Jim, some of what I said is from observing the voltages of the controllers.. you may have to go find the original patents (probably expired now) to get all the detail and then that may even be somewhat out of date. If you find something interesting, please post it.. as I said.. I am speculating on some of this. I have not tried googling this (which is usually a good idea first).
Regarding watching the voltages, if you have an MPPT controller, you can often see the search algorithm working with a DVM. The only way the controller can find the maximum power point voltage is to actually "visit" that voltage and measure the power. So the MPPT controller will do a voltage sweep by varying the impedance the panel sees. The sweep voltage range may be fairly small (.5 volts or ?? - the controller that did the sweep every 90 seconds varied the voltage by about 5 volts) and if the actual max power point voltage is outside the sweep range, the next sweep will start at or near the higher power end point and the controller quickly heads to and finds the actual voltage maximum power point. Even if the sweep is too fast for the DVM, you can still see the voltage dithering around the max power point.
Since the thread has drifted.. another interesting thing I saw recently measuring my Victron MPPT controller with a 160 watt solar panel. Pretty much all of these MPPT controllers require that the solar panel voltage be higher than the battery voltage before the controller will operate. This likely keeps the switcher topology a little simpler but it might seem that you are losing out on some of the solar power available by not trying to convert the power at say 8 volts (way below the battery voltage).
But.. my 160 watt solar panel was reaching 12 volts with a load of only 4 ma. By the time the controller turned on at around 16 volts, the current the panel was producing was still under 10 ma. That is a tiny amount of power.. on the order of 1/10 watt and less than one thousandth of what the panel is capable of. Switching converters need some power to just operate and would consume all of that just turning on.
So... these MPPT controllers dont turn on until a the solar voltage is somewhat above the battery voltage - because there just isnt any power below that voltage worth converting.
Regarding watching the voltages, if you have an MPPT controller, you can often see the search algorithm working with a DVM. The only way the controller can find the maximum power point voltage is to actually "visit" that voltage and measure the power. So the MPPT controller will do a voltage sweep by varying the impedance the panel sees. The sweep voltage range may be fairly small (.5 volts or ?? - the controller that did the sweep every 90 seconds varied the voltage by about 5 volts) and if the actual max power point voltage is outside the sweep range, the next sweep will start at or near the higher power end point and the controller quickly heads to and finds the actual voltage maximum power point. Even if the sweep is too fast for the DVM, you can still see the voltage dithering around the max power point.
Since the thread has drifted.. another interesting thing I saw recently measuring my Victron MPPT controller with a 160 watt solar panel. Pretty much all of these MPPT controllers require that the solar panel voltage be higher than the battery voltage before the controller will operate. This likely keeps the switcher topology a little simpler but it might seem that you are losing out on some of the solar power available by not trying to convert the power at say 8 volts (way below the battery voltage).
But.. my 160 watt solar panel was reaching 12 volts with a load of only 4 ma. By the time the controller turned on at around 16 volts, the current the panel was producing was still under 10 ma. That is a tiny amount of power.. on the order of 1/10 watt and less than one thousandth of what the panel is capable of. Switching converters need some power to just operate and would consume all of that just turning on.
So... these MPPT controllers dont turn on until a the solar voltage is somewhat above the battery voltage - because there just isnt any power below that voltage worth converting.
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