Sounds like plenty of maths to implement just for one
feature.

John


--- Michael Rigby-Jones
<Michael.Rigby-Jones@bookham.com> wrote:

> 
> 
> >-----Original Message-----
> >From: piclist-bounces@mit.edu
> [mailto:piclist-bounces@mit.edu] 
> >On Behalf Of Rolf
> >Sent: 16 January 2007 15:46
> >To: Microcontroller discussion list - Public.
> >Subject: [EE] Li-ion charging questions
> >
> >
> >
> >I have 3 questions...
> >1. Is there some way I can calculate a "degree of
> 'chargedness'".  I 
> >want to get an idea of how close the cell is to
> being fully 
> >charged, and 
> >preferably  to indicate something like "35minutes
> charging 
> >still required". 2. Is there a way to calculate the
> capacity 
> >of the cell during (or even 
> >at the end of) the charge process? It would be nice
> to say 
> >"The cell has 
> >been charged to 1800mAh capacity". 
> 
> If you want to do this yourself, then beware that
> it's a complex problem. The basic strategy is to
> integrate the current  going into or out of the
> cell.  The nominal value of the integrator gives an
> idea of the current state of charge of the battery,
> BUT the rate of integration has to be modified
> according to cell temperature and current (e.g. cell
> capacity drops as current demand increases).  The
> integrator also has to be reset when the cell is
> fully discharged, and the maximum value of the
> integrator has to be stored when the cell is fully
> charged, to take into account the aging of the cell.
> 
> The good news is that there are several ready made
> IC's that will do all this for you, Google for
> "li-ion gas gauge" or "li-ion fuel gauge".  Every
> Li-Ion laptop battery will have one of these devices
> in it, accessed via an SMB or System Management Bus,
> which is essentialy an I2C bus.
> 
> Microchip used to have some devices for Li-Ion
> "smart" batteries but unfortunately a quick search
> shows that they are no longer recommended for new
> designs.
>
http://ww1.microchip.com/downloads/en/DeviceDoc/21904b.pdf
> 
>
http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=412&uiTemplateId=NODE_STRY_PGE_T
> http://para.maxim-ic.com/cache/en/results/4669.html
> 
> Hope that helps
> 
> Regards
> 
> Mike
> 
> 
>
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