Hello,

i want to charge a 3.6v 800mAh lithium phone battery with a 4.5v 150mA solar panel. Im not to sure about how to charge lithium batteries in terms of charging current voltage etc. Is this ok to do or would i need some sort of over current/voltage protection?

Any suggestions?

Thanks.

 

hi,
I Googled: charging lithium batteries

Lots of hits, eg:
http://www.powerstream.com/li.htm

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Eric
"Good enough is Perfect"

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I didnt think it was going to be that complicated. Space is a issue as well, so im guesing a large circuit baord with temperature sensors and logic is needed. I might use say a pic to help with the requirments. Do you know of an easier way?

thanks.

 

hi,
For PIC chargers
Google: PIC lithium charger

eg:
http://www.yty.net/h/picaccu/

You must treat lithium batteries with care.

Does this link help.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

I didnt realise what was involved.thanks for your help

 

You need to be very careful charging lithium batteries. If you overcharge, short, puncture, overheat or anything like that, they can go off like bombs, sending a huge flame out all sides, deffinately not want you want (i hope )

You also have to consider heat with solar charging, since the battery may be exposed to sunlight.

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considering the work involved i need a simple circuit. Does the same ammount of care needed for nimh and nicds? for eg. If i had a 300mAh nicd or nimh battery connected to 150mAh panel and the the worst case over 8hours of pure sunlight the panel has the potential produces 1.2A (4 x over battery storage) would this damage nimh or nicds? I have seen some pretty crude circuits people have used with nicds. thanks for your time.

 

hi,
You must use a charge regulator controller to charge most battery types.

Overcharging can damage or shorten the life of a battery, with some batteries overcharging can lead to self destruction.

There are 'crude' circuits available, but do you want a long life from your expensive battery pack or an elcheapo charger.

I would recommend you spend a little more cash on a good quality charger
or a well designed solar panel charge controller...

Google for charging ni cad batteries

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Why not use a battery charger IC?
They are smart and will not overcharge a battery. Maxim-IC have many.

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I have tried to develop a charger for a lithium battery (3.6v) circuit diagram attached, its rough and not to scale. The idea is the battery is charged using PWM (from a PIC) when the solar panel is generating between 1-4volts. The output of the solar panel is fed into a voltage tripler to supply the lithium with voltages between 4v to 18v. The solar panel is also fed to a PIC which adjust the PWM to achieve an average volatge of 4v across the battery. If the voltage exceeds 4v or drops under 1v the charging ceases.

I will also use a some thermal device to send info to the PIC so when the battery pack heats up hence battery overcharging the charging stops.

Do you guys think this will work? Im not to sure sending burts of high voltage to the lithium and not too sure about the reliability of the thermal device to detect overcharging.

thasnk.

 

Sorry file to large so i compressed it.

Attached Files

Doc1.zip (4.3 KB, 7 views)

 

.

hi,
To save others having to unzip, I have made your *.doc into a gif file.

I follow the graph and explanation, OK, but what action do want us to take.

Attached Images

solar_chrg1.gif (22.3 KB, 6 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Thanks for that. I was just wondering if its ok to send large burts of volatges 18v to the lithiums batteries even nimh? and if in general would the proposal work?

 

hi,
My gut reaction would be sending 18V pulses to a Lithium battery would be a bad idea.

BUT:
I would suggest you do some web searching for this method.

If you have the voltages available in your solar panel design, why dont you use a doubler [if required] to give the battery a conventional charge.??

You plan to use a PIC/MCU to monitor the voltage and tempr anyway.?
There are a number of good designs on the web that use MCU's to do just that.

Look here:
http://www.oshonsoft.com/picchargerlcd.html

Do you follow this OK.

Regards

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Yeh thats what i thought, the site you suggested was quite helpful, i think i might just opt for a dedicated charging ic. thanks.