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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-24 9:39 |
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Conference: Bucharest University Faculty of Physics 2011 Meeting
Section: Biophysics; Medical Physics
Title:
Charging of Ni-MH batteries with solar PV cells
Authors:
Marian Mocanu
Affiliation:
1)“Politehnica” University of Bucharest, Faculty of Electronics, Telecommunications and Information Technology
2)Faculty of Chemistry, University of Bucharest
E-mail
cuantic63ma@yahoo.com
Keywords:
Solar cells, rechargeable batteries, switching regulator, Buck converter;
Abstract:
Solar panels are often used in combination with batteries to provide energy for portable electronic systems and another applications [1,2,3,4,5,6,7]
The ambition of this project is to charge these batteries with solar energy. The energy harvested
from the solar panel should be efficiently relinquished to the rechargeable batteries.
The ratio of solar panel no-load voltage to battery voltage determines the choice of converter.
Circuit Description. A step up converter also called as Boost converter is used if the solar panel no load voltage is lower than the voltage of the discharged battery, while a step down converter (Buck converter) is used if the ratio of the panel voltage under load is higher than that of the fully charged battery.
The solution was to implement a switching regulator, which can have an efficiency approaching 90 percent. The National Semiconductor LM 2574 [8] (with max. output current 0.5 A) is a simple switching regulator that requires a minimum number of external components.
The operating principle of the switching regulator is that energy is stored in the magnetic flux of the inductor and switched into the load. Since flux and not charge, as in the charge pump converter, is used to store energy, the voltage may be higher, lower, or the inverse of the input voltage.
A step-down (buck mode) regulator converts a high voltage to a low voltage. The output voltage is compared to an internal voltage reference.
The experimental photovoltaic panel have 12-18 photoelements (Silicium thin films technology). The I-V characteristic measurements was performed for all photovoltaics cells.
I used ten rechargeable NiMh (Nickel-Metal hydride) AA 600 mAh 1.2V The charging voltage is in the range of 1.4–1.6 V/cell. A fully charged cell measures 1.35–1.4 V (unloaded), and supplies a nominal average 1.2 V/cell during discharge, down to about 1.0–1.1 V/cell.
With this system, the energy provided by the solar cells is enough to operate a standalone AM-FM receiver without any external power source. For more power I used a step-down switching regulator based on integrated circuit LM 2596 with max. current 3A and 5V output voltage.
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