A question occurred to me, and that is with very low currents in uA's, does the electrolytic capacitor's current leakage while charged divert much needed current away from the CPU at low light levels?
I recently bought a Classwiz fx-991EX (I liked it so much, I'm purchasing more of them). I've done some basic experiments on the Solar cell power characteristics (removed the 991EX's 22uF electrolytic buffer before starting), in which unsurprisingly I found a large amount of light is needed to do difficult and long calculations purely on Solar energy (~600+ lux, which is about the light from being near a window on a sunny day). Interestingly though, the fx-991EX seems to have some type of power management control built in, so while the display disappears completely when the lux is lower than about 300 (with an indoor 9W LED, it seems to do better with natural light), both the history and variable storage seems to be retained down to about 5-6 lux (~3.5 metres from a 9W LED lamp at night), so while not usable at lower light levels, memory is retained at much lower levels than any other solar cell scientific I have (usually once I lose the display due to insufficient light, quite often the memory contents go, but this is not the case with the fx-991EX).
It makes sense to me for a purely solar powered calculator like the Casio fx-260II Solar to have that buffer, or dual powered calculators that retain the history contents on power off (eg Sharp EL-W516X), or programmable calculators (eg Casio fx-3650P), to give a bit of time to replace the battery. But since the fx-991EX doesn't really keep it's history (well that isn't strictly true, statistics, vectors, matrices and equation variables in equation mode are retained on power off), it isn't clear how necessary it is.
I have an older fx-3600PV and fx-50F, both of which don't have electrolytic capacitor buffers, but are functional even down to about 27lux or so (though the fx-3600PV isn't really readable at this level of light). Still it is interesting that these 2 programmable models from the late 1980's didn't bother with a capacitor buffer.
One unintended advantage to removing the electrolytic capacitor on the fx-991EX, is that the solar power indicator seems much more accurate and responsive. For example ~600+ lux (No battery, just on solar power) it can perform a long calculation, but the display does fade (and calculation time slows); With a battery installed and under the same light conditions I get a slow flickering on/off solar power indicator during calculation, so that seems to fit with what I see under solar power only. Before with the electrolytic capacitor, the solar power indicator would be solidly lit even under 27 lux which is completely insufficient to power the display, and only enough to maintain the memory contents, while now under similar light conditions the solar power indicator is almost always off.
Anyone know whether electrolytic capacitor leakage current could draw a significant portion of the miniscule current supplied by solar cells at low light levels, or in other words, does removing the electrolytic capacitor buffer allow a solar powered calculator to work under even lower light levels than it would with the capacitor?
I'm not an electronics person (I just know some basics, though I must admit even some of those basics I know could be wrong), so if what I bought up isn't right for a number of reasons, it would much appreciate an explanation to correct my misunderstandings!
I love solar powered scientific calculators, which is why this post is so long, obsessive and wordy
Edited by MJim, 03 December 2020 - 07:15 AM.