The Bulk Charge Step
Originally Posted by mcbarsranch
How long does your charger take on each stage during charging?
When a charge source is first applied to a well discharged battery, charge current begins to flow, typically at the maximum rate of the charge source. If a true 40 Amp charger is connected to an 8D battery which is completely discharged, about 40 Amps of charge current would flow for some period of time. Because most of the charge is delivered at the maximum charger rate, the first step of the charge cycle is called the bulk charge step. NOTE: During the bulk step, battery voltage will steadily rise.
The Start of the Absorption Step
At the instant battery voltage has risen to the maximum allowable voltage of the charge source, current through the battery begins to decline. This simultaneous event of reaching maximum voltage and the start of current decline marks the beginning of the absorption step.
For instance, if the 40 Amp charger is set to 14.4 Volts, then when battery voltage has risen to 14.4 Volts, the charger will now hold the voltage constant. Current through the battery will begin to decline. NOTE: The charger, (or alternator), is not limiting the current at this point. The battery is `absorbing' all it can at the voltage setpoint.
The End of the Absorption Step
The absorption step should continue until current through the battery declines to about 2% of battery capacity in Amp-hours as mentioned above. Without knowing what the current is through the battery, you can't know when it's full. Just because that fancy charger, (or inverter/charger), has kicked out to float is no sign that the battery is full ...there is no charger on the market that measures battery current!
It's a given, then, that you need to measure battery current to know when the battery is full. With a battery current meter, you can discover some very interesting details about the charge process. For instance, you can discover that once the charger voltage limit is reached, battery current begins to decline. If the current decline is rapid, either the batteries are nearly full, or they are NO GOOD! If the current decline is slow, then either the charge source has more output than the batteries can reasonably absorb, or the batteries are NO GOOD! Here's where Amp-hour instrumentation is particularly valuable.
Given enough time at the absorption voltage, charge current will decline to a steady-state value, that is, a low current that either stays constant, or declines very little. At the point where charge current has gone as low as it is going to, then the batteries are truly full. While 2% of Ah rating is close, good batteries will reach a steady state current at less than 1% of Ah rating.
The Float Step
Once a battery is full, a lower voltage should be applied that will maintain the full charge. Depending on the type of battery, (liquid, gel), and the age of the battery, 13.4 - 13.8 Volts is appropriate as a float voltage.