# Charging/Powering from SOLAR CELLS

i'm eying this one Solar cell panel having specification's as follows:

Typical Peak Power 0.55Watt Voltage at peak power 5.5 V Current at peak power 100mA Length 70mm, Width 55mm

i wanted to charge a 5volt battery(connecting 3 cells of 1.5volt each so making it 4.5v) or using two of these panels to charge a 9volt rechargeable battery and then power Arduino and a RF Module(both can work easily at 5volts ,although in arduino have to plug in 5volt pin's so as to bypass the Voltage Regulator ).

What you people Suggest?, or Any better idea's or correction's you would like to make?

Common People!

Lots of things change in the ouput of a solar panel in the course of a day, particularly a small one. I would investigate a solution using a DC-DC converter that accepts a wide range of input voltage, maybe 7 to 20, and convert it to the regulated five volts you need. At such low power and voltage any diodes or active elements will block current and consume a lot of the power. Use a shunt regulator, perhaps a zener to determine the highest voltage the battery will have across the terminals and shunt the surplus to ground after the battery is charged.

I would have to chase down the right part, but they are for sale.

Or, in lieu of the shunt regulator, watch the battery voltage with the arduino and shunt the power supply to ground through a transistor and resistor when it is fully charged. A pwm output could keep it just right.

Pay attention about the capacity of your battery. The current producted by the panel must not be bigger than the capacity divided by 10. For example if your power cell is 40A/h it cannot accept values bigger than 4A maximum as input. With yours numbers the cell capacity must be > 1Ah

cantore: Pay attention about the capacity of your battery. The current producted by the panel must not be bigger than the capacity divided by 10. For example if your power cell is 40A/h it cannot accept values bigger than 4A maximum as input. With yours numbers the cell capacity must be > 1Ah

Well that's an over simplification - a good rule of thumb for lead-acid batteries. Some kinds of battery do not tolerate over-charging at all (LiPo for instance). Others are fairly tolerant (NiMH for instance which just generate heat when overcharged). The best solution is to have a regulator circuit between solar cell and battery which should perform two functions: prevent over-charging of the battery and prevent over-discharge (under-voltage).

Using a DC-DC converter is not a good idea as solar cells are not constant-voltage sources - pull too much current and they drop steeply to zero volts, pull too little current and you waste most of the sunlight. Circuits to do a good job use 'peak power tracking'.

Also what batteries are you proposing that are both rechargeable and 1.5V ?