tank’s capacity does not vary over time.
None of these analogies apply to batteries. Lead-acid batteries can accept higher charge currents when they are nearly empty,
but must be charged more slowly when they are nearly full because then they will not readily accept the charge. Batteries need
to be frequently fully charged. If a battery is allowed to operate consistently at a low charge level, its capacity to hold charge
decreases over time. This means that a battery needs to be fully charged every now and then for the proper maintenance of its
capacity. In solar applications, this sometimes cannot be achieved in the course of a single day, depending on sunshine and
energy usage.
Sometimes a generator is used instead of sunlight to charge the battery at a high current for one or two hours each day. This can
easily shorten the life of lead-acid batteries, which cannot get fully charged in two hours even with a very powerful generator. If
only charged with very high currents over a short time, a battery’s charge capacity will decline over time. A “hybrid” generator-
solar system would be preferable with a strategy of using the generator to provide a fast charge early in the morning, when the
battery is at its lowest charge level, and stop when the battery can no longer accept high charging currents. By the time the sun
is high enough, the solar panel can take over the charging at a lower current for the following six to nine hours. Alternatively, a
surplus of solar panels can accomplish something similar, but that means the peak solar power in the afternoon, when batteries
are accepting less current, may not be used. To overcome this, plan to use heavier loads, such as laundry, dish washing or well
pumping, during the mid afternoon, when batteries accept less solar energy.
6.2 Specifically how solar chargers, including the SC-2030 charge batteries
The following charging description applies when the SC-2030 Solar charger is connected with the TM-2030. If for some reason
the TM-2030 is not connected, it uses a basic charging procedure, to be described in section 6.3.
This discussion refers to 12V systems—for 24V systems multiply voltages by two.
To charge batteries, a charger supplies electrical energy to the battery with a certain "voltage." "Volts" is a measure of how hard
the charger is attempting to push the energy (electrons) into the battery. The battery always tends to resist the tendency to push
the electrons in—the voltage of the charger must be high enough to overcome the resisting force of the battery. This is a little
like pushing water into a pipe which is under pressure—enough force must be provided to push it in or it will not go. The
"current" or "amperes" is a measure of how much (charge) energy is actually flowing in. The actual flow (“amps” or amperes)
depends on two factors: how hard the charger is pushing (voltage) and how much the battery is resisting.
When batteries are at a lower state of charge they do not push back very hard, and the battery will easily absorb all the charge
(amperes) that the charger can supply. This is called the "bulk" stage of charging, and the "voltage" from the charger during
charging will be below 14 volts or so. This is when most of the charge can go into the battery, and is the simplest part of the
charging process; usually the batteries will be able to absorb all the energy the charger is capable of delivering.
When the batteries reach about 85% full, the job of the charger gets more difficult. The batteries begin to resist more, and
absorb amps at a lower rate, meaning that it takes a longer time to do the rest of the charging. One might say, "why bother, then
to go beyond 85% full? Wouldn't this make the job easy on the charger? Just always operate the batteries from 55%-85%
charged." Well, yes it would, but the reason this is not a satisfactory strategy for lead acid batteries is that if you don't fully
charge them regularly, it makes it harder in the future to charge them as much. It is remarkable how often even authoritative
sources on lead acid battery charging repeat the phrase that "lead acid batteries do not have memory." Lead acid batteries DO
have a memory—if you do not fully charge them, they will remember that, and if this is repeated often their capacity will
gradually "walk down" as is correctly described in charging information from the Concorde battery company.
This presents a challenge to solar charging— because the solar day starts to end as the batteries become more resistant. This
can result in a battery that is not fully charged when the day ends. It is frequently observed that batteries being charged only by
solar tend to lose capacity to hold energy— described as batteries becoming “sulfated”. This conveys the fact that the lead
sulfate, which is the byproduct of discharging gets more difficult to convert back to fully charged lead and sulfuric acid if it sits
