18/09/2003
HESC-UPS Manual
Tri-M Engineering
Tel:
800.665.5600, 604.945.9565
1407 Kebet Way, Unit 100
Fax:
604.945.95
Port Coquitlam, BC, V3C 6L3
E-mail:
Canada
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Section 9 : Battery Charging Algorithms and Strategies
A. Sealed Lead Acid, SLA
1. Single Stage Charging
Many SLA batteries require only a single stage of charging. In single stage charging, the battery is charged with
constant current until the battery voltage approaches the "float" voltage. The float voltage is the voltage across
the battery when a small trickle current is used to maintain the full charge state of the SLA battery. The float
voltage is very close to the "open circuit" voltage of the HESC charger output, and in most instances, is an
acceptable method of checking the HESC float voltage setting. When the battery voltage rises close to the float
voltage the charger transitions from constant current to constant voltage charging. The transition from constant
current to constant voltage is not an instantaneous change, but gradual as the net potential difference between
the HESC charger output and the battery voltage is not sufficient to maintain the current in constant current mode.
The following is an example charging parameters, and charge termination methods that are suitable for SLA
batteries requiring single stage charging.
Ex. 12V SLA (6 cell), 4.5amp-hour, ambient temperature conditions -20C to 35C
Table 12, SLA Single Stage Charging Set-up
EEprom Enable Values EEprom Variable Values
Description
BattTempMaxEn = 1
BattTempMax = 3182*
Terminates charging if battery temperature above
BattTempMax.
Set for 45C
BattVmaxEn = 1
BattVmax = 13900
Terminates charging if battery voltage above BattVmaxDef.
Set for 13.9V
BattTempCompEn = 1
BattTempComp = 18
Compensates the BattVDef voltage for the ambient
temperature. Compensation is in mV starting at 298.2K (25C).
N/A
BattVDef = 13700
"Float" voltage set-up. Set for 13.7 volts
N/A
BattIDef = 2500
Maximum charge current. Set for 2500mA
CHCycleMax = 1
Set for single stage charging
BattAutoStartEn = 1
Charging auto starts when the HESC is reset (main power is
removed then re-applied), or when a new battery is inserted
TermEn = 1
Charge termination is enabled
BattIsolateEn = 1
HESC de-activates the battery enable line (BE) after the power
supply enters the shutdown mode.
Then = 1
Thermistor monitoring enabled
*Temperature in 0.1degK, absolute zero (0K) = -273.2C
2. Dual Stage Charging
A disadvantage of single stage charging is the charging current drops as the battery voltage approaches the float
voltage. A two stage charging algorithm maintains full charging current throughout the first stage, and switches to
constant float voltage charging in the second stage. The termination of stage 1 charging is when the battery
voltage reaches the stage one BattVmax voltage. BattVmax is usually higher than the float voltage (2.45V/cell vs
2.3V/cell). Since the HESC is required to operate in constant current mode throughout stage one, the BattVDef
has to be set higher than BattVMax. In theory, BattVDef could be set to its maximum, but this is not a good
practice. A better practice is to set BattVDef just high enough to allow the HESC to remain in constant current
mode throughout stage one charging.
