Equalization and desulphation

[THIS PARAGRAPH WAS TAKEN FROM FIRST PAGE OF PRESENTATION] Battery life and restoration have become increasingly important.  The freight cost of shipping dead and permanently damaged batteries back for maintenance and replenishing customers with replacements is prohibitive.  Many misconceptions and misinformation have been disseminated about battery life and the mechanisms of degradation.  In most cases, the primary culprit is plate sulphation. The sulphation, desulphation and restoration of lead acid based batteries is widely misunderstood.

Four stage charging cycle

Four stage charging supplies constant current to battery until absorption voltage is reached (V_FSTERM).  Transition to absorption mode follows and regulates battery voltage at V_FSTERM until current decreases to I_ABTERM. Float mode follows and regulates battery voltage at V_FL.  At the user's discretion, an equalization mode can be initiated.

[I put this stuff below here for now -- but I think it's bad (redundant) to have it repeat what's already on the Basics page]

Stage 1: Constant current charging or bulk charge mode

Assuming the battery is starting in a discharged state, the charger is operating in constant current mode, where the charger current is maintained at a constant value and the battery voltage is allowed to rise as it is being recharged. Approximately 80% of battery capacity is returned in the constant current region.

Stage 2: Absorption mode

When the battery voltage reaches approximately 2.4 volts per cell, or 14.6 volts for a 12V battery, the charger voltage is held constant at this level and the battery current is allowed to reduce. It is this region where the last 20% of battery capacity is returned. This voltage level is maintained until the battery current reduces to approximately C/50 to C/100, where C is the amp-hour rating of the battery. For instance, if it is a 100 amp-hour battery, the voltage should be maintained at 2.5V per cell until the current decreases to 1-2 amps. The exact amount is not usually critical.

Stage 3: Float mode

At the point where the current is reduced to C/50 to C/100, the battery charger enters float mode. Float mode is where the voltage on the battery is maintained at approximately 2.25 volts per cell, or 13.5 volts for a 12V battery. This voltage will maintain the full charge condition in the battery without boiling our electrolyte or overcharging the battery.

Stage 4: Equalization mode

The purpose of the equalization mode is to remove the sulphation from the lead plates and to eliminate the stratification of the electrolyte. Approximately 2.5-2.6 volts per cell is applied to the battery with the charging current set to a very low value, typically less than 0.5 amp. The equalization mode may last anywhere from a few hours to over 24 hours depending upon circumstances.

For more information about equalization and desulphation, see this presentation.