ABB Pulsar Edge, Product Manual

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Appendix C: Battery Functions
Float Mode
Float mode is the default operation mode of the power system. The system voltage, while in float
mode, is determined by the configuration parameter Rectifier Float Set point (fsp) and may be
adjusted by the Battery Thermal Compensation circuit, if active. No individual adjustment of plant
rectifiers is necessary and load sharing among plant rectifiers is automatic in all plant modes and will
take effect within several seconds of a new rectifier being added to the system.
The Rectifier Float Set point should be set per the battery manufacturer's recommendations. Note that
the actual Rectifier Float Set point measured on the plant may differ from the value set by the user if
battery thermal compensation (STC) is enabled.
Slope Thermal Compensation
The Pulsar Edge has a flexible battery Thermal Compensation feature which provides voltage
compensation from that level established by the Plant Float Set
- Point (fsp) or Boost Set - Point (bsp),
dependent on the highest temperature monitored by the QS873A VT - Probes attached to the system
batteries. Thermal Compensation can lower or raise the system bus voltage from the Float Set Point
voltage. For monitored battery temperatures above an ideal battery temperature the controller can
lower the system voltage per programmed linear curve. Lowering the plant voltage helps keep the
batteries at their optimum state of charge while protecting them from thermal runaway. For monitored
battery temperatures lower than the ideal battery temperature the controller can raise the system
voltage per programmed linear curve. Raising the system voltage helps keep the batteries at their
optimum state of charge.
Increasing the system voltage with decreases in battery temperature also causes more current to flow
into the batteries which results in electrolysis of the water in the batteries. This reaction is exothermic
and also serves to keep batteries warm. Thermal Compensation is generally used in systems utilizing
sealed or valve
- regulated maintenance free batteries. Thermal Compensation is automatically enabled
from the factory when Valve - Regulated Lead Acid batteries are the system battery type.
Thermal runaway is a complex sealed battery phenomenon where, for one or more of a number of
reasons, one or more cells in a string may be unable to dissipate the internal heat generated by their
charging current and as a result will experience an increase in internal temperature. By having the
controller lower the float voltage as the battery temperature increases, system tries to keep the float
current lower to a point where destructive battery behavior can be avoided. If cell failure is imminent
and the battery temperature continues to rise above the threshold configured for Battery Thermal
Voltage Step Down Temperature, the controller has a feature that will force the system DC bus voltage
to drop in a single step to a level which should keep the remaining cells in the string from overcharging
and being damaged. The following figure provides a graphical view of the Pulsar Edge
’ s Battery
Thermal Compensation feature and the relationship of its various set points.