Campbell Scientific PS200/CH200 12 V Charging Regulators - Manual (Page 57)

PS200/CH200 12 V Charging Regulators
7. Charging Details
7.1 Charging Algorithm
The PS200/CH200 offers both Continuous and Solar charging inputs. The
Continuous charging input has a user adjustable input current limit with a
maximum (default) value of 1.1 A DC to help protect AC/AC transformers and
AC/DC converters. The 3.6 ADC typical current limit of the PS200/CH200
Solar charging input is well suited for 70 W solar panels. Typical Continuous
charging inputs would be AC/AC transformers or AC/DC converters in which
a charge voltage is continuously applied except for line power outages. When
powered from a Continuous charging input, the PS200/CH200 tries to maintain
the battery at a float charge voltage, which can continue indefinitely without
overcharging the battery.
When powered from a Solar charging input, the PS200/CH200 utilizes a two-
step constant voltage charging algorithm, which is the preferred method for
rapidly charging VRLA batteries
1 . When powered from the Solar charging
input, the battery charge deficit (Qloss) is compared to the specified battery
capacity in order to determine if aggressive cycle charging is necessary. Cycle
charging is then utilized if Qloss is determined to be greater than 20% of the
battery capacity. Upon detection that the battery is near full charge, the
constant voltage charging level is reduced from the aggressive cycle charging
voltage to the non-aggressive float charge voltage to prevent overcharging and
unwanted gassing of the battery.
In the PS200, the battery capacity is set to 7 Ah hours at the factory, whereas
the battery capacity is left at the default value of 0 Ah in the CH200 where the
user provides the battery. If the battery capacity is left at the default value of
zero, then Qloss always equals 0, which disables cycle charging.
Consequently, CH200 users must enter in the battery capacity in order to
enable the aggressive cycle charging capability of the two-step constant voltage
charging algorithm.
Discharged VRLA batteries can initially accept large charging currents, often
resulting in the charger being unable to initially maintain a constant voltage
because of current limiting by the charge source or the charger itself. As a
result, a typical two-step constant voltage charging cycle usually consists of
three distinct stages; a current limited charge stage, a constant cycle voltage
charge stage, and a constant float voltage charge stage, as illustrated in
FIGURE 7-1. The current limited stage and/or the constant cycle charge
voltage stage may not occur if the battery size is small relative to the current
capability of the charge source, or if the battery is near full charge at the
beginning of a charge cycle.
Normally cycle charging terminates and float charging begins when Qloss has
been reduced to zero. Two exceptions exist, both of which help prevent
overcharging of the battery. One exception to this normal cycle to float
transition occurs if cycle charging has been on-going for 8 hours without
interruption, indicating some sort of battery problem. In this case cycle charge
will be terminated and Qloss will be zeroed. The other exception to the normal
cycle to float transition when Qloss has been reduced to zero occurs if during
cycle charging the battery charge current is reduced to below C/100, where C is
the user entered battery capacity. This condition indicates the charger is trying
to aggressively cycle charge a fully charged battery, perhaps because a new
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