AVR-Chat

Interesting...  I read in the constant current app note that engineer for ControlTek also found the accuracy of the T15's ADC to be less than sufficient.  So he used a external voltage reference and an opamp to get the current regulation of the PWM within 10%.

I would ultimately like to have some PC communication including charge and discharge logging.

I was using the Duracell batteries with the charger.  Half maybe more start reporting errs in the charger within 10 to 20 cycles.  The ones that survive past that usually last for while although I doubt I've had any make it to one hundred cycles.  

The one that cause the errs in the 15min charger will usually take a charge in a slow c/10 charger, although I think they have reduced capacity after being slammed with so much current from the fast charger.  I would like to be able to measure their charge and discharge curves and capacities.  



--- In AVR-Chat@yahoogroups.com, David VanHorn <microbrix@...> wrote:
>
> On Sun, Mar 14, 2010 at 6:45 AM, syberraith <syberraith@...> wrote:
> > I just read Amtel's AVR-based Constant Current Supply app note, which left me wondering why would you prefer an external chip for the current regulation.  What difficulty did you have with using just one chip?
> 
> 
> 
> Codespace for one, and accuracy for another.  The T26's "precision
> reference" ended up at about 10%, I would have been better off using
> VCC as a reference.   Silicon processes that make good digital
> products generally make lousy analog.
> 
> 
> I would advise a bootloader, and a serial port.  You'll want to know
> what the chip is seeing, and why it's making the decisions that it
> does.  A terminal program can log the output for you, and help
> demystify things.  You could send temperature, current, and voltage in
> CSV format and plot in Excel.
> 
> IIRC the 15 minute chargers are only supposed to be used with their
> cells that are designed for it.  For most NIMH cells, the sweet spot
> is 1C, where the charge termination signals (rapid rise in
> temperature, voltage plateau, absolute voltage) are expressed well.
> HOWEVER: Cheap chinese cells can drive you NUTS because they don't
> have operational vents, cheaped out on the catalyst material, or got
> the electrolyte fill slightly wrong.  For your development, use only
> cells that you are absolutely sure come from a quality Japanese
> source. (Panasonic, Sanyo, etc) Definitely get the data sheets on
> those particular cells.
> 
> When you have a problem cell, you may notice that the temperature
> curve is more or less linear across the charge, without the pronounced
> spike at the end which it should have.
> You don't necessarily need a lot of precision for this, a thermistor
> on an ADC port will do, but for bonus points, look up the Hart
> Steinhart equation, and apply that to your thermistor for maximum
> accuracy. (Or implement a lookup table, after working that out in
> excel. MUCH faster!)
>