Hi there...
Im new at the forum, and i really dont know if this kind of threads are allowed in this forum.
I tought about a project that im trying to build, but my problem is i dont know a thing abut electronics (trying to learn :S), i was wondering if you guys could take a look to my project and give me something like a "guide line", so i know what kind of information should i "dig" to make this.

What i want to do, is find a way to charge my nokia battery (BL-5C), and for that i want to use solar energy.

I've reccentrly borrowed 4 solar cells from a friend, he told me that the output of those cells was "2v/500mA" each, at bright light.
Here is the picture -> solar.jpg

The transformer from nokia tells me that the

AC input is 100-240V
50-60Hz/180mA

DC Output is 5.7V/800mA

---
And now im a bit confused, i think i have to find a way to "control" the output of the cells to do not exceed the 5.7v/800mA ... right?
What exactly do i need, to do that?

I need a "name of something that lets me do it", so i can dig information about it.

Hope someone can help me in this...
Thanks
Reguards OpPoSiTe

PS- Sorry about the bad english

Current regulation won't be a problem as the solar cells won't output more curent, and a simple linear power supply should do the rest. http://www.national.com/pf/LM/LM317.html

Hello Paul
Even if all the solar cells were put in series, this would only give a max output of 8 volts. If I'm not mistaken the lm317 needs a differential voltage of at least 3V (8-5.7=2.3). Furthermore, that would only give a curent of 500mA not the required 800mA. Also, isn't the output voltage usually rated with no load, making the situation worse.
Hello Opposite

Originally Posted by Opposite

The transformer from nokia tells me that the

AC input is 100-240V
50-60Hz/180mA

DC Output is 5.7V/800mA

This is not just a transformer, I believe there is some battery charging circuitry in there as well. I believe charging a lithium ion battery is not just as simple as putting a set voltage to it, as this will lead to overcharging. If I am wrong hopefully someone will correct me.

Thanks both of you for answering, and thanks for the answers, thay sure gave me something to search for

Originally Posted by Sig239

Hello Paul
Even if all the solar cells were put in series, this would only give a max output of 8 volts.

Heres what i was thinking...
Here is the picture -> solar.jpg
(Silly draw, hope you understand it)

If i am correct, my output at bright light would be 8V/1000mA
(Am i right?)

Originally Posted by Sig239

If I'm not mistaken the lm317 needs a differential voltage of at least 3V (8-5.7=2.3). Furthermore, that would only give a curent of 500mA not the required 800mA. Also, isn't the output voltage usually rated with no load, making the situation worse..

That i dont know...

Originally Posted by Sig239

Hello Opposite

This is not just a transformer, I believe there is some battery charging circuitry in there as well. I believe charging a lithium ion battery is not just as simple as putting a set voltage to it, as this will lead to overcharging. If I am wrong hopefully someone will correct me.

Thanks, Ill see what i can find about that.
Did some "googleing" about this kind of project and found this:
http://www.fizzl.net/projects/solar_charger/
Obviously that aint lithium ion battery, the mobile is way too old, but since the transformer is the same for all nokia phone (i think), the process woulnt be so different, right?

Once again, thanks both of you
Reguards OpPoSiTe

PS- Sorry about the bad english

Hello Opposite
DO NOT follow the project in that link. That person clearly knows nothing about charging batteries, especially lithium ions.

Originally Posted by OpPoSiTe

Heres what i was thinking...
Here is the picture -> solar.jpg
(Silly draw, hope you understand it)

If i am correct, my output at bright light would be 8V/1000mA
(Am i right?)

No. You have two series strings connected to each other in parallel. If we connect the solar panels with the ratings you posted of 2V\500mA then it would give us 4V\1000mA. However, whenever you draw current from the panels there will be a voltage drop, making things significantly worse. I think we are jumping a bit far ahead though. You should read the following link carefully before moving on, so you will know exactly what the requirements are.http://www.batteryuniversity.com/partone-12.htm

It should also be noted that niether of us has a clue what additional charging circuitry is included in either the phone or the charging adapter.
Well it is 6:25AM here and way past my bedtime so I must go for now. It looks like you have enough research to keep you busy for a while anyways.

Some other battery types are a bit easier to charge. You may want to make something like this instead. I think it would be a little more versatile, and more simple to design. Just my 2 cents.

Hello Hero999
I concur. If you read that guys remarks you'll see that it doesn't even work for him. It just doesn't add up. goodnight....errr moorning

"What i want to do, is find a way to charge my nokia battery (BL-5C), and for that i want to use solar energy.

I've reccentrly borrowed 4 solar cells from a friend, he told me that the output of those cells was "2v/500mA" each, at bright light."

You need a single diode. thats it !!

but check if the cells are in series or parallel, or individual, they look individual
They should be hooked in series with a diode pointing twards the battery plus from the plus of the series cells.
I dont believe that overcharging is a problem .And the voltage need not be regulated because the battery will regulate the voltage .

Originally Posted by Nigel Goodwin

Current?, what current? - you're talking a few small solar cells, excessive current isn't likely to be much of a problem?.

exactly!
.