# Newbie needs help!

Discussion in 'Alternative Energy' started by OpPoSiTe, Jul 28, 2006.

1. ### OpPoSiTeNew Member

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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

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3. ### Sig239Member

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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
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.

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5. ### OpPoSiTeNew Member

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

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?)

That i dont know...

Thanks, Ill see what i can find about that.
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

6. ### Hero999Banned

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Those diodes are connected backwards so it'll discharge the batteries into the solar pannels possibly damaging them. I personally wouldn't charge Li ion batteries with a simple circuit like this, however I've heard that they'll be fine providing the current is very low.

7. ### Sig239Member

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

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.

8. ### Sig239Member

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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

9. ### audioguruWell-Known MemberMost Helpful Member

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A lithium battery is a hazzard if it isn't charged correctly.
You don't want to be near the extremely hot white flame from an overcharged lithium battery burning.

10. ### williBNew Member

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"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 .

11. ### audioguruWell-Known MemberMost Helpful Member

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What limits the current? The fire?

12. ### Nigel GoodwinSuper ModeratorMost Helpful Member

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

13. ### audioguruWell-Known MemberMost Helpful Member

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I though his solar cells are 500mA.
The battery is a dinky little thing for a cell phone. It won't take much over-charging current to set off the chemical reaction:
Overcharging causes rapid oxidation which produces heat, which causes even quicker oxidation which produces more heat, which ruptures the case and lets oxegen in to make it really hot!

Here is what Analog Devices says about lithium battery charging:

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exactly!
.

15. ### john1Active Member

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Hi,

I do not believe that overcharging or undercharging by as little as 1%
would be a problem.
I think they are mistaken or lying.

John

16. ### audioguruWell-Known MemberMost Helpful Member

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All semiconductor makers have Li-Ion battery charger ICs with very good accuracy. Linear Technology has one with 0.35% accuracy. They don't want the battery to burn.

Green Batteries have a FAQ about Li-Ion batteries:

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17. ### bryan1Well-Known Member

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Well I pulled apart a brandnew laptop battery I got to use the lithium ion batteries for my electronic projects. These batteries are rated at 4.5 volts and 4 amp hours so I've put 3 of them in series to get a 13.5 volt battery pack. All I do to charge them is stick them on my nife batterybank which at night usually sits around 13.5 to 14 volts. I've left that battery pack on the nife batteries for nearly a week after I forgot to take them off and when I did take them off they weren't hot and were sitting on 13.8 volts . I know this isn't the ideal way to charge a lithuim battery but 12 months down the track that little battery pack is still going strong.
Note I only do this as I know the top voltage my nife batteries can do is 15 volt due to the shunt regulator circuit I made diverts the excess voltage to a dumpload.

18. ### OpPoSiTeNew Member

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Ok, now im getting confused :S

19. ### audioguruWell-Known MemberMost Helpful Member

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I just looked into a Sanyo cell phone's Li-Ion battery. It is rated for 3.6V. Inside it has two cells a little bigger than an AA size in parallel measuring 3.755V (it hasn't been charged for about 6 years) and a very small circuit board packed with ICs and things. I don't know the power adapter's voltage for this phone and I don't know if the electronic circuit inside the battery is its charger.

20. ### StopGoNew Member

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Really risky idea...

The nokia battery (BL-5C) is a bare bones Li-ion, it has no protective supervisory circuit, if you fail to charge it right then you risk exploding batteries and the *very* nasty stuff inside them getting out.

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