Lead-acid battery fault analysis
In the detection process of the lead battery, the lead battery will often encounter a fault and abnormal data, so that the detection cannot be conducted or the test is terminated early. Therefore, it is very important to master the fault analysis for the detection work。
1. Failure phenomenon and cause
1.1 The phenomenon and causes of the reverse pole
The reverse pole of lead battery refers to the change of the positive and negative poles of the battery. The reverse pole phenomenon is reflected in two aspects. One is that a single cell battery plate group is reversed or the whole battery plate group is reversed when lead battery is assembled. In this case, the terminal voltage value is less than the sum of the rated voltage of each single battery or the terminal voltage is negative when the voltmeter is used to measure the terminal voltage of the lead battery after the acid is filled. On the other hand, lead battery in capacity discharge in multiple series use, due to a battery (or a single battery) capacity is low or completely lost capacity. In the discharge process, the battery is quickly discharged and reverse charged by other batteries, so that the original negative electrode into positive, the original positive electrode into negative, terminal voltage appears negative value phenomenon.
For the first reverse pole fault, when measuring the battery terminal voltage it can be found, if there is a single cell reverse pole, not only lose the 2V voltage of the battery, but also increase the 2V reverse voltage, the end voltage to reduce about 4V. For example, if the rated voltage of a battery is 12V and the terminal voltage is about 8V, there is one single-cell battery reverse pole. If the measured terminal voltage is about 4V, it indicates that there are two single-cell mirrors; if the measured terminal voltage is about -4V, it indicates that there are four single-cell mirrors; if the measured terminal voltage is -12V, it indicates that there are six single-cell mirrors.
For the second fault, the terminal voltage (negative value) varies with the discharge condition. Generally, when detecting, the battery should be removed from the discharge line in time for this situation, so as not to damage the battery.
1.2 Short-circuit phenomenon and causes
1.2.1 The short circuit of the lead battery refers to the connection of the positive and negative plate groups inside the lead battery. The short circuit phenomenon of lead battery is mainly manifested in the following aspects:
a.The open circuit voltage is low, and the closed circuit voltage (discharge) quickly reaches the termination voltage
b.During the high rate discharges, the end voltage quickly drops to zero.
c.In the open circuit, the electrolyte density is very low, and the electrolyte will freeze over in low temperatures.
d.During charging, the voltage rises slowly and always remains low (sometimes down to zero).
e.During charging, the electrolyte temperature rises very high and very quickly.
f.During charging, the electrolyte density rises slowly or almost unchanged.
g.During charging,no bubbling or bubbling appears very late.
1.2.2 The main reasons for the internal short circuit of lead batteries are as follows:
a.The quality of the separator is not good or defective, so that the plate active material passes through, resulting in virtual or direct contact between positive and negative plates.
b.The separator misalignment causes the positive and negative plates to connect.
c.The active material on the plate expands and falls off. Due to excessive deposition of the active material, the lower edge or side edge of the positive and negative plate is in contact with the sediment, resulting in the connection of the positive and negative plate.
d.Conducting objects fall into the battery, causing a positive and negative plate connection.
e. The ‘lead flow’ formed during the welding of the plate group is not completely removed, or the ‘lead bean’ exists between the positive and negative plates during assembly. During the charging and discharging process, the separator is damaged and the positive and negative plates are connected.
1.3 Phenomena and causes of plate acidification
1.3.1 Plate acidification refers to the formation of white hard lead sulfate crystals on the plate, but it is very difficult to convert to the active substance when charged. There are mainly the following phenomena after lead-acid battery plate acidification:
a.The voltage of lead battery rises rapidly in the charging process, and its initial and final voltage is too high, and the final charging voltage can reach about 2.90V / single cell.
b.In the discharge process, the voltage drops quickly, that is, prematurely to the termination voltage, so its capacity is significantly lower than that of other batteries.
c.When charging, the electrolyte temperature rises quickly and easily exceeds 45℃.
d.During charging, the electrolyte density is lower than the normal value, and bubbles occur prematurely during charging.
e.The color and condition of the plate were abnormal when the battery was dissected. The positive plate is light brown (normal is dark brown), the plate surface has white lead sulfate spots, the negative plate is offwhite (normal is gray), the plate surface is rough, touch as if there is a feeling of sand, and the plate is hard.
f.Severe sulfation, The white crystal of lead sulfate formed by the plate is coarse and cannot be recovered into active substance under normal circumstances.
1.3.2 Plate acidification is mainly caused by the following reasons.
a.Lead battery initial charging is insufficient or the initial charging interruption time is long.
b.Long-term insufficient charging of lead battery.
c.Failure to charge in time after discharge
d.Frequent excessive discharge or low current deep discharge
e.If the electrolyte density is too high or the temperature is too high, the lead sulfate will form deeply and is not easy to recover.
f.Lead battery is shelved for a long time, and it is not used for a long time and has not been regularly charged.
g.Internal short circuit local action,or there’s much water on the battery surface causing electric leakage.
h.The electrolyte is not pure, and the self-discharge is large.
j.The low electrolyte level inside the battery makes the exposed part of the plate acidified.
Under normal use of lead batteries, the active substances (Pb02 and Pb) on the positive and negative plates are mostly transformed into small crystalline lead sulfate. These soft and small crystalline lead sulfate are evenly distributed on the porous active substances, and can easily contact with the electrolyte during charging and recover to the original substances PbO2 and Pb.
If in use due to the above improper use of various reasons, the active substance on the plate will gradually form lead sulfate with coarse crystalline grains, these coarse and hard lead sulfate crystals have large volume and poor conductivity, which will block the fine pores of the active substance on the plate, hinder the penetration and diffusion of the electrolyte, and increase the internal resistance of the battery. At the same time, when charging, The coarse and hard lead sulfate is not as easy to convert into PbO2 and Pb as the soft and small grain lead sulfate. If the duration is too long, the coarse and hard lead sulfate will lose its reversible effect, resulting in the effective material reduction of the plate discharge capacity, service life is shortened.
When the battery produces irreversible sulphate, it should be repaired according to the severity of its degree. If the acidification is light, the general activation charging (that is, balanced charging) can be restored to normal. The specific methods are as follows: Constant voltage and current limiting charging: the first stage 0.18C 2A charging to 2.7V/ single cell charging 12-24 hours. The first stage of constant current: 0.18C 2A charging to 2.4V/ single cell; the second stage: 0.05C 2A charging for 5-12 hours. For those with more severe acidification, it needs to be activated to return to normal.
1.4 Plate bending and corrosion fracture
1.4.1 Plate bending mostly occurs in the positive plate, and the negative plate rarely occurs, some negative plate bending is because the positive plate is bent too much and even forced the negative plate to bend accordingly.
Plate fracture occurs frequently in the process of service life. Due to grid corrosion and strength become smaller, plate fracture is caused, especially the positive grid performance is more serious. The main reasons for plate bending are as follows:
a. The active substance of the plate is not uniform in the formation or paste distribution in the manufacturing process, therefore, in the charge and discharge, The electrochemical of each part of the plate is not uniform, resulting in the expansion and contraction of the volume of the active material on the plate is inconsistent and cause bending, and some cause cracking.
b.Excessive charging or excessive discharge increases the expansion and contraction of the inner layer of active material, and the recovery process is inconsistent, resulting in the bending of the plate.
c.When high current discharge or high temperature discharge, the active material reaction of the plate is more intense, easy to cause uneven chemical reaction and cause the plate bending.
d.Battery contains impurities, in causing local action, only a small part of the active substance transferred into lead sulfate, resulting in the volume of the active material plate is not consistent, resulting in bending.
1.4.2 Positive plate corrosion and fracture is mainly caused by the following reasons:
a.There is a problem in the manufacturing process of plate grid alloy, which causes the plate to break due to poor corrosion resistance in the process of charging and discharging.
b.When charging, the positive grid is under the condition of anode polarization, and frequent overcharging is the main reason for the corrosion and fracture of positive plate.
c.The electrolyte density is too high, the temperature is too high, and the positive plate oxidation corrosion is intensified.
d.Lead battery electrolyte, containing positive grid corrosive acid or other organic salts, will gradually corrode the positive grid. These acids and salts that are harmful to the positive grid may come from sulfuric acid distilled water, or may leach from the separator or other components, so that the plate or the positive grid is constantly corroded during the charge-discharge cycle.
e.The process of positive plate corrosion, which is the process of oxide film generation, so the linear size of the grid increases, which causes the deformation or expansion of the grid.
1.4.3 Characteristics of corrosion and deformation of the positive grid:
a.The electrolyte was cloudy and the plate was decayed.
b.The active substance of the positive plate, due to the corrosion of the grid, loses its due strength and solidification, resulting in shedding, which is often in the form of block granular.
c.Due to the corrosion of the positive grid, the active substance falls off, which not only destroys the fine pore structure of the active substance, but also gradually reduces the amount of the effective substance. This will inevitably lead to the reduction of battery capacity and shortened cycle life.
1.4.4 Corrosion mechanism of positive grid:
a. Lead dioxide surface oxygen corrosion: when the anode is charged, the positive electrode oxygen precipitation, the oxygen in the form of "superchemical equivalent atoms" enter into the lead dioxide lattice, and diffused through the oxide layer to the metal surface, lead to the metal oxidation. The oxidation of metal is the basic process that determines the corrosion rate of the positive electrode of lead. The increase of temperature increases the polarization, resulting in the increase of oxygen diffusion rate and the acceleration of corrosion rate.
b.Catalytic corrosion: Lead dioxide acts as a catalyst in the reaction of oxygen precipitation from the positive electrode. When oxygen is precipitated, it appears as an intermediate free radical. For example: OH, O, H2SO4, etc., these intermediate products compound on the surface of lead dioxide, causing the lead dioxide film loose, so that the metal under the film dissolved, causing corrosion.
c.Lead ----- Solid phase corrosion of lead dioxide: there is a contact potential difference between lead and the active substance lead dioxide in the grid alloy. This potential difference is the cause of electron migration from lead to lead dioxide, so corrosion occurs.
d.There are two kinds of crystals in the lead dioxide, that is, α-PB02 and β-Pb02, the layer of direct contact with the grid is mostly α-PB02, the outer layer of Pb02 is mostly β-PB02, and the basic product of anodic corrosion is α-PB02.
e.The corrosion of positive plate during anode polarization is basically along the grain boundary. Because there is another outer layer of solid solution on the outer layer of each small grain of the alloy, the intergranular interlayer with different composition and grain itself is formed between the grains. The corrosion of the alloy occurs in the intergranular interlayer.
1.5 Shedding of active substance
In the process of lead battery charging and discharging, the active substance of the plate gradually falls off due to damage. This phenomenon mainly occurs at the end of cyclic charging and discharging. The main feature is that there is sediment in the electrolyte, and the battery capacity decreases. The shedding of active substances is a normal phenomenon if the service life of the battery is near the end, but it also causes the shedding of active substances of the plate in the following situations.
a.Due to the improper proportion of additives in the negative plate,it will cause the active substance to expand and fall off in the process of charge and discharge.
b.Charge and discharge current is large or excessive charge and discharge, long-term excessive discharge.
c.The electrolyte temperature and density are too high when charging.
d.A short circuit occurs in the external circuit during discharge.
e.The electrolyte is not pure.
f.Plate acidification or grid corrosion fracture.
1.6 Capacity reduction
There are several reasons why lead batteries fail to reach their rated capacity when discharging or reduce their capacity during charge-discharge process:
a.Plate group local short circuit
b.There is false welding in the series welding part of the battery. Therefore, the initial capacity is ok. With the charge and discharge process, the oxide film produced at the false welding site can be conductive, but the effect is not good
c.Grid corrosion a plate fracture, the active material falls off.
d.Plate acidification
e.Capacity discharge current is large, the electrolyte density is low or the electrolyte level height is not enough.
f.Charging and discharge equipment and measuring instrument are too poor or faulty.
g.When discharging, the electrolyte temperature is too low.
1.7 Abnormal voltage
1.7.1 The abnormal voltage characteristics of lead battery in the process of charge and discharge are as follows:
a.The open circuit voltage is low or the voltage is low during charging and discharging.
b.The voltage drops quickly to the termination voltage and the higher voltage recovers quickly after the discharge stops.
c.The voltage rises very high when charging, and when stopping charging, the voltage drops too low and too fast.
d.The voltage is negative during the discharge.
e.The voltage increases and the voltage is low when charging.
1.7.2 Abnormal voltage phenomenon generally has the following reasons:
a.Internal short circuit, reverse pole.
b.Plate acidification.
c.Plate corrosion fracture, active material shedding.
d.The electrolyte density is low or high.
e.Measure instrument errors or failure.
f.Poor contact at the connection site.
g.Negative plate shrinkage passivation
h.Over-discharge
j.Lack of charge
l.High self discharge
1.8 Poor start performance
Poor starting performance of lead battery means that it fails to reach the required value during high current discharge. It is generally caused by the following reasons:
a.There occurs false welding between battery connection bar (wall welding) and end column and pole joint, plate strap and plate joint , resulting in poor starting performance or can not start.
b.Low electrolyte density, large internal resistance, large internal resistance of separator.
c.Positive plate bending and plate acidification.
d.The contact resistance between the discharge device and the battery is high
e.The plate group is short circuited. The plate is connected
f.The active material falls off
g.Product structure, process formula has problems.
h.Excessive discharge current.
j.The ambient temperature is too low.
1.9 Short cycle life
The reasons for the early termination of lead battery life are generally as follows:
a.Positive plate corrosion, negative plate expansion.
b.The plate group is short circuited. The plate is connected
c.Separator damage or misalignment and separator poor corrosion resistance.
d.Lead Alloy poor corrosion resistance
e.Improper charge and discharge cycle ratio
f.Electrolyte density and temperature is too high or too low, liquid level is not high enough.
g.Virtual welding and false welding, plate falling off.
h.Plate acidification
j.Charge and discharge current is too large.
1.10 Battery liquid leakage
1.10.1 Fault phenomenon
Common leakage phenomenon: first, the sealing between the lid and the container is not good or due to collision, the sealing glue cracking caused leakage; second, the cap valve seepage acid leakage; third, the seepage acid leakage at the terminal end; fourth, the seepage acid leakage in other parts.
1.10.2 Check and handling of faults
First do the appearance examination, find out the acid leakage site. Take the cover to see if there is any trace of acid leakage around the safety valve, and then open the safety valve to see if there is any flowing electrolyte inside the battery. After the completion of the above work, if no abnormality is found, the air tightness test should be done (put it into the water to inflate and pressurize, and observe whether the battery has bubbles coming out,if there’s bubbles, it indicates that there is acid leakage). Finally, during the charging process, observe whether there is a flowing electrolyte. If there is, it indicates the reason is from production. In the charging process if there is a flow of electrolyte, it should be drained.
1.11 The battery won't charge
1.11.1 Fault phenomenon
First check whether the connection of the charging loop is reliable, check whether the connection and plug contact is intact, carefully check whether the socket and plug have "spark" burning arc phenomenon, whether there is no line damage broken line, etc.
Check whether the charger is damaged and whether the charging parameters meet the requirements: that is, the initial charging current reaches 1.6-2.5A/pc; The maximum charging voltage reaches 14.8-14.9V/ pc, the charging float charging conversion current reaches 0.3-0.4A/pc, and the floating charging voltage reaches 14.0-14.4V/ pc.
Check whether there is a dry inside the battery, that is, whether the battery is seriously short of liquid.
Plates should also be checked whether there is irreversible sulfation. The irreversible sulfation of the plate can be determined by measuring the change of the terminal voltage. When charging, the battery voltage rises particularly fast, some single cell voltage is particularly high, beyond the normal value a lot; when discharging,the discharge voltage drops particularly fast, the battery does not have capacity or little capacity. If the above situation occurs, it can be judged that the battery has irreversible sulfation.
1.11.2 Check and handling of faults
First connect the charging loop firmly, if the charger is abnormal it should be replaced. Dry batteries should be supplemented with DM water or 1.050 sulfuric acid for maintenance, charging, discharge to restore battery capacity. If irreversible sulfation is found, equalized charging should be performed to restore capacity. The maintenance and charging of the dry battery after adding liquid should control the maximum current of 1.8A, charging for 10-15 hours, and it’s better the voltage of the three batteries are above 13.4V/pc. If the voltage difference between the cells is greater than 0.3V, the cells have experienced asynchronous irreversible sulphation. For irreversibly sulfated batteries, the whole set of batteries needs to be replaced or activated.
1.12 Battery deformation
1.12.1 Fault phenomenon
Battery deformation is not suddenly occurs, there is a process. The battery enters the high voltage charging area when charging to about 80% of the capacity. At this time, the oxygen emerges first on the positive plate, and the oxygen passes through the hole of the separator to the negative electrode, and conducts the oxygen resurrection reaction on the negative plate:
2Pb+O2=2PbO+heat
PbO+H2SO4=PbSO4+H2O+heat
Heat is generated during the reaction, and when the charging capacity reaches 90%, the oxygen rate increases, and the anode begins to produce hydrogen. The increase of a large amount of gas makes the internal pressure of the battery exceed the opening valve pressure, the safety valve opens, the gas escapes, and ultimately shows water loss.
2H2O=2H2↑+O2↑
As the number of battery cycles increases, the water gradually decreases, and the battery appears in the following situation:
a. The oxygen "channel" becomes unblocked, and the oxygen produced by the positive electrode easily reaches the negative electrode through the "channel".
b. Heat capacity is reduced, in the largest heat capacity in the battery is water, when water loss, the battery heat capacity is greatly reduced, the heat generated makes the battery temperature rise very quickly.
c. Due to the shrinkage of the glass fiber separator in the battery after water loss, the adhesion to the positive and negative plate becomes worse, the internal resistance increases, and the heat generation in the process of charge and discharge increases. After the above process, the heat generated inside the battery can only go through the battery container for heat dissipation, if the heat dissipation amount is less than the heat generation, that is, the temperature rise phenomenon. Temperature rise, make the battery precipitation gas over the potential reduction, precipitation gas volume increase, a large amount of positive oxygen go through the "channel", in the negative electrode surface reaction, emit a lot of heat, make the temperature to rise rapidly, forming a vicious cycle, namely the so-called "thermal runaway", the final temperature reached above 80℃, that is, deformation.
1.12.2 Check and handling of faults
When a group of batteries (3 pcs) deform at the same time, do the voltage check first. If the voltage is basically normal, the single cell voltage should also be measured to determine whether it is short circuit or not.
No short circuit indicates that the deformation is caused by "thermal runaway" caused by overcharging. The charging parameters of the charger should be checked emphatically. High voltage (higher than 44.7V) without overcharging protection or low trickle conversion point current (the battery conversion current of lead-calcium tin aluminum alloy is generally 0.025-0.03C 2A; the battery conversion current of lead-antimony alloy is 0.03-0.04C 2A, and the charger needs to be replaced).
In a group of 3 batteries, only 1 or 2 of them are deformed, which has the following possibility: (1) The battery charge is inconsistent, and some batteries are overcharged during charging, resulting in deformation. The cause of inconsistent charge may be short circuit of single cell, or the user may test the battery discharge or self-discharge, etc. (2) some batteries appear irreversible sulphate plate, internal resistance increases, charging heating to deformation; (3) When some batteries are connected by the reverse pole causes charging heat to deformation. Check the discharge capacity and self-discharge characteristics of the undeformed battery. If no abnormality occurs, the battery is not faulty.
The measures to solve the battery deformation are as below:
▲ Ensure that as much liquid as possible under the premise of no leakage, to extend or avoid the generation of "thermal runaway";
▲ Avoid internal short circuit or micro short circuit, and with micro short circuit tendency;
▲ In the process of use,it should prevent the occurrence of overdischarge, do full power storage;
▲ Strictly check the charger, without serious overcharging phenomenon.
▲ Ensure good heat dissipation of batteries when charging at high temperatures. Cooling measures or reducing the charging time should be taken, otherwise the charging should be stopped.
1.13 The voltage of the new battery drops rapidly
1.13.1 Fault phenomenon
The voltage drops quickly when the new battery is loaded and starts
1.13.2 Check and handling of faults
Check whether the voltage displayed on the meter is consistent with the battery capacity.
If the voltage shown by the meter and battery capacity does not conform to the above table, it needs to adjust it.
Check whether the battery connection cable is reliable, whether there is short circuit and unreliable connection. If there is, exclude it.
Check whether the starting and running current of the electric vehicle is too large. If it is too large (the starting current is above 15A and the running current is above 6A), the current limit value of the controller should be adjusted or the motor should be inspected and repaired.
1.14 The battery group is "unbalanced"
1.14.1 Fault phenomenon
The balance of series batteries is a worldwide problem, there will always be "backward" batteries in the process of use. The reasons are various, there are production reasons, but also the reasons of raw materials and use of the reasons.
1.14.2 Check and handling of faults
The battery is first charged for general maintenance and then discharged with a 2-hour rate current. The voltage of the battery is measured constantly during the discharge process, and the "backward" battery with insufficient discharge capacity is selected to be treated. First add 1.050 dilute sulfuric acid to just see the presence of flowing electrolyte, and then continue charging for 12-15 hours. Note that the battery temperature should not exceed 50℃ when charging. After charging, let it stand for 0.5-4 hours, and discharge it again at a 2-hour rate. During the discharge process, the value of the single cell voltage is measured. If the discharge time is not up to the standard or the single cell voltage is 1.6V, the discharge time is larger than the normal single cell battery (the difference is more than 5 minutes for three months, more than 8 minutes for 6 months, more than 10 minutes for 9 months). 13 months difference of more than 15 minutes), it is necessary to repeat the above charging and discharging procedures until it meets the requirements.
If repeated charging and discharging cycle, the battery capacity does not rise significantly or is still about 0V low voltage, the battery generally has a short circuit, or the active material serious fall off ,softening, serious irreversible sulphate, serious sulphation can be activated, other damage should be treated to be scrapped. the battery meeting the requirements can continue to use, it should be in constant voltage of 15V/battery charging conditions, drain the flow of electrolyte, wipe the battery surface, install the cap valve, bond the cover with PVC (or chloroform) adhesive.
2. Anatomy and analysis
When the lead battery test ends or the battery fails and fault cannot be eliminated, the battery needs to be dissected for observation and analysis. The steps are as follows:
2.1 Appearance check: Check whether there’s damage and cracks of the battery containers.
2.2 Measure the electrolyte density value, battery terminal voltage and each single cell voltage.
2.3 Check the condition of the battery pole and Lead strap.
3. Anatomical observation
3.1 Put the rubber-case battery into a higher temperature environment to soften the sealer, use a knife to pick out the sealer, saw off the connection bar with an iron saw, pull out each plate group with an iron hook and put it into the iron tray.
3.2 For the plastic-case battery, saw the battery along the heat seal of the case and cover with an iron saw. After observing whether the wall welding joint has virtual welding, false welding and fracture, and the connection between the pole and the end column, saw the wall welding joint with an iron saw, pulled out each plate group, and put it into the iron tray.
3.3 Observe the condition of the plate group, whether there is a lack of separator, whether the lead strap is broken, the connection condition between the lead strap and the lug of the plate, whether there are falling plates and false welding phenomenon. Observe whether the connection condition between the pole and the lead strap, the pole and the end column is broken or not, and whether there is any foreign body in the plate group.
3.4 Observe whether there’s short circuit connection phenomenon on the side and bottom of the plate group and the position of the separator in the plate group and whether the edge of the separator is damaged.
3.5 Observe the electrolyte status in the battery case, the deposition status of active substances, whether there is foreign matter in the case, and whether there is cracking, damage, and communication between cells in the middle partition of the battery case.
3.6 After completing the above observation, use an iron saw to cut the joint between the plate and the plate strap, and check the condition of the positive plate, negative plate and separator one by one.
3.7 Observe whether the four frames of the positive plate are broken, the plate surface condition, the active material shedding condition, the corrosion and fracture of small grid ribs and whether the plate is bent, etc.
3.8 For the tubular positive plate, observe whether the spine is damaged, whether the spine is drop from gauntlet, whether the bottom bar is falling off, whether the lead strap is broken, whether the active material in the gauntlet is sinking, etc.
3.9 Observe the surface condition of the negative plate, whether there is any sign of sulfation, whether the active material shrinkage and hardening, whether there is expansion, accumulation and shedding phenomenon.
3.10 Observe the corrosion degree of each separator, whether there is damage, fracture, corner drop, perforation phenomenon, when observing the separator, clean the separator with water and carefully observe.
4. Analysis record
After the battery anatomy observation, record the observation results, analyze the reasons of affecting the battery performance and the test termination, and put forward the battery anatomy analysis opinions.
