I agree. I needed a 2.5v zener reference voltage (half way on a 5v system). It took a 3.9v zener to get the 2.5v I needed when biasing it with something like a 10k resistor... Bob
-----Original Message----- From: EV <[email protected]> On Behalf Of Lee Hart via EV Sent: Tuesday, June 2, 2020 4:10 PM To: Electric Vehicle Discussion List <[email protected]> Cc: Lee Hart <[email protected]> Subject: Re: [EVDL] Question about charging small LiIon batteries Peter VanDerWal via EV wrote: > Wouldn't it be better to have a 3.9V zener across the battery? > Unless thay have leakage current when off? > > If I'm going to put it across the panel then I'd probably want a 4.3V > zener, and then drop ~0.4V between the panel and the battery? > > The result doesn't have to be precisely 3.9V on the battery, just > somewhere in that neighborhood. (Warning: Technical discussion to follow. May cause drowsiness...) 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)
