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Selected Problems in Designing of a Charge Controller for 6V PV Installations
W. Grzesiak, J. Poczatek, T. Pisarkiewicz, M. Jaskiewicz
Stand-Alone PV System, Solar Charge Controller, MOSFET
Components for PV Systems
Subtopic: Balance of System Components
Event: 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
Session: 4BV.1.13
3652 - 3655
ISBN: 3-936338-25-6
Paper DOI: 10.4229/24thEUPVSEC2009-4BV.1.13
0,00 EUR
Document(s): paper


The challenge in designing a solar charge controller is to maximize the efficiency of the energy transfer from the module to the battery. There are many sophisticated and expensive microprocessor-based controllers on the market, which offer advanced matching techniques. However, due to simplicity, reliability and competitive price, analogue shunt- and series-type controllers are still preferred for some installations. Design of such a controller for a 6V photovoltaic system raises some problems, which do not exist e.g. in 12V or 24V installations. That’s why such solutions, indisputably wanted, are rather completely not available on the market. An analogue controller usually requires a blocking diode, which prevents the battery from being discharged by the module. The voltage drop across commonly used Schottky diodes is typically about 600mV and more. Thus, in a 6V system such diode would dissipate at least 10% of the power from the PV module. An innovative approach replaces the diode with a MOSFET showing very little on-resistance, which can reduce the voltage drop to less than 100mV for typical currents. Specialized circuitry is added to sense the source-drain voltage and drive the MOSFET to act like an almost ideal diode. This solution significantly increases both efficiency and reliability of the controller. Designing a charge controller for 6V PV systems also requires careful choice of op-amp supply voltage and MOSFETs, which will operate at lower gate-source voltages than in controllers destined for higher-voltage systems. Attractive employment of much more convenient conventional semiconductors needs introducing complicated charge-pumps. Special requirements must deal with the controller’s configuration, length and cross-section of conducting paths due to voltage drops, so significant in the low 6V circuitry.