>-----Original Message-----
>From: piclist-bounces@MIT.EDU [mailto:piclist-bounces@MIT.EDU] 
>Sent: 01 August 2005 16:13
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Design Challenge - Simple SLA battery charger.
>
>
>Russell,
>
>On Tue, 02 Aug 2005 02:33:36 +1200, Russell McMahon wrote:
>
>>...<
>> LiIon tends to be dear and potentially tricky to charge (although
>> simple scheme that don't develop full capacity may be OK).
>> LiIon would be acceptable performance wise if cost was 
>acceptable wrt 
>> Lead Acid.
>> 
>> Any comments most welcome.
>
>Just one:  as far as I know there is *no* simple scheme to 
>charge Li-Ion batteries (like constant current or 
>constant voltage) - you have to follow the rules and they 
>aren't that simple! 

Actually, it can be quite simple as long as the battery is not abused by e.g. over discharging.  The cheap chinese charger that came with my RC Heli for charging the Lithium-Polymer packs is very simple indeed (though I wouldn't necessarily want to leave it unattended).  Li-Po cells are more dangerous/easily damaged than Li-Ion as well.

>Lead-Acid are by far the most 
>simple to charge and the most forgiving of abuse.
>

Not sure I agree, deep discharging kills them, and you still need a current limited constant voltage scheme.  Li-Ion essentialy requires the same scheme, but special conditions apply if the battery has ben over discharged and idealy some form of cell balancing would be beneficial (though I note that none of the laptop batteries I've pulled apart appear to have cell balancing, probably why one pair of cells always dies first).  What is really dangerous is charging to a too high terminal voltage which risks cell rupture (or "vent with flame" as the manufacturers like to call it).

NiCad's are probably the simplest overall, if ultimate life isn't a primary goal as a simple constant current, or even just a resistor can be used to charge them.

Regards

Mike

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