Electronics > Projects, Designs, and Technical Stuff
Solar Powered Low Power Embedded Device
NiHaoMike:
Zener diodes tend to be "soft" in their response, while a voltage detector "snaps" on and off with a bit of hysteresis to prevent excessive cycling.
All in all, for your application, having the microcontroller adapt its power usage would be the easiest and gives the possibility of adding functionality. For example, if it's reading the sensor, it could give readings more frequently
magic:
LM385-1.2 will work as a 1.2V zener with <3µA leakage when it isn't clamping. Put a few in series for more voltage or use the 2.5V version with 10µA leakage (due to internal voltage divider).
I think it could even work to protect a NiMH cell from overcharge, while still allowing it to charge to a usable fraction of its full capacity.
Kalcifer:
--- Quote from: Kalcifer on July 02, 2020, 01:35:48 am ---
--- Quote from: Conrad Hoffman on July 01, 2020, 01:10:10 pm ---Can you get the job done with a super capacitor? How about a primary battery that you change every few years, because you'll probably be changing your rechargables that often anyway.
--- End quote ---
I've been strongly considering and looking into just using a supercapacitor. It seems to check the box for reliability and safety. It's easy to predict, and simple to deal with.
--- End quote ---
The one problem I'm seeing with this after looking into it more is that Supercapacitors appear to have a pretty large leakage current (relatively speaking).
If you look on page 10 of this datasheet, you see that for the 15F capacitor the self discharge current is around 60uA. Well my solar panel will typically only produce around 30uA-40uA, so that's a slight problem.
I need a supercapacitor on the order of 5 or so volts with a capacity >10F with a super small leakage current. Any suggestions?
EDIT: Upon further thought, I may just have to deal with a lower Capcitance. There’s a few capacitors out there with a lower leakage current, they just have a substantially lower capacitance, like 1-5F instead of 10F+.
bdunham7:
--- Quote from: Kalcifer on July 02, 2020, 07:17:21 am ---Well my solar panel will typically only produce around 30uA-40uA, so that's a slight problem.
--- End quote ---
I didn't realize that was your power limit. How do you have a solar panel that produces so little current? Even tiny LED-sized ones produce hundreds of times that amount.
Kalcifer:
--- Quote from: bdunham7 on July 02, 2020, 01:37:54 pm ---
--- Quote from: Kalcifer on July 02, 2020, 07:17:21 am ---Well my solar panel will typically only produce around 30uA-40uA, so that's a slight problem.
--- End quote ---
I didn't realize that was your power limit. How do you have a solar panel that produces so little current? Even tiny LED-sized ones produce hundreds of times that amount.
--- End quote ---
Its an amorphous silicon panel. The AM-5904. here is the datasheet.
It was my understanding that these amorphous silicon panels were optimal for low light conditions because they produce their open circuit voltage even at very low light levels, and it was just the current that changed.
If you are able to link a better panel I am all for it! I'm not attached to this specific panel at all, I just thought it was ideal for the scenario.
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