> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Philip Pemberton
> Sent: Tuesday, June 27, 2006 4:31 PM
> To: Microcontroller discussion list - Public.
> Subject: [EE]: Anyone got NiMH charge profile data?
> 
> 
> Hi,
>    Has anyone here got a recorded charge profile from a NiMH 
> battery? What I'm 
> after is - in effect - a spreadsheet with three columns:
>    - Time
>    - Voltage
>    - Current (optional)
> 
> Does anyone have anything like this kicking around their HDD? 
> The battery 
> manufacturers seem to be quite happy to give out pretty 
> pictures of their 
> charge profiles, but don't seem to publish actual numbers.
> 
> I want to play around with charge termination detection 
> algorithms for my 
> (half-done) NiMH charger, and I don't have any test data to 
> feed into my 
> detection algorithms. I figure while I'm waiting for the 
> parts for the 
> discharger circuitry to turn up (a DAC, a voltage reference and a few 
> op-amps), I might as well get some of the software algorithms 
> tested and 
> tweaked for use on a PIC.
> 
> What's bugging me is that the manufacturers are saying one 
> thing (wait for dV 
> to hit -5mV per cell) while all the books and websites I've 
> been scanning 
> through are saying different things. One suggested "zero 
> voltage delta" (wait 
> for dV to get close to zero) and another suggested 
> "inflection point sensing". 
> The latter involved calculating the first or second-order 
> derivative of dV/dt 
> and looking for the point where the derivative crosses zero. 
> Surely that would 
> produce the same result as zero-delta sensing though?
> 
> The main thing is that -dV is reputed to slightly overcharge 
> the cells (which 
> produces heat, which is bad) and 0dV allegedly stops that. 
> But if you get the 
> trip point wrong, you end up undercharging the cells, which 
> is also bad.
> 
> As far as preferences go, data for any cell manufacturer is 
> fine, but Sanyo 
> (or anyone who rebrands Sanyo cells - Kodak, Energizer or 
> Duracell) or another 
> name-brand (Uniross excepted) would be preferred. Same for 
> cell count - given 
> the number of cells in a pack, I can get the per-cell voltage 
> back pretty easily.
> 
> Thanks.
> -- 


Phil -

While I don't have any data on my hard drive, I can collect the data
(charge and discharge) curves using my CBA (Computerized Battery
Analyzer) from West Mountain Radio
(http://westmountainradio.com/CBA.htm).  Not terribly expensive piece of
equipment and very useful for characterizing batteries and charging
circuits.

Right now all I have handy are some 6 cell NIMH packs and a "low"
current charge design (charger pushes maximum of 750mA, battery packs
are rated at 2000mAhr) so it doesn't charge terribly quickly.

Rob 
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