I want to be able to charge my cell phone with a small solar cell. The charger output is 5v and 800ma. Is it possible for a small solar cell to achieve this? And if not, which is more important for charging – the voltage or the current? Any extra details would be greatly appreciated. Thanks!
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{ 3 comments… read them below or add one }
Match the voltage and if necessary wire multiple cells together in parallel to increase the current.
To quick charge your cell phone,it requires 5 volts at 800mA output. Therefore, the solar cell must able to provide 5 volts or not more than 5.5 volt. Current output can be varied any value under 800mA,but the charging time needs much longer. Example: if you have a solar cell rated 5 volts at 80mA output under full sun, and your cell phone normal fully charging time with charger is 15 minutes. By using this solar cell to charge it,requires 15mins X 10 = 150mins.
I have a 5 watt solar panel from Harbor Freight. It will charge any battery from 1.2 volts to about 16 volts. Optimum is about 12 volts, in bright sun. The maximum charging current is about 600ma, so all but the tiniest batteries can be charged safely.
In the shade the current falls to about one milliamp at about the 5 volts your battery needs. It will typically take an hour to fully charge your 800 ma battery, unless you turn the solar panel to face the sun, and out of any patches of shade. There is some possibility of destroying your battery with excessive charging. Worse the panel is about 11 inches by 16 inch by 3/4 inch, so it is not very portable. An expensive panel would be half as big or produce twice the current. Mine cost $ 39. Solar panels behave like they have an internal resistor/the value depending on how bright the sun is, about 2 ohms minimum for my panel which is why it works with any battery up to about 16 volts. It does not damage the panel to supply current to a very low impedance or even a dead short except at more than 1000 lumins, or over 100 degrees f, ambient.
The 2 square inch panels in yard lights supply a maximum of about two volts or about 100 ma, but not both unless you can give them more than 1000 lumens, so you need at least 3 of them in series to charge your 5 volt battery. 4 or 5 of them in series would likely charge your battery in less than 6 hours of average sun light. That could damage the battery, if it was mostly charged when you started. Neil