Standards for the Charge Regulator

This overview on standards for charge regulators is an extract of the publication: GTZ, Division 44, Environmental Management, Water, Energy, Transport: Quality Standards for Solar Home Systems and Rural Health Power Supply. Photovoltaic Systems in Developing Countries, February 2000.

The charge regulator (or Battery Control Unit, BCU) shall primarily serve to protect the battery against both deep discharging and overcharging.

Comment: To date, there is no generally accepted international or national standard available for charge regulators in PV power supply systems. As mentioned before, the most critical and delicate component in a stand-alone PV system is the battery, and given the variety of battery types and charging characteristics (and philosophies of planners), the requirements for the charge regulators also have to cover a wide range of applications.

Comment: The main requirement for a charge regulator should be that the unit itself will not become the weakest or most vulnerable component in the whole system (which unfortunately was the case in several projects in the past). From all of the experience over the last 15 years, some quite reliable equipment has been developed by various companies. The optimisation of charging characteristics and safety precautions is an ongoing development process, as highly integrated electronic components nowadays allow very complex regulation features in a minimum of space and with low productioncost requirements.

Comment see [1]: Basically, there are two kinds of charge regulators; the main difference lies in the position of the switching device. The "Series" type interrupts the connection between the solar generator and the battery, while the "Shunt" type short-circuits the solar generator. In addition, there are two main types of control strategies. In a "Twostep" control arrangement, the charging current is completely interrupted when the endof- charge voltage is reached. With a "Pulse-Width Modulation" control, on the other hand, the charging current is gradually reduced to the end-of-charge voltage level, thus keeping the voltage constant. In SHSs, both types of regulators and both control strategies serve the purpose equally well. In fact, recent systematic and independent testing experience does not suggest that there is any real advantage associated with either type of regulator or control strategy in terms of improvements to battery lifetime.

Comment: During the preparation of large-scale projects (WB Indonesia 200,000 SHSs, WB Sri Lanka 30,000 SHSs) and the worldwide PV GAP program an international standard for charge regulators is required, with specifications that can be objectively checked and tested by any qualified test laboratory. The CENELEC CLC/BTTF 86-2 committee has actually drafted a standard for charge regulators in Solar Home Systems, which was also accepted by the IEC TC 82 and is currently circulating among the committee members for discussion and correction. A copy of the current draft version (as of 07/98) was kindly made available by TÜV-Rheinland, a member of the standards committee. The final version of this standard will probably be released by the end of 2000 and will not differ much from this draft. The draft will be the basis for the following specifications:

"Scope of the Standard"
The scope of this standard comprises charge regulators for lead-acid accumulators with liquid electrolyte (vented and gas-tight). The tests described in this standard are valid for charge regulators which use the accumulator terminal voltage as the criterion for operation as well as modern control procedures (e.g. "State of Charge Algorithms"). The following standard governs the requirements placed on charge regulators permanently installed in photovoltaic systems, especially for small domestic power supplies (SHS). Here we assume that the photovoltaic generators' power classification does not exceed 1 kWp, to which the charge regulators intended for examination have been adapted."

As soon as this standard is released, the tender specification for charge regulators might be formulated as follows:

Charge regulators should have been type-tested and certified for qualification in compliance with IEC 6xxxx (number not yet available by November 1999) “Photovoltaic Systems, Charge Regulators, Part 1: Safety Test - Requirements and Procedures, Part 2: EMC - Test Requirements and Procedures and Part 3: Performance - Test Requirements and Procedures”.

The following tests must be performed and documented as described in the standardproposal Part 1, 2 and 3. After a visual inspection of the charge regulator, the documentation and labelling, the following electrical, mechanical, abnormal-operation and EMC parameters will be determined according to the described procedures.

Electrical Parameters, Performance and Requirements

• The nominal voltage of the charge regulator should be 12 V (24 V) DC.
• The charge regulator must function in accordance with one of the following working principles:
       • Voltage-controlled thresholds with:
          • Pulse-width modulation (PWM)
          • Two-point parallel (shunt) or series regulator
       • State-of-charge (SOC) algorithm with:
          • Pulse-width modulation (PWM)
          • Two-point parallel (shunt) or series regulator
• The following thresholds are required at an ambient temperature of 20°C and an acid concentration of 1.24 kg/I:
       • High-charge-disconnect: 2.30 V/ceII
       • High-charge-reconnect with 2-point regulation: 2.25 V/ceIl
       • Low-charge-disconnect: 1.90 V/ceII
       • Low-charge-reconnect: 2.10 V/cell
      At other acid concentrations, the required thresholds must be adjusted according to the manufacturer's specifications.
• A service life of at least ten (10) years of operation should be assumed.
• The charge regulator must have a clear and reliable display. lt should signal the actual operating state of the charge regulator. The display can be constructed using LEDs or an LCD display.
• The thresholds for the low-charge-disconnect must be stable (± 0.3 V) across the entire temperature range (-10°C to 55°C).
• Overcharge protection and gassing functions must be temperature-compensated for high-charge-disconnect and high-charge-reconnect thresholds in two-point regulation, whereas the hysteresis must be constant (temperature range: -10°C to 55°C). The temperature compensation must be in the range of -3 to -5 mV/K/cell.
• Own power consumption should not amount to more than 10 mA under all operating states.
• The voltage drop at the terminals of the charge regulator between battery- and loadterminals (discharging) and between PV-generator terminals and battery terminals (charging) may only amount to a maximum of 0.5 V (12 V systems) or 1 V (24 V systems) at maximum load.

• The voltage drop on the battery-lines shall be compensated by either battery sensing lines, electronic compensation or appropriate wire selection (cross-section, length). If electronic compensation is applied, the difference between battery terminal voltage and demanded thresholds of the charge regulator should not exceed 100 mV.

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