Incidentally, my best guess for how these things work is that they're very efficient DC-DC converters: chop the incoming power, convert it down to 14.4v (or whatever their nominal voltage is), and collect your ill-gotten gains in current. I recall doing this at the mW level while designing drivers for millimeter-wave radar at Hughes Aircraft, but this is certainly a very nice application of the principle (assuming my guess is correct.)
Reply; In general the output voltage of a solar panel that is just connected to and charging a good sized battery bank by itself without a controller will not rise above what the batteries could accept during charging (in general that is...), that is the loaded solar panel will see its output voltage dip when connected to the battery, and it would not rise to unwanted levels until the battery is fully charged. The current flow will increase as the voltage drops due to the load the battery puts on the circuit. So, the controller does not need to do anything to reduce the voltage to increase the current flow to the battery, that will happen all by itself. But it may reduce its output voltage if it 'senses' an overcharging condition, if so, then the current flow will also drop. But there is an important gain to be had here that has not been discussed, that is that by using these controllers when the voltage of the (loaded) solar panel would fall below what could charge the battery, the controller can boost the voltage to a level that will result in the battery being charged, so that even though there is some loss through the controllers, the gains made by being able to store this power that is otherwise unavailable can far outweigh these losses and add a significant amount of stored power that would otherwise be unavailable. What happens with such a switch modes output when the load is disconnected from the controller (say with this application) is that the output voltage will simply go to a pre-programed level, provided there is any input of course. With a normal dc-dc design, there will be a tiny load always on the output so that in a quiescence state the voltage does not rise above what it is supposed to be. The current flow at that point is negligible. If you were then to look at the voltage of a solar panel connected to such a design you would see that its voltage is quite high, 18-20VDC, almost as it would be if the solar panel was simply dis-connected. As far as impedance matching functions, switch mode circuits (of which a dc-dc converter is one) do this automatically as part of their function. A similar circuit,the "D" class audio amp, also has impedance matching due to its nature, you don't need to know the ohms value of speakers connected to its output (within limits of course). Such a circuit is inherently more efficient than older designs, since they only use power when it is needed and don't waste most of the input power as older designs did. (again within limits). -Ken _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [email protected] To unsubscribe send an email to [email protected] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
