On Fri, 24 Jan 2003, Peter Mcalpine wrote:

*>ok, with an MPPT system, I am not 100% confident I understand
*>what I need to measure with my uP..
*>I can disconnect load from the cell - and measure open solar
*>voltage level.. I also know at that time what my battery is
*>with no charge.
*>
*>So, I then connect my SMPS and ramp it through and see where
*>a maximum current output is?
*>(given that I have enough solar voltage at the time etc)
*>
*>Is that the basic concept or have I missed the point?

Yes, that would be the idea imho. You turn on the SMPSU and try to output
your desired charge current. If at this time the input voltage sags below
the required voltage at the smps input, back off smpsu duty cycle until
the output current reaches a maximum and thenceforth 'hunt' around this
peak by changing the duty cycle a little and seeing what happens to the
output current. I.e. increase 3% duty -> if current increases -> keep this
new value, else keep old. Decrease 3% -> if current increases -> keep this
new value. A PIC can do this very well (you need two AD inputs for this,
the third probably to check battery voltage and steer the charger logic).

*>also, if it is a SMPS circuit and I went for an IC for that
*>solution, I suppose I could use an DA output from my uP to
*>the feedback port on the SMPS IC instead of a PWM control..
*>
*>P.S. what is the recommended 'fast' charge for NiMh generally?

1C or 1.5C depending on manufacturer. Some say 2C is ok. 1C is probably
conservative. But life is shortened by fast charging afaik.

Peter

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