Bogart Engineering SC-2030 Technical Manual

Bogart Engineering
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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 "absorption" state the SC-2030 then increases voltage (while regulating current) to attempt to put more
charge at the end when the battery is becoming extra resistant so as to attain the specified overcharge amount. The
overcharge percentage, maximum voltage, and maximum permitted current are all values that can be programmed into the
TM-2030.
The effect of temperature on charging: The ideal temperature for a lead acid battery is often considered to be
about 25 degrees C (77 degrees F). When batteries are cold, the charging process is slower, so they take longer to charge.
The gassing voltage of the battery increases with lower temperature—and therefore the recommended "absorption"
voltage should rise as temperature goes below the usual reference temperature of 25 degrees C (77 degrees F). If the
battery temperature varies much, the charger should have the capability to adjust its voltage to temperature, especially for
sealed AGM or gel types.
6.3 Description and graph of exact SC-2030 charging profiles
Standalone operation-without the TM-2030: With the TM-2030 not connected, there are only two charging
selections available (by two jumpers you set on the SC-2030 circuit board.) They allow choice for "AGM or liquid
electrolyte" and "12 or 24V" system. These are intended to be for "backup" charging if for any reason the TM-2030 is not
connected. When the TM-2030 is connected, these values are ignored.
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