Failure modes and repair methods of lead-acid batteries (3/3)

3. Repair method of premature loss of capacity (PCL)


3.1 Characteristics of premature loss of capacity

When the low sb or Pb Ca alloy is grid alloy, the capacity of the battery will drop suddenly in the initial use period (about 20 cycles), which will lead to the failure of the battery. Almost every cycle of battery capacity will be reduced by 5%, the rate of capacity decline is faster and earlier.

In the past few years, lead calcium alloy series of batteries often inexplicably appear several battery capacity decline. Analysis of the positive plate did not soften, but the positive plate capacity is very low.


3.2 Find solutions to the causes of this phenomenon

1)  The content of tin in the positive plate. For deep cycle batteries, the content of tin is 1.5% ~ 2%.

2)  Increase assembly pressure.

3)  The content of acid in electrolyte should not be too high.


3.3 Pay attention in use

1)  Avoid continuous low initial charging current;

2)  Reduce deep discharge;

3)  Avoid overcharging too much;

4)  Do not increase battery capacity by excessive utilization of active substances.


3.4 recovery of batteries with early capacity loss

1)  Firstly, the initial charging current should be increased to 0.3C ~ 0.5c, and then small current should be used to make up the charging;

2)  Secondly, the fully charged battery should be stored at 40 ℃~ 60 and discharged to 0V with a small current less than 0.05c. When the battery voltage reaches half of the nominal voltage, the discharge will be slow. The capacity of the battery can be recovered after several times.

 

3.5 precautions

Be sure to identify whether the battery occurred in the first 20 cycles. If the capacity of the battery decreases in the middle and later period, this method can only destroy the positive plate of the battery and cause the positive plate to soften.

Lead calcium alloy series of batteries often inexplicably appear several battery capacity decline, the main reason is caused by battery imbalance, lead calcium alloy series battery sufficient voltage is high, generally 12 V battery charging voltage is greater than 16 v. When the voltage of charger is too low, it is easy to cause battery imbalance. This phenomenon occurs in this way. When a group of batteries are used together, the self discharge of each cell of the battery cannot be absolutely equal. The battery with a little larger self discharge can not be fully charged with constant voltage charger each time. The cell with insufficient power does not have gas evolution reaction, and the relative area of electrode plate contacting with the electrolyte is large, so the self discharge is large. The cell with small self discharge can be fully charged each time. When the cell is overcharged a little after sufficient power, the gas evolution reaction will occur and gas will be generated. The electrode plate contacts with the electrolytic liquid level and the self discharge will be reduced. At the same time, the charging voltage will increase and the charger will be turned off. Results the self discharge of cells with small self discharge and high voltage becomes smaller and smaller, and can be fully charged each time. However, the grid with large self discharge discharge is getting larger and larger, and it can not be fully charged every time. Moreover, the smaller the power consumption is, the vulcanization and failure will occur if the battery is not sufficient for a long time, If the constant voltage is too high, the battery will lose control of heat. The best way is to use multi-stage charger with multiple current and multi voltage. At the end of charging, a small current with high voltage and low current should be charged for a long time to balance the battery power

 

4. Overcharge Repair

Overcharging often requires large current and high voltage, which will form a strong side reaction and damage the positive plate of the battery, as well as form the water loss of the battery. How to achieve overcharge repair? Now we have found a very effective method - pulse method. The basic principles are as follows:

High voltage and high current pulse is used to overcome the decline of battery acceptance caused by various reasons. Due to the pulse form, after the high current pulse disappears, the depolarization ability of the battery itself (or additional conditions) will not form serious side effects. With the birth of this method of pulse overcharge repair, no damage overcharge can be realized. This kind of charger has achieved excellent results. After several years of verification test, this method has greatly extended the cycle life of lead-acid battery.


(From magazine UPS Application - April 29, 2019)



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