Thanks Lee, I'd just about figured that out by looking at data sheets. :-)
> True zener diodes only exist below about 6 volts. True zeners have a large > change in their zener > voltage versus current. For example, a 1N5335 3.9v 5-watt zener will measure > about: > > 5.1v at 1200ma > 4.5v at 600ma > 3.9v at 300ma <-- rated current > 3.5v at 150ma > 3.0v at 50ma > 1.0v at 0.3ma > > In other words, it draws a *lot* of current even well below its zener > voltage. If connected right > across a lithium cell, it would soon discharge it below 1.0v, and murder it. > > In contrast, "zeners" above 6v are in fact "avalance" diodes. A different > mechanism defines their > threshold voltage, and they have a far more stable voltage versus current. > For example, a 1N5342 > 6.8v 5w zener will measure about: > > 7.15v at 700ma > 6.95v at 350ma > 6.8v at 175ma <-- rated current > 6.6v at 60ma > 4.9v at 0.01ma > > Notice that the voltage changes far less with current, and becomes > insignificant (10uA) below 5v. > > In between the two (5-6v range), the characteristics gradually transition > from one behavior to the > other. That's why you have to "test" and pick the best parts for the job. > > This means you want to use a higher-voltage "avalanche" diode across the PV > panel to limit its max > voltage; then knock this down to the desired cell voltage (and block reverse > current) with 1 or > more series diodes. > > Lee Hart > -- When something bad happens, you have three choices: You can let it > define you; let it destroy you; or you can let it strengthen you. > -- Theodor Seuss Geisel > -- > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
