and sulphation problems).
Should the voltage in individual cells deviate from the average value more than the following limits, perform an
equalizing charge:
Battery state
2V cells
at floating, after the first 6 months of operation
-0.1V / +0.2V
at the end of the normal charge, while current is stable, after the first
6 months of operation
-0.2V / +0.35V
during discharge, while DoD is between 5 and 20%
± 0.04V
during discharge, while DoD is between 20 and 60%
± 0.06V
at rest, 24h after a Functional Equalizing charge
± 0.025V
Corrective Equalizing is performed as a Full Charge in paragraph 3.2.1.
If the voltages are still out of the limits, Systems Sunlight Customer Service should be called.
A service contract with Systems Sunlight S.A. is recommended.
3.2.3. Normal operation charging
The following charging voltage settings are optimum values, so the battery is not heavily undercharged or
overcharged. A good indicator to check this is the percentage of overcharge per cycle (charging factor) within a
long period of operation (a month to a year). Deviations from the charging factors given here, prompt to check
the charging settings and the overall system operation again:
>107% for Stand-alone systems with Maximum Daily DOD less than 5%
105% to 110% for Stand-alone systems with MDDOD more than 5%
104% to 107% for Hybrid systems.
3.2.3.1. Settings for Stand-alone systems
The settings shall be adjusted according to battery temperature. Temperatures are averaged over one month:
Controller type
Setting
-20 to 0°C
0 to 15°C
15 to 35°C
>35°C
Constant Voltage – one
step
Vr
2,50V
2,45V
2,40V
2,35V
Constant Voltage – two
steps
absorption
maximum 2 h per day
2,55V
2,50V
2,45V
2,40V
float
2,45V
2,40V
2,35V
2,30V
On-off
High voltage (Vr)
2,55V
2,50V
2,45V
2,40V
Low voltage (Vrr)
2,35V
2,30V
2,30V
2,25V
For systems with oversized PV array and low MDDOD (<5%), use lower settings (see paragraph 3.3).
Functional equalizing charges are required in periods with marginal “Array to Load ratio”, less than 1.3. Typical
frequency is 1 to 6 times per year.
3.2.3.2. Settings for Hybrid systems
The settings shall be adjusted according to the battery temperature. Temperatures are averaged over one month.
The duration for the absorption phase per cycle can be within 4 to 12 hours. The frequency of the Functional
Equalizing charges is adjusted accordingly.
Controller type
Setting
-20 to 0°C
0 to 15°C
15 to 35°C
>35°C
Constant Voltage
Absorption voltage
2,50V
2,45V
2,40V
2,35V
Functional equalizing frequency
Absorption time
4-6h
6-8h
8-10h
10-12h
Equalizing every
7 cycles
14 cycles
21 cycles
28 cycles
if one cycle is one day
one week
two weeks
three weeks
four weeks
A functional equalizing lasts 24 hours with voltage settings the same as above.
3.3. Operation at no or very low load
When there is little or no load connected to the system for long periods (more than 1 month) while the battery
remains connected, the normal charging settings in paragraph 3.2 are too high and result in unwanted
overcharging. The same is true for Stand-alone systems with oversized PV array and very low MDDOD (<5%) like
in remote Telecom transmitters.
