The charge regulator or Battery Control Unit (BCU) shall primarily serve to protect the battery against both deep discharging and overcharging.
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.
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 production cost requirements.
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 "Two step" 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.
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 standard proposal Part 1, 2 and 3. After a visual inspection of the charge regulator, the documentation and labeling, 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/l:
• High-charge-disconnect: 2.30 V/cell
• High-charge-reconnect with 2-point regulation: 2.25 V/cell
• Low-charge-disconnect: 1.90 V/cell
• 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 load terminals (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.
Mechanical Parameters, Performance and Requirements
- Mechanical stability of all components shall be tested by vibrations test (acc. to IEC 60068-2-6, stringency, see proposed standard) and
- Shock test (acc. to IEC 60068-2-27, stringency, see proposed standard) when specimens are not packaged and not live.
- Temperature and humidity resistance shall be defined and tested in accordance with the climatic conditions of the target region (IEC 60068-1).
- For application in tropical climates, a “cyclical damp heat test” (acc. to IEC 60068-2-30) will be performed with temperatures up to 55°C (not live) and 40°C (at nominal voltage and maximum input and output current).
- Corrosion resistance and long-term stability will be evaluated after this damp heat test.
- Safety requirements shall be evaluated according to IEC 60335-1.
- Insulation resistance shall be tested according to EN 50178 or IEC 60335-1 (section 13.3) with a test voltage of 500 VDC.
- Heat development under maximum power conditions shall not exceed the limits stated in IEC 60335-1.
- Resistance to heat and fire shall be tested according to IEC 60695-2-1 (glow-wire test) and EN 60742, section 26 (ball-pressure test).
- Mechanical sturdiness of the case shall be tested according to IEC 60068-2-75 (stringency, see proposed standard) with a dead stroke hammer of 250 g from certain directions.
- The protection of the case against access to dangerous parts, penetration of foreign bodies and the entry of water (IP code) shall be tested according to IEC 60529. The minimum requirements are IP 20 for solid-built indoor applications and IP 54 for outdoor and other applications.
Comment: This draft standard proposes a protection code of IP 20, which means "no protection against water intrusion". This does not seem to provide for adequate protection in developing countries, even in solidly built houses, as the roofs of these buildings are often not as water-tight as they are expected to be in industrialised countries. The author recommends a minimum protection code of IP 32.
- The robustness of terminations and mounting devices shall be tested according to IEC 61215, test 10.14, for expansion, thrust, bending, pressure, torsion and twisting.
Abnormal Operation Precautions
- At operation without a battery, the charge regulator will limit the output voltage at the load terminals to the maximum permissible output voltage during battery operation. If relays are included in the circuit, they must stay in a stable condition.
- At operation with an extremely exhausted battery (Ubatt < 9V), a further discharge of the battery must be avoided.
- If voltage-measuring (sensor) lines are used, the stability of all thresholds must be guaranteed with open-circuited and shorted measuring lines.
- If temperature sensor lines are used, the stability of all thresholds must be guaranteed with open circuited and shorted measuring lines.
- The charge regulator must be protected against reverse polarity at the PV generator (up to maximum open circuit voltage) and the battery terminals (up to maximum battery voltage).
- Overload protection by fuses or electronic circuits shall be tested with 125% of the maximum load current.
- If the charge regulator has a separate radio outlet, its overload protection shall also be checked.
Electromagnetic Compatibility (EMC)
- Line-conducted interference emission shall be tested at least on the output (load) line in the radio-frequency range from 150 kHz to 30 MHz (acc. to EN 50081-1, limit value class B).
- Irradiated interference emission at a distance of 3 meters shall be tested in accordance with EN 55013, limit values acc. to IEC CISPR 22.
- Resistance to interference from fast, low-energy pulses (pulse group), coming from the load-side (e.g. energy-saving lamps), will be tested according to IEC 61000-4-4 (0.5 kV).
- Resistance to interference from single high-energy impulses, like atmospheric discharges (lightning), will be measured on the PV generator-to-regulator and on the load-to-regulator line according to IEC 61000-4-5 with 0.5 kV to 1 kV. Additionally, the pulse influence on the connecting lines between solar generator, battery and load should be determined.
- Optional: Resistance to interference due to electromagnetic fields shall be tested in reference to IEC 61000-4-3 (required field strength 3 V/m), only if portable or nonportable transmitters are expected to influence the operation of the charge regulator.
- Optional: Resistance to interference from electrostatic discharge measurements are only required if touching the equipment by operators or other persons is expected to influence the operation of the charge regulator (IEC 61000-4-2, stringency: 8 kV air discharge).
All test results must be documented and summarised in a test report, which can be requested from the supplier or manufacturer by the tendering institution.
The charge regulator must be clearly labelled, displaying the following information:
- Original signs (trademark, name of manufacturer or name of responsible dealer)
- Model number or type designation of the manufacturer
- Serial number
- Nominal voltage (V)
- Maximum PV generator (input) current (A)
- Maximum load (output) current (A)
- All connecting terminals must be clearly labelled with function and polarity.
- All displays must be clearly labelled with the meaning of the indication.
- Characteristic type and value of fuses must be written near the fuse holder.
The documentation delivered with the charge regulator must contain the following information and data:
- Installation instructions
- Operating instructions
- Technical data
- Troubleshooting instructions
- Safety warnings
- Information on spare parts
In particular, the documentation must indicate the following data:
- Range of operating temperature
- Range of storage temperature
- Maximum relative humidity
Physical properties of the charge regulator:
- Case dimensions
- Case properties (material)
- Degree of protection (IP Code)
- Fasteners, fixing material
- Connecting terminals, maximum cable size
- Cables (inlet, strain relief, cross-sections)
- Spare parts
Electrical properties of the charge regulator:
- Nominal voltage (V)
- Maximum PV-generator current (A)
- Maximum load current (A)
- Type of regulator (series regulator, shunt regulator)
- Working principle (PWM, two-point-regulation, state of charge algorithm)
- All used thresholds (V)
- Temperature compensation for the thresholds (mV/°C/celI)
- Service life
- Own consumption
- Overload protection
- Reverse-polarity protection
- Capability of switching to accommodate different nominal voltages
- Warning before load disconnect
- Delayed load disconnection
- Displays (LED's, display, accuracy)
- Additional functions (MPP tracking, etc.)
All data must be verified in the course of the type-test procedures. Data which are missing or do not conform to the measurements shall be conscientiously recorded.
Four charge regulators for qualification testing shall be taken at random from a production batch, in accordance with the procedure given in IEC 60410. The charge regulators shall have been manufactured from specified materials and components in accordance with the relevant drawings and process sheets and have been subjected to the manufacturer’s normal inspection, quality control and production acceptance procedures. If the charge regulators to be tested are prototypes of a new design and not from production, this fact shall be noted in the test report.
Testing / Pass Criteria
All specimens are subjected to the visual inspection, examination of the electrical parameters and a function test. Two specimens are subjected to various tests. The other two serve as replacements: Should one charge regulator fail any test, another two charge regulators shall be subjected to the whole of the relevant test sequence from the beginning. If one or both of these also fail, the design shall be deemed not to have met the qualification requirements. If, however, both charge regulators pass the test sequence, the design shall be judged to have met the qualification requirements.
As the specifications described in the above proposal version of the standard are not yet final and binding for suppliers, the following specifications were selected from various other sources.
Additionally or alternatively to the above standard-proposal, the following specifications can be selected individually to meet the local requirements in a tender for SHS and RHS:
Electrical Parameters, Performance and Requirements
The minimum rated input (PV-generator) current shall be 8 A (WB: 6 A).
The minimum rated output (load) current shall be 10 A (20 A).
The charge regulator must resist without damage the operating condition defined by: ambient temperature of 45°C, charging current 25% greater than the short-circuit current of the PV generator at Standard Test Conditions, and discharging current 25% greater than that corresponding to the full load "on" at the nominal operating voltage.
The charge regulator set points must be factory-preset with the set points applicable to the specified battery characteristics.
The voltage thresholds can only be readjusted by trained service personnel with suitable tools and measurement equipment.
Health, Optional: Two types of load will be connected: Essential and non-essential load. The regulator shall preferably have a facility to disconnect and re-connect the loads at separate settings.
Since the ambient indoor temperature is not expected to vary significantly in the specific locations where the SHS will be installed, battery temperature compensation circuitry is generally not required. The charge regulator voltage set points must be set to match the average ambient daytime indoor temperature for the battery location.
The following specification should be applied if ambient (indoor) temperatures around the battery and the charge regulator are expected to vary significantly during the year, say, by more than ±10°C. In RHS application, a temperature compensation is generally recommended.
Health, Optional: A temperature correction of -4 to -5 mV/°C/cell should be applied to the end-of-charge and reposition voltage.
Internal voltage drops between the battery and the input and output terminals of the charge regulator must be less than 4% of the nominal voltage (@ 0.5 V for 12 V in the worst operating conditions, i.e., with all of the loads "off" and the maximum current from the PV generator or when all of the loads are "on" and no current from the PV-generator is flowing.
Health, Optional: The charge regulator shall be equipped with a “voltage sensing line" by means of which the battery voltage can be measured at “zero current" and independently of the charge/discharge cable. If the regulator is positioned “electrically" close to the battery, this voltage sensing line can be omitted.
Due to charge/discharge cycling, batteries with liquid electrolyte can develop different acid-density zones in their electrolyte. This detrimental phenomenon can be avoided by keeping the electrolyte well mixed. The charge regulator will be able to raise the final charge voltage for one hour every two weeks or when the discharge voltage falls below a set value.
Optional: Controlled overcharging should be done at a constant voltage of 2.5 V/cell. Overcharging should occur after each deep-discharge and/or at 14-day intervals. Overcharging should last between 1 and 5 hours. It should be possible for controlled overcharging to be manually switched off.
Optional for valve-regulated maintenance-free batteries:
The charge regulator set points shall be factory-preset with the set points applicable to the specified maintenance-free battery characteristics. A controlled gassing or boostcharging of the valve-regulated lead-acid battery is NOT allowed, as gassing activates the release of hydrogen and oxygen through the valve, which cannot be refilled anymore.
Optional: Current compensation for the exhaustive discharge protection threshold is recommended (for larger PV systems).
Some form of state-of-charge indicator for the battery must be provided on or near the charge regulator. This device must at least indicate the battery conditions:
- suitable to operate loads (e.g. voltage greater than 12.5 VDC)
- when energy conservation is required (e.g., battery voltage less than 11.8 VDC)
- when the load is disconnected.
These indicators may be LED’s, or analogue or digital meters. The chosen device must come appropriately labelled such that the user does not have to refer to a manual to understand the current battery condition.
Optional: When the battery is within approximately 0.1V above disconnect (30 minutes before disconnect), a visual (and audible) warning must be given.
Health, Optional: The charge regulator shall display at least the following parameters:
- Terminal voltage
- Load connected/disconnected
- Regulator status (example: normal charge or equalisation)
- Charging current
- Load current
- State of charge (example: 60 %)
- Errors: Over-Temperature, Over Voltage, Under Voltage, Overload Current
Mechanical Parameters, Performance and Requirements
Fixing material (screws and wall plugs) for wall mounting shall be included.
The charge regulator shall have a strain relief for the installed cables. If no strain relief is provided inside the case of the charge regulator, an external strain relief must be delivered with the unit.
If certain inlets of the casing are not used for cables (temperature and voltage sense lines), appropriate blind caps must be installed to guarantee the IP protection specified.
The PV-generator, battery and load terminals must be able to accommodate a crosssection of 2,5 mm2 of each conductor.
Access to the terminals must be from outside (inside) the case only with suitable tools.
The charge regulator case must provide protection of at least IP32 (optional: IP43, IP54 depending on environmental conditions), according to IEC 60529.
Independently of the specified IP protection code of the case, a certain amount of protection against insects is needed for some projects. This requirement might be useful especially in tropical regions, as insects in connection with humidity can cause short circuits on print-boards and electronics. On the other hand, a protection of IP 54 (or even IP 41) will not allow any insects to enter the case.
The case of the charge regulator should be constructed to keep out insects and dust and should be corrosion-resistant. Encapsulation of the charge regulator is recommended. In tropical areas, the electronic circuit boards have to be coated with water-resistant material.
Optional: A certain amount of air ventilation of the charge regulator should be guaranteed in humid areas to avoid a condensation of water inside the case.
The ambient temperature range for operation of the charge regulator is ....°C to ....°C (normal: -10°C to +40°C, in tropical climates: +5°C to 50°C, in extremely hot desert climates (e.g. Tunisia): -10°C to 70°C).
The maximum relative humidity can be ... % (95% in tropical climates).
Abnormal Operation Precautions
The charge regulator must be protected against damage caused by short circuit of the input and output terminals, and reverse polarity of any connections.
The charge regulator must be able to resist any possible "non-battery" operating condition when the PV generator is connected and/or with any allowed loads. The charge regulator must also protect the load in any possible "non-battery" condition by limiting the output voltage to a maximum of 1.3 times the nominal value. (Full interruption of output voltage is also allowed.)
The charge regulator should allow battery charging from the PV generator for any battery voltage greater than 1.5 V/cell.
The charge regulator must resist without damage the operating condition defined by: ambient temperature of 45°C, charging current 25% greater than the short circuit current of the PV generator at Standard Test Conditions, and discharging current 25% greater than that corresponding to the full load "on" at the nominal operating voltage.
The charge regulator should be protected against induced over-voltages (caused by lightning) by means of appropriate Metal Oxide Varistors (MOVs), or Transient Voltage Suppressors (TVSs) inserted between both (+ and -) poles, at the PV-generator input and the load output.
The charge regulator must not produce radio frequency interference (AM and FM) under any operating conditions.
Optional: Some means must be provided to safely disconnect the battery and the PVmodules during servicing or repair by a technician.
The warranty period is at least 1 year. Longer warranty periods of the manufacturer will be passed on to the user.
This overview on standards for charge regulators in solar home systems is an extract of the publication: Quality Standards for Solar Home Systems and Rural Health Power Supply.