2.3. Cells in parallel strings
Valve-regulated cells may be connected in parallel to give higher current capability. In the case of parallel
connected strings, use batteries of the same capacity, design and age only with a maximum of 4 parallel strings.
If more than 4 strings are required, consult SYSTEMS SUNLIGHT S.A. The resistance of the cables in each string
must be the same, e.g. same cross-section, same length. In addition, each string should be equipped with
disconnect capabilities for maintenance and safety purposes.
2.4. Preliminary control
Check for evidence of leakage. All cells with visible defects such as cracked jars, loose terminal posts, or other
unrecoverable problems shall be rejected.
In case the surface of battery container is dirty before installation wash with soapy water only.
Carry out OCV (open circuit voltage) measurements on each individual cell battery to check their compliance
against the variation and absolute voltage criteria:
The cells’ OCV must not deviate from average more than ± 0.025 V.
The cells’ OCV must not be lower than 2.07 V.
Should not compliance noticed, consult SYSTEMS SUNLIGHT S.A..
Note: OCV of a fully charge cell is ~2,13 V. Per 10% Depth of Discharge (DOD) the voltage is reduced by ~0,025
V, for example, OCV of 2,08 V corresponds to 20% discharged cell.
2.5. Electrical connections
Ensure that the cells are installed in the correct polarity. Check that all contact surfaces are clean. If required,
clean with a brass brush/pad. You may lubricate slightly the inserts and connections with silicone grease.
Petroleum-based lubricant is not recommended.
Tighten the terminal screws, using the correct torque loading of 22 Nm.
Electrical connections to the battery and between cells on separate levels or racks should be made to minimize
mechanical strain on battery terminal posts.
For systems where the total battery voltage is measured at the controller, use oversized cables to the battery in
order to minimize the voltage drop.
Check the battery's total voltage. It should match the number of cells connected in series. If the measurement is
not as expected, recheck the connections for proper polarity.
Batteries with a nominal voltage > 75 V require an EC conformity declaration in acc. with the low voltage directive
(73/23/EEC), which confirms that the CE marking is applied to the battery. The company installing the battery is
responsible for the declaration and applying the CE marking.
For future identification, apply individual cell/unit numbers in sequence starting from one end of the battery. Also
apply identification numbers for the parallel strings.
Connect the battery to the DC power supply, with the charger switched off, battery fuses removed and the load
disconnected, ensuring that the polarity is correct.
2.6. Instrumentation
For large installations consider the instrumentation for measurements and alarm. These include Voltmeter,
Ammeter, Ah counter, High- and low-voltage indicators, Ground fault detector(s) and
Temperature sensor(s) for the battery and the ambient air. For smaller installations use portable test equipment.
The temperature sensors shall be fixed on the cell units (side wall or negative pole).
The use of monitoring and recording systems is mandatory in “Hybrid” systems.
2.7. Commissioning charge
The initial charge is very important for the future battery operation and the battery’s service life. It is performed
as a full charge in paragraph 3.2.1. Keep the records in the battery’s logbook.
