I have some charge data, will e-mail later tonight.

Steve

----- Original Message ----- 
From: "Philip Pemberton" <philpem@dsl.pipex.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Tuesday, June 27, 2006 2:30 PM
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.                         | Kitsune: Acorn RiscPC SA202 64M+6G 
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