around too long before recharging.
To continue the charging story, once the batteries become more resistant to charging—when the charger rises to 14.4 volts, (at
77 degrees F or 25 degrees C) liquid electrolyte batteries will begin to "gas" which means that although part of the energy is
still doing some slower charging, part of the charger energy is breaking down the electrolyte in the battery into oxygen and
hydrogen gases—and in addition a higher amount of the energy begins to go into heating the battery instead of the desirable
conversion of the chemical charging. Although the gassing does waste some energy, this turns out to be desirable in liquid
electrolyte batteries because the gas bubbles stir up the electrolyte which otherwise can stratify—because without the stirring
the heavier acid can sink to the bottom while weaker acid goes to the top causing unequal charging at the top and bottom. In
AGM batteries, the design is different, so gassing typically doesn't occur, which makes them a little more efficient.
Good solar chargers will then go into what is often called "absorb" stage—where the charger holds the voltage just above the
gassing point (voltage ideally temperature compensated). The batteries then absorb gradually less and less energy as they
further charge. Most manufactured solar chargers maintain the "absorb" voltage for a set amount of time—perhaps one to four
hours before they go into the "float" voltage of about 13.2 volts. Often the better chargers allow you to set the exact absorption
voltage, the holding time, and the exact float voltage. The float voltage is a maintenance voltage which is intended to be the
ideal voltage to keep a battery at minimum wear for the longest time once it's fully charged.
Although just maintaining the "absorb" voltage for a fixed time is not a bad way to decide when to go into "float", many battery
companies suggest that it is better to monitor the amount of current (amperes) going into the battery during this time and then
go into float based on this. There are three variations on this method:
(1) Charge above the gassing voltage until the amperes drop to a sufficiently low value, say an "ampere" value that is 1% or
0.5% of the amp hour "capacity" of the batteries.
(2) Charge until the value of amps into the batteries stops decreasing for a specified period of time—and stays at this constant
value for perhaps a couple of hours.
(3) Charge until the charger has replaced a specified percentage of charge amp hours that was last removed from the batteries
during its last discharge cycle.
These options are unusual with most solar chargers, but the first or third is possible with the SC-2030 solar charger when used
with the TM-2030 monitor. The TM-2030 measures the previous amount of discharge (typically the night before), then when
recharging requires returning 105-120% of that amount, adjustable by the user. The problem for many chargers is that they do
not measure or know the exact value of amperes or amp hours going into the batteries. They may measure the amps from the
charger going into the battery and loads together, but they don't know what percentage of this is going into the battery
compared to the loads, so these methods of observing battery amps are not available.
By returning a constant additional percentage, excess charge that is returned depends on the amount that was previously
removed. This has the effect that the "absorb" time is not always the same, but is adjusted to the previous day's usage to avoid
overcharge or undercharge. Undercharge is more common in many systems, but in applications where solar charging goes on
for days when very little drain occurs on the batteries, such as for RV’s stored in the sun, or occasionally used cabins,
measuring amp hours can avoid overcharge.
An additional method the SC-2030 uses to get in sufficient charge is that it has an (optional) finish charge stage to try to
increase the intake of current into the battery by boosting the voltage when the current has declined to a safe enough value. This
is explicitly recommended by some battery companies for liquid electrolyte batteries and recently even AGM types—but
usually not gel batteries.). If the SC-2030 is programmed to do this, after the charging current decreases to a safe value while in
