控电话的时候，也就采用了这

一个电压等级，以求得和共电式电话的兼容，这样做也不会影响新技术的发展。 如果以后会出现更先进的有线电话，估计还是会采用48伏的电压。另外：他可以防止电化

学腐蚀；防雷击；加强屏蔽等功能 

       从华为的资料中找到为什么是正极接地的解释，作为补充解释： 正极接地主要是为了防止电极的腐蚀。电话局蓄电池组-48V或-24V是正极接地，其原因是减少由于继电器或电缆金属外皮绝缘不良时产生的电蚀作用，使继电器和电缆金属外皮受到损坏。因为在电蚀时，金属离子在化学反应下是由正极向负极移动的。继电器线圈和铁芯之间的绝缘不良，就有小电流流过，电池组负极接地时，线圈的导线有可能蚀断。反之，如电池组正极接地，虽然铁芯也会受到电蚀，但线圈的导线不会腐蚀，铁芯的质量较大，不会招致可察觉的后果。正极接地也可以使外线电缆的芯线在绝缘不良时免受腐蚀。（注：隐含条

件是继电器铁芯接地）最好能有个接线图就更清楚了。

Why are HUAWEI communication power all - 48?

Common sense: Why are communication power sources - 48? It

Why is the communication power voltage -48V?

It

There are many kinds of power supply for communication: old-fashioned electromechanical switches, such as step-by-step, vertical and horizontal, are all - 60V; Carrier room tube requirements - 24V (filament and relay power supply, transistor carrier operating power supply) and + 130V (anode power supply)

Source). Such

A large number of relays and other components are used in communication equipment, and the DC power supply is used. Humidity always exists in the air. Under the action of direct current electrolysis, the positive electrode is always corroded by electrolysis. If the working power supply is + 48V, relay and other equipment, the iron core rack, the coil is electrified, the corrosion will be very small coil diameter, the failure rate will be higher; the use of power positive grounding (rack), coil power supply is negative voltage, corrosion will be a large volume of iron core, the failure rate will be large

Drop. So they all adopt positive pole grounding mode and use negative voltage power supply. It

It

In order to simplify the power supply equipment, the program-controlled switches and optical terminals are all powered by - 48V. Because the distance between SPC switchboard and telephone is relatively far from the user, in order to ensure a certain range of service, the power supply voltage of the switch can not be too low, so the communication equipment unified use - 48V power supply. The distance between the switch and the telephone on the PBX device.

Very close, generally using -24V power, not -48V. It

The technical level of the telephone is a step-by-step development, from the hand-rocked magnet phone to the common-purpose telephone, to the program-controlled telephone. In the process of development, different kinds of technology, there is a transitional stage, there is a compatible process. For example, after the appearance of color TV, black-and-white television can also watch color signal programs, so the development of color TV technology, can not completely throw away the black-and-white television audience, color TV technology in black and white signals, and the original black and white television has some similarities. It

It

The power supply voltage of the uuuuuuuuuuuuuuuuuuuuuuu

A voltage level to be compatible with a common telephone does not affect the development of new technologies. If there will be more advanced wire telephone in the future, it is estimated that the voltage will still be 48 volts. In addition, he can prevent electrification.

Learn corrosion, lightning protection, strengthen shielding and other functions.

I am very sorry.

From Huawei's data, we can find the explanation why positive grounding is. As a supplementary explanation, positive grounding is mainly to prevent electrode corrosion. Telephone office batteries - 48V or - 24V are positively grounded due to the reduction of corrosion due to poor insulation of the metal skin of relays or cables, resulting in damage to the metal skin of relays and cables. Because during corrosion, metal ions move from the positive electrode to the negative electrode under the chemical reaction. If the insulation between the relay coil and the iron core is poor, a small current will flow through the coil. When the negative electrode of the battery pack is grounded, the conductor of the coil may be broken. On the contrary, if the positive electrode of the battery pack is grounded, although the iron core will be corroded, the conductor of the coil will not be corroded, and the iron core will be of high quality, which will not cause noticeable consequences. Positive earthing can also make the core wire of external cables avoid corrosion when insulation is bad. (Note: implied clause

The relay is the core of the relay. It is better to have a wiring diagram.

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