Supercap Solar Powered Mysensors nodes as cheap as possible
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Yes, he used those pcbs from aliexpress that do overvoltage protection, but those are sized for much bigger caps and wouldn't fit much into small boxes. For what I could understand the sab mosfets work while the supercap discharges to keep voltage even across them, so you have to be careful not to apply a higher voltage than the maximum combined of the caps in series. If I could find a way to make a overvoltage protection with some simple components I'd be fine with it.
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Not long ago someone (was it you?) posted a link to a youtube video where some guy had a charge balancing circuit that wasted very little power, IIRC. He's probably selling it now. Maybe you could just buy one of those?
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I maybe up to something: I used a MCP1700 ldo and on Vout a diode + a schottky in series to drop the voltage ( could have used just the diode, but the Vout was 2.7x volts so for supercap longevity I added the schottky to have a safe margin) and it is charging even with panel pointed away from the sun. I'll see how it goes tomorrow, but I am pretty happy with the results so far. If it works I think i can't go cheaper then a LDO + 2 diodes :v:
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What is the cost? Also, it's not clear to me how much usable charge you're getting.
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1.5€ for solar panel, 1.7€ for 100F supercap, 1€ for booster and some cents for MCP1700, diodes and a small PCB. A fully charged supercap gives 3 days of working time, with send every 10 minutes of temp. hum, TX rssi, RX RSSI, battery voltage and battery percentage
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Sounds sorta roughly like the kind of circuit used in solar garden lamps, except you've replaced the typical rechargeable battery with a supercap and are boosting to a higher voltage than they typically do. I wonder whether any of them do boost to the same voltage that you're targeting? Perhaps the brighter ones, for example? Those solar garden lights typically have a single, inexpensive integrated circuit that does it all.
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@gohan said in Supercap Solar Powered Mysensors nodes as cheap as possible:
the booster is plugged in the Easy PCB and it is used to power arduino and sensor
By "plugged in," do you mean like in your earlier photo?
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Since you're not posting schematics, maybe it's time for a new photo....
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@gohan said in Supercap Solar Powered Mysensors nodes as cheap as possible:
Does it make sense?
I suppose. Why the two diodes again instead of just the one?
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You'll have a very long charge tail with the diode(s) in that position.
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It took about 5 hours to charge and it wasn't in direct sunlight, I'm still happy with the results given I'm using general purpose parts I already had around and no sophisticated charge controllers (and no particular knowledge about electronics :sweat_smile:)
