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3.2.3 Normal Operation Charging
The following voltage settings during charge are optimum values when
the battery is not heavily undercharged or overcharged. A good indicator
to check is the percent of overcharge per cycle (charging factor) within
a long period of operation (a month to a year). Deviations from the
charging factors given below require that the charge settings and the
overall system operation be checked again:
•
Charging factor is >107% for Stand-alone systems with MDDoD
<5%
•
Charging factor is 105% to 110% for Stand-alone systems with
MDDoD >5%
•
Charging factor is 104% to 108% for Hybrid systems.
3.2.3.1 Settings for Stand-Alone Systems
Settings shall be adjusted according to battery temperature.
Temperatures are averaged over one month:
•
For systems with oversized PV array and low MDDoD (<5%),
use lower settings (Sec. 3.3).
•
Functional equalizing charges are required in periods with marginal
“Array to Load ratio”, less than 1.3x times. Typical functional
equalizing would be performed 1 to 6 times per year.
3.2.3.2 Settings for Hybrid Systems
Daily charge after discharge:
•
Only a constant voltage controller is permitted.
•
The absorption voltage setting shall be adjusted according to the
batteries averaged temperature over one month:
•
The absorption time setting can be selected between 4 to 12
hours. The frequency of the functional equalizing charge shall be
adjusted accordingly:
•
Functional equalizing frequency
A functional equalizing last 24 hours with voltage settings the same
above.
3.2.2 Equalizing Charge
3.2.2.1 Functional Equalizing
To avoid permanent capacity loss and acid stratification in cycling
operation the goal is to achieve a complete recharge (100% SoC) after
every discharge. Capacity loss and acid stratification will threaten the
battery’s state of health.
•
In Stand-alone Systems this is not always possible as in Stand-
alone applications where the RE source depends on the weather
conditions causing the load to exceed the designed limitations.
In this case proper “Array to Load ratios” (as given in paragraph
3.1) are critical for the life expectancy of the battery to be achieved
•
For Hybrid Systems with diesel generators (mainly telecom
hybrid systems), the charging source is always available but
the boost charging time is restricted to favor a more efficient
utilization of the diesel.
In both cases, a scheduled functional equalizing charge shall be
performed at regular intervals (Sec. 3.2.3) to protect the battery
from acid stratification, sulphation and loss of capacity.
Functional Equalizing frequency is adjusted according to the charge
deficit. The less complete the daily recharge is, the more frequently
an equalizing charge will be required (see Normal operation
charging)
•
The charge duration is fixed.
•
The values of the voltage settings are the same as those for a
normal recharge
3.2.2.2 Corrective Equalizing
Equalizing charges are also required after incidents of excessive
stress for the battery (deep discharges with inadequate charges) or
when the individual cell or block voltages show excessive deviation
from the average (lagging cells and sulphation problems). Should
the voltage in individual cells/blocks deviate from the average value
more than the following limits, perform an equalizing charge.
Deviation limits
Corrective Equalizing is performed as a Full Charge as outlined
in section 3.2.1. If the voltages are still out of the limits, contact
Discover
®
Engineering or Discover
®
Customer Service or your
servicing Discover
®
dealer. A service contract with an authorized
Discover
®
factory warehouse or dealer is recommended.
Battery status
2V Cells
6V Blocks
12V Blocks
Floating
-0.1V - +0.2V
-0.17V - +0.35V -0.25V - +0.50V
Regulation
Voltage
-0.20V - +0.35V
-0.35V - +0.60V
-0.50V - +0.90V
During discharge
when the DoD
is between 5%
and 25%
+/- 0.04V
+/- 0.06V
+/- 0.08V
During discharge
when the DoD
is between 25%
and 60%
+/- 0.06V
+/- 0.09V
+/- 0.12V
At rest at least
16 hours after
a Functional
Equalizing
Charge
+/- 0.025V
+/- 0.04V
+/- 0.06V
Controller
type
Setting
-20°C to
0°C
0°C to
15°C
15°C to
35°C
>35°C
Constant
Voltage
One Step
Voltage
Regulation
2.50VPC
2.45VPC
2.40VPC
2.35VPC
Constant
Voltage
Two Step
Absorption
time up to
2 hrs per
day
2.55VPC
2.50VPC
2.45VPC
2.40VPC
Float
2.45VPC
2.40VPC
2.35VPC
2.30VPC
On-Off
High
Voltage
2.55VPC
2.50VPC
2.45VPC
2.40VPC
Low
Voltage
2.35VPC
2.30VPC
2.30VPC
2.25VPC
Absorption
Time
4-6
hours
6-8
hours
8-10
hours
10-12
hours
Equilizing every
7 cycles
14 cycles
21 cycles
28 cycles
If one cycle is one day
1 weeks
2 weeks
3 weeks
4 weeks
Temperature
-20°C to 0°C
0°C to 15°C 15°C to 35°C
>35°C
Absorption
Voltage
2.50VPC
2.45VPC
2.40VPC
2.35VPC
