Routine equalization charges are vital to the performance and life of a flooded lead acid battery…
particularly in a solar, wind and less so in a micro-hydro power system. During battery discharge, sulfuric acid is consumed and soft lead sulfate crystals form on the plates. Learn more about making your battery bank last as long as possible.
If the battery remains in a partially discharged condition, the soft crystals will turn into hard crystals over time. This process, called “lead sulfation”, causes the crystals to become harder over time and more difficult to convert back to soft active materials.
Sulfation from chronic undercharging of the battery is the leading cause of battery failures in solar systems.
In addition to reducing the battery capacity, sulfate build-up (flooded lead acid and sealed batteries) is the most common cause of buckling plates and cracked grids.
Deep cycle batteries are particularly susceptible to lead sulfation. Normal bulk charging of the battery can convert the sulfate back to the soft active material if the battery is fully recharged.
However, a solar battery is seldom completely and fully recharged, so the soft lead sulfate crystals will harden over a period of time.
WHAT ARE THE ADVANTAGES OF BATTERY EQUALIZATION?
SLOW OR PREVENT SULFATE FROM BUILDING UP ON THE LEAD PLATES – Only a long controlled overcharge, or equalization, at a higher voltage can reverse the hardening sulfate crystals.
Normal charging will reduce sulfation, but to remove it, the battery must be equalized.
BALANCE THE INDIVIDUAL CELL VOLTAGES – Over time, individual cell voltages can drift apart due to slight differences in the cells. For example…in a 3 cell (6VDC) battery, if one cell is less efficient in bulk charging to a final battery voltage of 28.8 volts (2.4 volts per cell), over time, that cell might only reach 2.30 volts, while the other 2 cells charge to 2.45 volts per cell.
The overall bulk battery voltage is 7.2V, but the individual cells are higher or lower due to cell drift. Equalization cycles help make all the cells the same voltage or equalize.
MIX THE ELECTROLYTE – In flooded lead acid batteries, especially taller cells (like the Trojan 6VDC L16 or Surrette 6VDC L16), the heavier acid will fall to the bottom of the cell over time compared to the standard 6VDC golf cart battery .
This stratification (dividing between the heavier distilled water and lighter battery acid) of the electrolyte causes loss of capacity and corrosion of the lower portion of the plates.
Boiling of the electrolyte from a controlled overcharging (equalization charge) will stir and remix the distilled water and acid into the battery electrolyte.
HOW OFTEN SHOULD YOU EQUALIZE YOUR BATTERIES?
The ideal frequency of equalization charges depends on the battery type (lead-calcium, lead-antimony, etc.), the depth of discharging, battery age, temperature, and other factors. One very broad guide is to equalize flooded lead acid batteries every 1 to 3 months or every 5 to 10 deep discharges. Some batteries, such as the large L-16 type, will need more frequent equalization charges compared to a golf cart battery. The L16 tends to sulfate more quickly..
The difference in specific gravity between the highest cell and lowest cell in a battery can also indicate the need for an equalization.
Either the specific gravity or the cell voltage can be measured with the specific gravity of the electrolyte being the most accurate when deciding whether or not your battery/battery bank needs an equalization charge.
The battery manufacturer can recommend the specific gravity or voltage values for your particular battery.
SHOULD YOU EVER EQUALIZE A SEALED BATTERY?
NO, NO, NO! NEVER!!!
Sealed batteries do not tolerate equalization, could explode (in very rare cases), and cannot have any distilled water replaced (as there are no removable caps/covers) after an equalization charge.
AGM (Absorbed Glass Mat) and GEL CELL BATTERIES WILL BE DESTROYED IF OVERCHARGED.
Follow the manufacturer’s bulk/absorption charge recommendations strictly.
They are not supposed to gas (vent) and more importantly if they do, you will NOT be able to refill them with distilled water and they WILL be damaged if the voltage is allowed to go higher than the manufacturers recommendations.