Need help in a simple Solar Cell charger!

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Khaled Elnagar

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Joined 2012
#1
Hi everyone,

First of all, I'm not specialist in the field of electricity but I love it so much. Any way, I decided to make a simple solar charger for my phone battery. All I got till now is that I should use simple cell, regulator, current limiter, charge controller and some capacitors for the regulator.

The battery needs 5V DC and 500:900 mA to be well-charged so I decided to use a simple solar cell of maybe 6-7 volts output. You know that voltage and ampere vary according to light intensity from the sun and the battery needs constant gains so I used an LM7805 voltage regulator that supplies constant +5V DC and up to 1A; this about the voltage. And concerning the current, the 1A of the regulator should be decreased to the required rate, i.e, to 500:900 mA through the current limiter.


So, I don't know how to start or how the circuit will be 😕


All I know is the regulator circuit as shown

7805datasheet-730098.gif



Thus, I need your help in how the full circuit will be
I mean " Solar cell, voltage regulator, current limiter, charger controller(that protect the battery from over-charging).... is there anything else I don't know??


Please if you know anything, don't hesitate to share me your knowledge 🙂

Regards,

Khaled
 
#2
No, you got it. You are actually powering the charger circuit in your cell phone not directly charging the battery. So the idea is to limit the voltage to 5 volts so it doesn't damage the charging circuitry.

The regulator needs 7 volts in to work properly. That means the 7805 will have to handle 2 watts of heat. Even a small heatsink will do this. If you are careful you can solder the capacitors directly to the chip. That is a basic breadboard test method.
 
#3
You are actually powering the charger circuit in your cell phone not directly charging the battery.
Click to expand...

You mean that i don't need the charge controller? its already controlled by phone circuit?


The regulator needs 7 volts in to work properly
Click to expand...

So, you think what cell should I use to achieve this keeping in mind that this cell voltage is continuously changing. I know it's a small logarithmic change but still it's a change !

That means the 7805 will have to handle 2 watts of heat.
Click to expand...

In this case, the Ampere is 1A. You think it's pretty good for the phone battery?.. You know, I got many electrical socket chargers and found their current outputs varying from 500:900 mA depending on the phone brand (Nokia, Samsung, etc).

Do I need a current limiter?


Even a small heatsink will do this
Click to expand...

Please, let me know how to provide this heatsink? you know, I'm not specialist in electronics 😀 my major is Petroleum Engineering 🙂


Thanks a lot for your reply and help

My regards
 
#5
6 or 7 volts is very borderline for the 5V regulator. I would use solar cells rated for about 9-12 volts for some safety margin. Photovoltaic cells are actually considered constant-current sources, BTW.
The charge control is built into the phone, so you only need to provide the proper voltage. An LM7805 in a TO220 package will handle this nicely. Any heat sink of a couple centimeters square should work to keep the chip cool enough.
 
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