Need help in a simple Solar Cell charger!
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 21st June 2012, 06:21 PM #1 Khaled Elnagar   diyAudio Member   Join Date: Jun 2012 Location: Egypt Need help in a simple Solar Cell charger! 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 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
 21st June 2012, 08:18 PM #2 simon7000   diyAudio Member   Join Date: Nov 2008 Location: Oakmont PA 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.
Khaled Elnagar
diyAudio Member

Join Date: Jun 2012
Location: Egypt
Quote:
 You are actually powering the charger circuit in your cell phone not directly charging the battery.
You mean that i don't need the charge controller? its already controlled by phone circuit?

Quote:
 The regulator needs 7 volts in to work properly
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 !

Quote:
 That means the 7805 will have to handle 2 watts of heat.
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?

Quote:
 Even a small heatsink will do this
Please, let me know how to provide this heatsink? you know, I'm not specialist in electronics my major is Petroleum Engineering

My regards

 23rd June 2012, 08:12 PM #4 Khaled Elnagar   diyAudio Member   Join Date: Jun 2012 Location: Egypt any other replies??
 23rd June 2012, 09:25 PM #5 sofaspud   diyAudio Member     Join Date: Nov 2005 Location: San Antonio 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. __________________ It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
Khaled Elnagar
diyAudio Member

Join Date: Jun 2012
Location: Egypt
Quote:
 Originally Posted by sofaspud 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.
The problem is any drop-out in voltage will appear as heat, this is in fact awful thing. But anyway, I'll find the suitable cell to use.

 24th June 2012, 06:46 AM #7 sofaspud   diyAudio Member     Join Date: Nov 2005 Location: San Antonio Awful... maybe. Unavoidable... most definitely. You could use an LDO vreg like the TPS76850. Keep a mind of solar cell "in full sun" ratings. __________________ It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
 24th June 2012, 07:47 AM #8 tauro0221   diyAudio Member   Join Date: Nov 2008 Location: Victoria,TX Hi, Here it is a link to Linear Technology read top page 19. It look like this is what are you looking. Link to Linear Technology:http://cds.linear.com/docs/Datasheet/3108fb.pdf
Khaled Elnagar
diyAudio Member

Join Date: Jun 2012
Location: Egypt
Quote:
 Originally Posted by sofaspud Awful... maybe. Unavoidable... most definitely. You could use an LDO vreg like the TPS76850. Keep a mind of solar cell "in full sun" ratings.
I think this type is great, I'll try to change mind

Quote:
 Originally Posted by tauro0221 Hi, Here it is a link to Linear Technology read top page 19. It look like this is what are you looking. Link to Linear Technology:http://cds.linear.com/docs/Datasheet/3108fb.pdf

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