VRLA Battery: Working Principle, Capacity and Maintenance

Catalog

I. Working Principle of VRLA battery

Because VRLA batteries are fully sealed, will not leak acid, and will not emit acid mist when charging and discharging like old lead-acid batteries, which will corrode equipment and pollute the environment, VRLA batteries are also called 'Airtight (sealed) lead-acid batteries' based on its structural characteristics. In order to distinguish, the old lead-acid batteries are called open-ended lead-acid batteries. As the VRLA battery is not only fully sealed from the structural point of view, but also has a valve that can control the gas pressure inside the battery, so the full name of the VRLA lead-acid battery becomes "valve-regulated sealed lead-acid battery".

As we all know, the VRLA battery is also a lead-acid battery, it should have the same working principle as an open-type lead-acid battery. This means that the carrier for energy conversion and energy storage of VBLA batteries is the same as the open type, and the substances participating in the electrochemical reaction are also the same. When charging, the positive electrode is converted from lead sulfate (PbSO4) to lead dioxide. (Pb02) converts electrical energy into chemical energy and stores it in the positive plate; the negative electrode is converted from lead sulfate (PbSO4) to spongy lead (spongy Pb) and then converts electrical energy into chemical energy and stores it in the negative plate. During discharge, the positive electrode changes from lead dioxide (PbO2) to lead sulfate (PbSO4) to convert chemical energy into electrical energy to supply power to the load, and the negative electrode changes from spongy lead (spongy Pb) to lead sulfate (PbSO4) to change the chemical Can be converted into electrical energy to supply power to the load.

In addition, the amount of material (the amount of active material) that can participate in energy conversion in the positive plate and the amount of material (the amount of active material) that can participate in energy conversion in the negative plate must match each other. If there is no match, if one is more and one is less, the extra part is a waste, and the amount of each substance that participates in the electrochemical reaction matches with another substance is different.

The electrochemical equivalent of each active material is calculated from its electrochemical reaction equation. The whole content (including electrochemical equivalent) of the working principle of the lead-acid battery mentioned above can be expressed by the following electrochemical reaction equation:

PbO2+Pb+2H2S04←→2PBS04+2H20

When the above electrochemical reaction formula proceeds from left to right, it is the discharge reaction of the battery. When the above electrochemical reaction formula proceeds from right to left, it is the charging reaction of the battery.

II. Capacity of VRLA battery

1. Capacity and Temperature

When the battery discharge working temperature is not the reference temperature of 25℃, the actual capacity should be converted to the capacity at 25℃ according to the following formula. That is when the test environment temperature is not 25℃, the capacity needs to be corrected.

Ce=Ct/[1＋KT(T－25℃)](2)

In the formula: Ct is the measured capacity, Ce is the actual capacity at 25℃ (as the nominal capacity), KT is the temperature coefficient, and T is the actual temperature.

For 10h rate discharge, KT=0.006/℃; 3h rate discharge, KT=0.008/℃, 1h rate discharge, KT=0.01/℃.

2. Capacity and Plate Weight

The lead plates used in VRLA batteries are similar to the basic materials of car batteries, and the weight and appearance are slightly different. For example, the 12V/100Ah VRLA battery and the car battery plates made by the same manufacturer are only different in appearance and weight, and the latter is slightly smaller. This is because the car battery plate is slightly thin, but the nominal capacity is the same.

3. Capacity and Service Life

VRLA batteries of the same capacity can have different design life, which mainly depends on the manufacture of the plate, weight, and valve sealing method, even if the battery of the same manufacturer has different valve sealing methods, the plate manufacturing size may be different. The difference in the design life of 6 years, 10 years, and 20 years. In general, the weight of the plates of a 20-year battery should be about twice that of a 10-year battery. This can also be explained by Faraday's law of electrochemistry. The weight of a 200Ah battery should be about twice that of a 100Ah battery. VRLA batteries of the same capacity from various manufacturers have similar weights.

In addition, the actual service life is very different from the design service life, which mainly depends on the loss of water in the VRLA battery. The design life can be reached under the design conditions, and when the external conditions such as temperature, voltage, depth of discharge, and other changes exceed the design requirements, the actual service life will be much lower than the design life, and the capacity will also change, which tends to decrease.

III. Monitoring and Maintenance of VRLA battery

1. Monitoring of VRLA battery

VRLA battery is difficult to monitor battery capacity and performance due to its sealed and liquid-absorbing structure. Compared with traditional open-type batteries, it cannot see the liquid level and the plate, nor can it smell sour, nor can it measure the specific gravity and Internal pressure, etc., and battery failure or battery capacity reduction is mainly caused by dehydration and plate vulcanization. Only external measurement of VRLA battery open-circuit voltage cannot be used to determine the battery capacity [a battery that drops to 80% of the nominal capacity is determined It is a sufficient basis for failure].

There are currently several capacity monitoring methods as follows:

(1) Online conductivity test

In the United States, Germany, Britain, and other countries, VRLA batteries generally use conductivity technology to detect their capacity. This method does not require discharge or inspection of the VRLA battery. For example, the patented conductivity meter of Midtronics in the United States belongs to the online measurement method.

The principle is to add a low-frequency AC measurement signal voltage to both ends of a group of VRLA batteries. The ratio of the signal current through the battery to the signal voltage is the conductance (only the real part of the admittance is considered) and the unit is mho (or Siemens), Which reflects the current conduction capability of the battery when it is online at this time. For this reason, conductance value measurement curve files should be established during installation, so that during periodic testing, if the conductance value is found to be lower than 80% of the initial measured value at this time, the battery capacity is already lower than 80% of the nominal capacity. The specific operation method can be seen as a relevant Product Manual.

(2) Dummy load discharge

Like measuring the capacity of a traditional open battery, a false load discharge test is still a more practical way.

When there are two sets of backup batteries, you can choose one set to exit the system, and then use a dummy load to perform a discharge test on it. This can actually detect the capacity of the VRLA battery 100%. It is necessary to pay attention to the discharge of a certain battery specified by some manufacturers. The termination voltage is 1.75V/cell, while some manufacturers specify 1.80V/cell.

Generally, at the beginning of the discharge, there is a steep drop from the terminal potential to the closed-circuit voltage (for example, from 2.20V to about 2.05V, and then a straight line between 2.0~1.8V voltage, and after the discharge to the termination voltage, the battery The terminal voltage will drop sharply towards 0V, showing a steep drop diving curve).

According to the national standard, the battery is discharged at a rate of 10 hours, and the C10 nominal capacity value Ce is measured, and the discharge current is 0.1IC10A. If discharging at a rate of 3 hours, the discharge current should be 0.25IC10A, that is, the capacity is 75% Ce; if discharging at a rate of 1 hour, the discharge current should be 0.55IC10A, that is, the capacity is 55% Ce.

(3) Visual inspection method

Check the appearance for swelling and depression of the battery shell, discoloration of the connecting strip, discoloration of the cable head and connecting screw, etc., whether there is acid mist or other peculiar smell, the touch cable is overheated, the shell is overheated, etc.

In addition, a voltmeter can also be used to check whether the voltage between groups is consistent, whether the voltage of each battery in the group is consistent (generally the battery capacity decreases because of the increase in internal resistance, and the battery voltage with large internal resistance is also higher), and the battery Whether the voltage is lower than 12V (if the rechargeable battery is disconnected from the floating charge source, there are still individual batteries whose voltage is lower than 12V, it may be damaged).

You can also open the valve cover (generally prohibited to open, but if you have serious doubts about the battery, you can quickly open the valve cover and close it again, pay attention to tightening when closing), check whether the electrode plate is vulcanized and whether the inside of the absorbent glass fiber has dried up, etc.

2. Maintenance of VRLA battery

In actual operation, VRLA batteries have relatively high requirements for ambient temperature, and the best ambient operating temperature for VRLA batteries is 20-25℃. If the use environment temperature is too high, the heat generated during charging of the VRLA battery cannot be diffused into the air in time, which accelerates the loss of electrolyte, and at the same time, it is easy to lose water through the shell, which will increase the specific gravity of the electrolyte. The corrosion of the positive grid eventually leads to the premature failure of the VRLA battery because it does not reach the battery design life.

In order to avoid premature failure of VRLA batteries, strict maintenance should be carried out on VRLA batteries, and the switching power supply should be set strictly according to the relevant setting parameters provided by the manufacturer. Normally, the float charging voltage should be adjusted in time according to the operating conditions of the battery and charging equipment, so that the float charging voltage meets the requirements of the VRLA battery, avoiding excessive voltage and causing the loss of water caused by the overcharging of the battery; at the same time, preventing the voltage from being too low. The undercharge of the VRLA battery causes the sulfation of the battery plates, which greatly reduces the capacity of the battery. The advanced operating equipment has a temperature compensation function and can automatically adjust operating parameters according to the operating environment.

In order to understand the status of the VRLA battery in time, the capacity of the VRLA battery is checked regularly to accurately grasp the actual status of the VRLA battery capacity, so that corresponding maintenance measures can be taken in time. Regularly maintain the battery so that the VRLA battery is always in good operating condition. For VRLA batteries, only when a strict operation is carried out according to the manufacturer's requirements, will the life of VRLA batteries be truly close to their design life, otherwise, the life of the battery will be shorter than that of ordinary batteries.