1. The role of valve-regulated sealed lead-acid batteries in communication
power systems
1. Backup power supply, including DC power supply system and UpS system
2. Filtering
3. Adjust system voltage
4. Power equipment starting power
Figure 1: Schematic diagram of battery function
2. Types of stationary lead-acid batteries
Acid-proof explosion-proof battery (GF or GFD battery)
Stationary lead-acid battery
AGM—cathode absorption type (lean liquid type)
Valve regulated sealed battery (VRLA battery)
GEL—colloidal type
1. Compared with GF batteries, VRLA batteries have the following
characteristics:
(1) During use, there is no need to add water or adjust the acid ratio.
(2) No leakage, no acid mist, and no environmental pollution.
(3) Small self-discharge.
(4) Compact structure, good sealing, earthquake resistance, and high
specific energy.
(5) There is no memory effect.
(6) Wide range of use.
Figure 2: Comparison of VRLA batteries and GF batteries (left)
2. Comparison between cathode absorption VRLA batteries and gel
batteries:
(1) There is no gas escaping from the AGM battery in the early stage of
use, while the GEL battery needs to be equipped with an exhaust device in the
early stage of use.
(2) AGM batteries have small internal resistance and have better
high-current discharge characteristics than GEL batteries.
(3) The consistency and uniformity of AGM batteries are better because the
diffusivity and uniformity of the electrolyte are better than those of GEL
batteries.
(4) GEL batteries (especially tubular electrodes) have a long service life
and are not prone to thermal runaway.
3. Working principle of VRLA battery
1. Battery charging/discharging principle:
The basic electrode reaction of lead-acid batteries is the conversion
between lead (pb) and divalent lead (pb2+) and tetravalent lead (pb4+).
Discharge process: negative electrode: pb→pb2+ positive electrode:
pb4+→pb2+ (
(+) pbO2+3H++HSO4-+2e put <═══> to charge pbSO4+2H2
Electron gain and loss are: negative loss and positive gain, that is,
negative oxidation and positive reduction.
Charging process: negative electrode: pb2+→pb positive electrode:
pb2+→pb4+
(-) pb+HSO4-Put <═══> charge pbSO4+H++2e
Electron gain and loss are: negative gain and positive loss, that is,
negative reduction and positive oxidation.
Battery charge and discharge reaction
The total reaction of the battery: pb+2H++2HSO4—+pbO2, put <═══> and
charge pbSO4+2H2O+pbSO4
2. Sealing principle of VRLA battery:
(1) Causes of gas generation inside the battery:
When the battery is overcharged, the battery decomposes water, producing O2
at the positive electrode and H2 at the negative electrode.
H2 is produced when the positive grid corrodes
When the battery self-discharges, the positive electrode produces O2 and
the negative electrode produces H2
(2) Oxygen recombination principle (oxygen cycle principle):
During the charging process of the battery, in addition to the
transformation of pbSO4 into pbO2 at the positive electrode, there is also an
oxygen evolution reaction. Especially in the late charging period of the
battery, when the battery capacity reaches 80%, the oxygen evolution reaction is
more severe. The gas evolution reactions at the two poles are as follows. :
(+)2H2O→O2+4H++4e(--)2H++2e→H2
For VRLA batteries used for float charging, even if the float charge
current is very small, in the long-term float charge state, except that part of
the float charge current is used to convert pbSO4 generated by battery
self-discharge into positive and negative active materials, it is unavoidable.
The other part of the floating charge current is used for the electrolysis of
water, so that oxygen is released from the positive electrode and hydrogen is
released from the negative electrode.
The generation of oxygen and hydrogen causes water loss inside the battery,
changes the density of the electrolyte, and also makes the battery difficult to
seal. Since the birth of lead-acid batteries, people have been seeking to seal
the batteries to reduce battery maintenance. The emergence of VRLA batteries
realizes the sealing of batteries. The key technology of battery sealing is the
recombination of oxygen inside the battery to achieve oxygen circulation, and
the use of AGM separators to absorb electrolyte so that there is no flowing
electrolyte inside the battery and the recombination of oxygen The principle is
shown in Figures 3 and 4:
Figure 3: Schematic diagram of sealing principle
Figure 4: Oxygen cycle schematic diagram
As can be seen from Figures 3 and 4, the oxygen released from electrolyzed
water during the charging process of the positive electrode quickly diffuses to
the negative electrode through the pores of the AGM separator, reacts with the
sponge-like lead, the negative electrode active material, to form lead oxide
(pbO), and the surface of the negative electrode When pbO meets the electrolyte
H2SO4, a chemical reaction occurs to generate pbSO4 and H2O. pbSO4 is recharged
and transformed into sponge-like pb. The generated H2O returns to the
electrolyte. Due to the recombination of oxygen, the loss of water is avoided,
thus realizing the battery of seal.
Measures to achieve sealing of lead-acid batteries:
1) Choose high-porosity AGM separators with a porosity of more than 93% to
provide channels for oxygen recombination.
2) Adopt quantitative acid filling so that after the glass wool separator
absorbs the electrolyte, there is still 5-10% porosity that has not been filled
with electrolyte. Therefore, VRLA batteries are also called liquid-poor
batteries.
3) Excessive negative active material. The capacity ratio of positive and
negative plates is generally 1:1.1~1:1.2. In this way, after the positive
electrode is fully charged, the negative electrode is not fully charged to
prevent hydrogen from being precipitated at the negative electrode. If a large
amount of hydrogen is precipitated, it is Cannot be compounded.
4) For the tight assembly of the battery cluster, cluster pre-compression
technology is adopted to press the assembly between 40-60Kpa to ensure good
contact between the AGM separator and the surface of the positive and negative
plates, because the electrolyte of the VRLA battery mainly relies on the AGM
separator. supply.
5) High-purity pb-Ca-Sn-Al antimony-free grid alloy, because pb-Ca alloy
has a higher hydrogen evolution overpotential than pb-Sb alloy, which can reduce
the possibility of hydrogen evolution due to grid corrosion.
6) A safety valve with stable and reliable opening and closing valve
pressure. The standard for VRLA batteries for communication requires the opening
pressure to be 10-35Kpa and the closing pressure to be 3-15Kpa. The opening and
closing valve pressures are relatively close, which can reduce gas emissions and
water loss.
7) Using constant voltage and current limiting charging method, VRLA
batteries are more sensitive to overcharging, which will accelerate current
damage. Constant voltage and current limiting charging can prevent overcharging
and thermal runaway.
3. Self-discharge principle of VRLA battery:
Reasons for battery self-discharge:
1) The reaction between the positive active material and the
electrolyte;
2) The reaction between the positive active material and the grid
alloy;
3) The reaction between the positive electrode active material and the
negative electrode to release hydrogen gas.
Four. Two major categories of VRLA battery technologies
Applying the same oxygen recombination principle, but using different fixed
electrolyte technology and different oxygen recombination channel technology, it
can be divided into two major types of VRLA batteries, namely AGM technology and
GEL technology (colloid), so it is also called AGM Batteries and gel batteries.
Both types of batteries have their own advantages and disadvantages. Currently,
AGM batteries are still mainly used in telecommunications, power and other
markets.
1. AGM technology
For VRLA batteries using AGM technology, the AGM separator adopts U-shaped
coating method (S-shaped coating method can also be used). The characteristics
of VRLA batteries using AGM technology: small internal resistance, using
ultra-fine glass wool separators to absorb the electrolyte, so that there is no
electrolyte in the battery. The AGM separators have a porosity of more than 93%,
and about 10% of the pores are used as The O2 precipitated from the positive
electrode is recombined with the negative electrode to realize the circulation
of oxygen and achieve the purpose of battery sealing.
2. Gel technology (colloid technology)
The OpZV gel battery produced by German Sunshine Company using Gel
technology is a typical representative.
The characteristics of the gel battery: the internal resistance is large,
and the thixotropic SiO2 colloid is used to absorb the electrolyte so that the
electrolyte does not flow.
Composite channel of O2 with colloid microcracks. In the early stages of
use of the gel battery, the colloid failed to form a large number of
microcracks, and the recombination efficiency of oxygen was low.
5. Failure modes of VRLA batteries
Despite its many advantages, VRLA batteries, like all batteries, have
reliability and longevity issues. VRL battery literature reports: its service
life is about 15 years (floating charge at 25°C). However, VRLA batteries at
home and abroad have experienced premature failure during actual use. The
current failure modes of VRLA batteries mainly include corrosion and growth of
the grid, drying up of the electrolyte, sulfation of the negative electrode,
early capacity loss (pCL), thermal runaway, etc.
6. Use and maintenance of VLRA batteries
1. Selection of VLRA batteries
The VLRA battery model must be correctly selected before use to ensure that
the battery has sufficient discharge capacity so that communication equipment
can operate normally; in addition, choosing a reasonable capacity can avoid
waste caused by selecting too large a capacity.
There are two selection methods: 1) calculation method 2) and curve search
method.
2. Installation, use and precautions of VLRA batteries
Before installing and using the battery, you should first read the product
manual carefully and install and use it as required. When installing, special
attention should be paid to the following aspects:
1) The installation plan should be formulated according to the location and
conditions, such as ground load, ventilation environment, sunlight exposure,
corrosion and organic solvents, machine room layout, convenience for
maintenance, etc.
2) New and old batteries generally cannot be mixed during installation, and
batteries of different types or batteries with different capacities must not be
mixed.
3) Batteries are all 100% charged before leaving the factory. They must be
handled with care to avoid short circuits. Insulated tools and insulating gloves
should be used during installation to prevent electric shock.
4) Before installation and use, the battery should be stored in an
environment of 0 to 35°C. The storage period is 3 months. If it exceeds 3
months, the battery should be recharged according to the standards given in the
instruction manual.
5) According to the specified series and parallel lines, connect the
batteries between columns, between layers, and panel terminals. Before
installing the terminal connector and turning on the entire power system, you
should carefully check the positive and negative polarities and measure the
system voltage. And note: on the premise of complying with the design
cross-sectional area, the lead wire should be as short as possible to reduce the
voltage drop during large current discharge; when more than two groups of
batteries are connected in parallel, the cables from each group of batteries to
the load should be of equal length to ensure It is beneficial to balance the
current of each group of batteries when charging and discharging the
battery.
6) When connecting the battery, the screws must be tightened, but excessive
tightening force must also be prevented from damaging the copper-embedded
poles.
7) After installation, the system voltage and the positive and negative
polarity directions of the battery should be checked again to ensure that the
battery is installed correctly.
8) Use a soft cloth soaked in soapy water to clean the battery case, cover,
panel and connecting wires. Do not use organic solvents to avoid corrosion of
the battery cover and other components.
3. Maintenance of VRLA batteries
1) Installation of valve-regulated sealed lead-acid batteries
Valve-regulated sealed lead-acid batteries do not need to have a dedicated
battery room and can be installed in the same room as communication equipment.
Can be stacked or mounted on a rack.
2) Items to be checked frequently
a. Float voltage, ambient temperature;
b. Is there any looseness or corrosion at the connection?
c. Whether the battery case is leaking or deformed;
d. Whether there is acid mist overflowing around the pole and safety
valve;
3), supplementary electricity
a. After the battery system is installed, recharge the battery pack;
b. The battery has been left unused for more than three months;
battery discharge
a. A verification discharge test should be conducted every year based on
the actual load, and 30%-40% of the rated capacity should be discharged;
b. Do a capacity test every three years, and once a year after six years of
use;
4) Measurement of battery capacity
Method 1: Offline measurement method
a. After fully charging the battery pack separated from the power supply
system, let it stand for 1-24 hours, and then start discharging when the ambient
temperature is 25℃±5℃;
b. The terminal voltage of the battery should be measured before the start
of discharge. The discharge current, time and ambient temperature of the battery
should be measured during discharge. The fluctuation of the discharge current
should not exceed 1% of the specified value;
c. During the discharge period, the battery terminal voltage and room
temperature should be measured. The measurement time intervals are: 10h rate
discharge for 1 hour, 3h rate discharge for 0.5h, 1h rate discharge for 10
minutes. Measurements should be made at any time at the end of the discharge
period to accurately determine the time to reach the discharge end voltage.
;
d. The discharge current multiplied by the discharge time is the capacity
of the battery pack. When the battery is not discharged at a 10-hour rate or the
environment
When the temperature is not 25℃, the actual measured capacity should be
converted into the capacity at 25℃;
e. After the discharge is completed, the battery pack must be charged. The
charged capacity should be 1.2 times the discharged capacity.
Method 2: Online measurement method
a. In the power supply system, turn off the rectifier and let the battery
pack discharge to supply the communication equipment. When the battery pack is
discharging, find the battery with the lowest voltage and the worst capacity in
the battery pack as the object of the capacity test;
b. Turn on the rectifier to charge the battery pack, and wait for the
battery pack to be stable for more than 1 hour after it is fully charged;
c. Conduct a 10-hour rate discharge test on the worst battery found during
discharge in a. Measure the terminal voltage, temperature, discharge time and
room temperature of the battery before and after discharge. In the future, the
test will be performed every 1 hour. When the discharge is approaching the
termination voltage, the test should be performed at any time in order to
accurately record the discharge time:
d. The discharge time multiplied by the discharge current is the capacity
of the battery. When the room temperature is not 25°C, it should be converted
into the capacity at 25°C according to formula (1);
e. After the discharge test, use a charger to charge the battery to restore
its capacity;
f. Draw the discharge curve based on the measured data;
Method 3: Verification capacity test method
In order to know the approximate capacity of the battery pack at any time,
it is necessary to conduct a verification discharge test. The method is:
a. In the DC power supply system, turn off the switching power supply and
let the battery power the communication equipment. Test the terminal voltage,
temperature, specific gravity, room temperature and discharge time of each
battery before and after the battery pack is discharged, and discharge 30%-40%
of the rated capacity. until;
b. After discharging, recharge the battery;
c. Make a discharge curve based on the test data and keep it for comparison
when testing again;
Precautions:
The above three battery capacity test methods are commonly used in daily
maintenance, but no matter which method is used, communication security will be
threatened to a certain extent during the capacity test. Therefore, when doing
the capacity test, it is necessary to prevent the mains power from being
interrupted, and the backup power generation unit should be in good
condition.
5), periodic maintenance projects
monthly maintenance
Complete the following inspections monthly:
1. Keep the battery room clean and hygienic;
2. Measure and record the ambient temperature in the battery room;
3. Check the cleanliness of the batteries one by one, the damage and
heating marks of the terminals, and the damage or overheating marks of the
casing and cover:
4. Measure and record the total voltage and float current of the battery
system;
Quarterly maintenance
1. Repeat various monthly inspections;
2. Measure and record the float voltage of each online battery. If the
voltage of more than two batteries is lower than 2.18V after temperature
correction, please contact the manufacturer.
Annual maintenance
1. Repeat all quarterly maintenance and inspections;
2. Check the connection parts every year for looseness;
3. Every year, the battery pack undergoes a verification discharge test
with actual load, and discharges 30%-40% of the rated capacity;
Three years maintenance
A capacity test is conducted every three years, and once a year after six
years of use. If the actual discharge capacity of the battery pack is less than
80% of the rated capacity, the battery pack is considered to have expired.
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