The risk of insufficient petroleum resources has forced human beings to emphasize the acquisition and storage of energy. To avoid such situation, this study tends to explore the effective management of lead-acid batteries for effective utilization conforming to the industrial requirements.
The advance of information technology has enhanced people’s requirements for the quality of life. Nevertheless, the risk of insufficient petroleum resources has forced human beings to emphasize the acquisition and storage of energy. In 2006, two types of batteries appeared in the US top ten technology plan, in which lead-acid batteries covered one-third of the gross sales in the battery industry. In addition to the close relations with power, traffic, and information, lead-acid batteries presented the control power in the transportation, like vehicles and various uninterruptible power systems so as to become a necessary product in human life. Lead-acid batteries [
The boom of green industry makes resource reengineering and energy conservation the key issues for enterprises to invest in a lot of resources to protect the environment. For instance, green economy or green industry has been regarded as the key development in China’s 12th Five-Year Plan. Apparently, green industry is not only an emerging industry but also a trend. Particularly, the global focus on energy protection in the past years has promoted the concepts of energy conservation and carbon reduction. Besides, the shortage of oil production, natural gas, and coal makes the resource application extraordinarily important. A lot of researchers therefore constantly study energy conservation, aiming to effectively utilize the present resources on the earth for the extreme benefits. This study aims to achieve the energy conservation and environmental protection through the effective management of lead-acid batteries.
According to the reports in Mainland China, lead-acid battery producers are requested to recycle the products, meeting the requirements of the industrial management in Mainland China for it is the embodiment of social responsibility as well as the key in the sustainable development of green economy. For enterprises, secondary lead, as the cold iron in reducing costs and enhancing efficiency, has played a critical role in the increasing production of lead-acid batteries [
The lead-acid battery industry is the key in the development of secondary energy that battery enterprises have stressed on the applications to consumer products. Lead-acid batteries, which are mainly applied to the energy storage of vehicles, uninterruptible power supply (UPS), electric cars, medical equipment, and communication devices, have been used for a century land provided that the market structure is mature and stable. In order to maintain the normal operation of precision instruments in high-tech plants and medical industry, uninterruptible power supply is often utilized for keeping the power supply stable. Nevertheless, uninterruptible power supply requires a large amount of lead-acid batteries [
Lead-acid batteries are widely applied and play a primary role in human demands, such as the equipment of information, telecommunication, traffic, industry, and medical systems. Lead-acid batteries are mainly applied to high-tech plants and medical industry, particularly to uninterruptible power supply, which has to be discarded every few years as it is used as a spare. The chemical pollution of lead and sulfuric acid in the process of dealing with used batteries could seriously impact the environment. Hence, the effective management of lead-acid batteries is considered as a critical issue [
The dynamic characteristics of lead-acid batteries are complicated and would change with battery ageing. However, the research on the management of lead-acid battery testing tends to explore the effectiveness of lead-acid batteries for the users to understand the power supply, the capacity, and the discard time to ensure the system stability and the maximal effectiveness. The maintenance cost could be reduced by verifying the health of each battery and providing managerial strategies to ensure the discard time of batteries, and the maintenance strategy is adjusted from advancing the currently time-based regular discard to condition-based according to the real discharge testing. Instantaneous current discharge, a highly reliable online testing with low destruction, is introduced and can actually record DC resistance, float voltage, discharge voltage, and recovery voltage in the discharge process for analyzing the single battery capacity and capability. Moreover, it allows online testing and the reliability of uninterruptible power supply in plants to be maintained. Such an approach is expected to accurately estimate the state of availability to find out the degraded batteries for early discard and ensure the system reliability. This study aims to find out degraded batteries for early discard and ensure the reliability of uninterruptible power supply, verify the health of each battery to ensure the actual discard time and reduce the maintenance costs, test online without affecting the normal operation of systems.
This paper is expected to achieve the objectives of predictive maintenance and effective utilization of batteries, energy conservation, cost reduction, and environmental protection. The managerial experiences and approaches of lead-acid battery suppliers and technology plants are considered as the reference of this study. By analyzing and recording the data, the research results are inferred from the effective data, which could be the reference of enterprises and the academia. The enterprises therefore could decrease the waste of lead-acid battery discard and reduce the discard cost. What is more, the heavy metal pollution caused by lead-acid battery discard could be reduced through the effective management of lead-acid batteries so as to protect the environments and contribute to the earth.
The battery state could be divided into state of charge and state of health, in which several correlations and parameters that could affect the battery performance [
Battery state flow.
Lead-acid batteries present the characteristics of battery capacity and voltage, discharge characteristics, and preservation of lead-acid batteries [
Regarding the irreversible life of lead-acid batteries, a battery is considered terminated when the dischargeable capacity is lower than 80% of rated capacity, according to IEEE Std 1188. In accordance with the discharge capability, the service life of lead-acid batteries could be divided into stable phase, with more than 100% discharge capability, decline phase, with 100%~80% discharge capability, breakdown phase, with 80%~35% discharge capability.
When the discharge capability is lower than 80%, the internal polar plate would rapidly degrade and enter breakdown phase, when the battery should be discarded, according to IEEE Std 1188. Nevertheless, a battery can still serve for a long period of time after the time point. In consideration of the operation costs, lowering the discharge capability standard for battery discard could reduce the cost and increase the profit. However, the internal polar plate enters breakdown phase with rapid degradation that the quality of power supply for equipment might be affected and even cause operation risks and loss when the discard time is delayed. Therefore, it is a major issue for battery managers making the optimal discard time.
The judgment of battery life is generally defined according to the usage, including cycle life and float life.
Depth of discharge: overdischarge could shorten cycle life. Large-current discharge: discharge with small capacity and then large current could shorten the service life. Large-current charge: the gas generated by extreme charge current could exceed the absorption rate of batteries at a certain amount to increase the internal pressure causing the gas being exhausted from the security valve. The electrolyte therefore would be largely consumed to damage the components in the battery. Overcharge: the components in a battery would be damaged by the electrolyte resulting from overcharge. Effects of environmental temperature: high temperature would accelerate the degradation of components in a battery. The battery life would be shortened when charging with fixed voltage but unnecessary large current in high temperature. Hydrogen generated in extreme low-temperature charge could increase the internal pressure or decrease the electrolyte to shorten the service life.
Current technologies for measuring the lead-acid battery state contain open circuit voltage, electrolyte specific gravity, internal resistance, charge ripple current monitoring, and offline load control [
In accordance with the experimental requirements in this study, instantaneous current discharge is chosen for measuring lead-acid batteries for it could easily control the current state of batteries and exclude unnecessary resistance errors. Hence, the testing data are more precise for analyzing the state and the discharge capability of lead-acid batteries. In order to achieve the effective management of lead-acid batteries, the successive management is further evaluated according to the analyzed data.
Based on the research variables of batteries, current, voltage, and battery state, the unit and codes are defined as follows: Battery Code (NO.). Service Time (Time; Unit: Month). Float Voltage (FV; Unit: V). Discharge Voltage (DV; Unit: V). Discharge Current (DA; Unit: A). Internal Resistance ( Battery State (Check; 1: OK, 2: WARNING, 3: EXCEPTION).
The following hypotheses are proposed for the batteries so as to exclude some special situations and make the research results more precise. The longer service time (Time), the lower discharge voltage (DV). The longer service time (Time), the higher internal resistance ( Battery state (Check) is correlated with service time (Time), discharge voltage (DV), and internal resistance (
To effectively test the state and discharge capability of lead-acid batteries in uninterruptible power supply in technology plants, instantaneous current discharge is selected as the measurement in this study by testing the battery state with a measuring device and analyzing the tested discharge data with software.
According to the process, more than two people are required to securely and accurately complete the research. The measuring devices are checked in the beginning of the research to ensure the usability. The condition of uninterruptible power supply is further confirmed to exclude the exception. The operation and evacuation routes are also confirmed for the operators’ security. Furthermore, the measuring device parameters are set for starting the experiment. In the testing process, each cell checked the discharge characteristics every 0.5 sec, and the characteristics of recovery voltage are also measured every 0.5 sec for testing the terminal voltage change. In addition, the voltage monitoring terminal is connected to the terminal of energy storage pool and the discharge current probe is directly linked to the battery terminal for diagnoses. The device is also checked for the misconnection. When there is exception resulting from misconnection, the device would alert the operator to ensure the operation security. Finally, the measured data are read for data analyses to explore the effective information for the effective management of the personnel in technology plants and cost reduction.
Instantaneous current discharge is selected as the measurement in this study, as it is suitable for measuring the state of lead-acid batteries in uninterruptible power supply in technology plants with the following advantages. Instantaneous current discharge could control the capacity state and the starting ability of a single battery. DC resistance measured from the real discharge could be used for analyzing the degradation of polar plates and the terminal break and false welding of power collector as well as avoiding AC resistance errors. The float voltage data are applied to understanding the balance analysis of charge voltage and the examination of short circuit batteries. The recovery voltage data allow analyzing the factors in the electrolytic degradation.
An instantaneous discharge device is utilized in this study for finding out the degraded batteries with the testing information and preceding the control according to the current time and state of lead-acid batteries to assist technology plants in achieving the effective management.
In accordance with instantaneous current discharge, the relationship between lead-acid battery voltage and time is applied to collecting the testing data for the statistical analyses of service time, internal resistance, discharge voltage, and float voltage, which are compared with basic statistical analysis, regression analysis, and discriminated analysis for the effective management.
Based on the above research process, this study practiced measuring device checking, uninterruptible power supply checking, researcher security, measuring equipment parameter setting, float voltage testing, and discharge testing for effectively testing the battery state and understanding the real change time of batteries to reduce the costs.
The batteries in uninterruptible power supply in technology plants are discussed in this study. Total 16 batteries are recorded in the actual measurement, and total 64 pieces of data are acquired by recording Battery code (NO.), service time (Time; Unit: month), float voltage (FV; Unit: V), discharge voltage (DV; Unit: V), discharge current (DA; Unit: A), internal resistance (
Float charge voltage of the lead-acid batteries.
The experimental results show that discharge voltage of lead-acid batteries tends to be stable with the value in 12.7–12.2. However, comparing the batteries which are placed for 102 months with the control lead-acid batteries, discharge voltage gradually decreases. From the line graph of discharge voltage (Figure
Discharge voltage of lead-acid batteries.
In accordance with the statistical data of batteries at 8, 49, 89, and 102 months, the internal resistance at the 8th month is smaller, while the relative large value is revealed at the 102nd month when problems are likely to appear. From Figure
Internal resistance of lead-acid batteries.
By observing the testing data, 16 batteries in 8 months are OK, showing the low probability of EXCEPTION; 15 batteries in 89 months are OK; merely one presents WARNING, showing that the batteries start degrading but are still secure. The battery state change therefore should be concerned for the management. Three batteries in 102 months show WARNING, and the rest 12 batteries reveal EXCEPTION, presenting the serious battery degradation that batteries after 102 months can no longer be used. In this case, the managers should make decisions on the battery discard.
Table
Basic statistics.
Variable | Time | FV | DV | DA |
|
Check |
---|---|---|---|---|---|---|
Mean | 62 | 13.431 | 12.224 | 98.656 | 12.605 | 1.438 |
Median | 69 | 13.393 | 12.533 | 100 | 4.697 | 1 |
Maximum | 102 | 13.624 | 12.695 | 100 | 461.551 | 3 |
Minimum | 8 | 13.292 | 0.666 | 14 | 3.906 | 1 |
Standard deviation | 37.081 | 0.097 | 1.496 | 10.750 | 57.032 | 0.794 |
The regression analysis of the samples involve service time (Time) and discharge voltage (DV); according to the analysis, the model correlation coefficient is low as shown as Table
Service time and discharge voltage of regression analysis.
Variable | Coefficient estimates | Standard deviation |
|
|
Significant |
|
---|---|---|---|---|---|---|
Constant | 12.937 | 0.354 | 36.54 | <0.0001 | 1% | 0.0665 |
Time | −0.0115 | 0.0049 | −2.34 | 0.0224 | 5% |
After excluding the outlier, the test on service time (Time) and discharge voltage (DV) keeps do regression analysis; according to it, the model correlation coefficient increases up to 0.6072. Apparently, discharge voltage of lead-acid batteries would be affected by service time that the negative correlation appears under the significance 5%. It shows that the longer service time would reduce discharge voltage (Table
Regression analysis (excluding outliers).
Variable | Coefficient estimates | Standard deviation |
|
|
Significant |
|
---|---|---|---|---|---|---|
Constant | 12.787 | 0.0450 | 283.93 | <0.0001 | 1% | 0.6072 |
Time | −0.0062 | 0.0006 | −9.84 | <0.0001 | 5% |
The regression analysis on service time (Time) and internal resistance (
Service time and internal resistance of regression analysis.
Variable | Coefficient estimates | Standard deviation |
|
|
Significant |
|
---|---|---|---|---|---|---|
Constant | 3.2847 | 0.2354 | 13.96 | <0.0001 | 1% | 0.6538 |
Time | 0.0358 | 0.0033 | 10.87 | <0.0001 | 1% |
Regression analysis is preceded for battery state (Check) towards internal resistance (
Battery state, internal resistance, and discharge voltage.
Variable | Coefficient estimates | Standard deviation |
|
|
Significant |
|
---|---|---|---|---|---|---|
Constant | 86.9502 | 14.9149 | 5.83 | <0.0001 | 1% | 0.7507 |
DV | −6.5462 | 1.1146 | −5.87 | <0.0001 | 1% | |
|
−0.7881 | 0.2002 | −3.94 | 0.0002 | 1% |
Finally, the measurement of discriminant analysis has to be done. The normal (OK) samples present 75%, the ones with WARNING show 6.25%, and the defective ones (NG) reveal 18.75%, where misjudging OK as NG appears once, 2.08%. In summary, the normal judgment (OK) appears to be 97.92%, the ones of WARNING present 100%, and the defective ones (NG) are 100%. The overall misjudgment proportion presents the accuracy of the verification. Table
Battery state of discriminant analysis.
Check | OK | Warning | NG | Total |
---|---|---|---|---|
OK | 47 | 0 | 1 | 48 |
97.92% | 0% | 2.080% | 100% | |
|
||||
Warning | 0 | 4 | 0 | 4 |
0% | 100% | 0% | 100% | |
|
||||
NG | 0 | 0 | 12 | 12 |
0% | 0% | 100% | 100% |
The experimental results of lead-acid batteries show the positive proportion between the battery degradation and time. The change appears on the end of battery life when it accelerates the degradation. Figure
Discharge voltage/internal resistance distribution.
It is suggested in IEEE Std 1188 that lead-acid batteries with the discharge capability lower than 80% should be discarded. Nevertheless, batteries can still be used for a period of time after the time point (as the measured discharge voltage in Figure
Based on the internal standard process, the lead-acid batteries in uninterruptible power supply should be discarded after 4 years (48 months). When the data showed WARNING, service time might be prolonged to 7 years. In the case company, total 9,559 lead-acid batteries were purchased in different years. According to the standard process, about 136.8 million NT dollars are required for battery discard in 2004–2020. When the discard time is prolonged to 7 years (84 months), total 88.215 million NT dollars is required for battery discard in 2004–2020. Total 48.595 million NT dollars therefore could be reduced in the 16 years that about 3 million NT dollars is reduced annually.
The analysis results show that the approach could accurately judge the battery state. Except bad quality or end of battery life, internal resistance and discharge voltage degrade slowly and continuously, which might be measured after several months. Based on the concept, the battery maintenance is classified into new, midterm, and end-term for tests. New batteries are the ones newly purchased, which could be defined as feedstock tests when the batteries are tested in the beginning of purchase so as to reduce the risk of bad quality. Moreover, there are several factors in the residual capacity and service life of lead-acid batteries, including battery structure, environmental temperature, depth of previous discharge, self-discharge, discharge current, charge method, and end of discharge voltage. The end-term batteries are therefore defined as service time over a half of the battery life. The test is then shortened from 6 months to 3 months, expecting to find out the breakdown, proceeding with maintenance and discard, and ensure the system reliability, other than those defined as midterm batteries, which are relatively stable and show lower risks of breakdown. The test proceeds once a year to reduce the work load of the testing personnel.
Aiming at the management of degrading lead-acid batteries in uninterruptible power supply in technology plants, a testing method not affecting the online testing is selected. A battery testing process is established according to the research results, expecting to change the time-based regular testing into active condition-based maintenance, which detects the device parameters and adopts proper maintenance before the exception or breakdown. Such a testing strategy presents the following features. In consideration of time, accuracy, and online detectability, the discharge is checked in short time, and DC resistance, float voltage, discharge voltage, and charge voltage are recorded in the process to provide a testing method for battery state. The battery management is provided for technology plants, expecting to verify the health of each battery, find out the degraded batteries for discard, and confirm the actual discard time of batteries. Hence, it is able to ensure the system reliability and provide users with managerial strategies. Aiming at reducing the maintenance cost, current time-based regular testing for advance discard is adjusted to condition-based maintenance based on the discharge tests.
Under the fierce competition in modern technology industry, cost reduction is always the requirement of managers. Nevertheless, in consideration of device operation maintenance and system stability, the optimal device maintenance strategy could minimize the maintenance cost and maximize the system stability.
In the regular testing process, setting the measuring cycle might be difficult. A long cycle might reduce the number of testing times but increase the risk of exceptional batteries not being checked. A short cycle could cause overmaintenance and manpower load because of the increasing number of testing times and testing manpower costs. Factors in battery life are numerous that instantaneous current discharge is applied to establishing a management method in this study. It could not only ensure the system stability in the plant but also acquire the maximal use effectiveness, reduce the maintenance cost, enhance the company competitiveness, and reduce the impact of used batteries on the environment by decreasing unnecessary battery discard so as to contribute to the environmental protection and waste reduction.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported partially by the introduction of talents Huaqiao University Scientific Research Projects (Project no. 13BS412).