Olin Lathrop wrote: > > Testing the open circuit panel volts only takes a few > > mS, you can then do the PWM for a few seconds so power > > lost in the test is almost nothing. Remember it charges > > the large input cap during the open circuit voltage > > test so much of that energy is not lost anyway if you > > keep the test time short enough, ie once that cap voltage > > rises and stabilises the test is done. > > I think you *don't* want the cap there. It will slow down the rise > to open circuit voltage and hold the panel at inefficient voltages > for too long. Yes, the energy produced by the panel during the test > is captured, but overall energy production is diminished. > > Instead, I would completely open circuit the panel (no cap) for very > short periods occasionally. Even if it taks a whole millisecond every > second, only .1% of the available power is lost. Actually it should > be able to stabalize in much less time than that, so there would be > no power loss in a practical sense. I've only been skimming this thread up til now, so I'm not sure where this concept of measuring the open-circuit voltage of the panel crept into the discussion. The V-I curve of a panel is far from linear, or even constant, so the open-circuit voltage has very little to do with the maximum-power point. You need to measure the actual output voltage and current of the panel simultaneously in order to calculate and maximize the power. It may make more sense to measure actual voltage and current into the load, as this is really the power you want to maximize. This would then take into account any variations in the efficiency of the regulator. Although you will want to vary the operating point occasionally to see whether the optimum value has changed, the zero-current point is not the most useful place to look. -- Dave Tweed -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.