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Old 21st June 2012, 06:21 PM   #1
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Default 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

Click the image to open in full size.


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
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Old 21st June 2012, 08:18 PM   #2
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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.
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Old 21st June 2012, 09:39 PM   #3
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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


Thanks a lot for your reply and help

My regards
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Old 23rd June 2012, 08:12 PM   #4
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any other replies??
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Old 23rd June 2012, 09:25 PM   #5
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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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Old 24th June 2012, 01:59 AM   #6
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Originally Posted by sofaspud View Post
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.
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Old 24th June 2012, 06:46 AM   #7
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Awful... maybe. Unavoidable... most definitely.
You could use an LDO vreg like the TPS76850. Keep a mind of solar cell "in full sun" ratings.
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Old 24th June 2012, 07:47 AM   #8
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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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Old 24th June 2012, 04:07 PM   #9
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Quote:
Originally Posted by sofaspud View Post
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 View Post
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
Thanks for your link
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