Supercap Solar Powered Mysensors nodes as cheap as possible

[gohan]

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

[NeverDie]

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.

[gohan]

the booster is plugged in the Easy PCB and it is used to power arduino and sensor

[NeverDie]

@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?

[gohan]

nope, that was the 5.5v supercap version. I mean plugged in in the socket next to the green screw terminal. Of course the buck boost module now it is not used. I have to put the new photo I know.

[NeverDie]

Since you're not posting schematics, maybe it's time for a new photo....

[gohan]

I need to learn how to make schematics :sweat_smile:

[gohan]

Does it make sense? The output terminals go to the Easy Pcb green screw terminals .

[NeverDie]

@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?

[gohan]

Because only one was not dropping enough voltage to have a safe margin, the schottky is giving that extra 0.2v

[NeverDie]

You'll have a very long charge tail with the diode(s) in that position.

[gohan]

Do you mean it will take long time to fully charge?

[NeverDie]

@gohan Yes.

[gohan]

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:)

[NeverDie]

@gohan :+1:

[gohan]

Today was overcast all day so it took about 3 hours longer (until 3pm) to fully charge but overall it looks like a nice graph for the last 3 days.

[gohan]

2 days of rain and it can't charge, luckily it has more than 3 days of running time without charge. Being not in direct sunlight (vertically positioned on a wall just below roof) it has some drawbacks, but today it is catching up

[NeverDie]

The overcast days are where the two diodes are burning you.

[gohan]

if it is overcast it is not that dramatic as it still charges, it is the rainy day that is bad. I know that a more efficient and specific charging circuit would work better even at lower light/voltages, but still this is working fine as it recovered to 2.4V within 3 hours and 3 more to reach 2.5V. Unless I get 4 days or rain I should be fine but in the event of 4 rainy days I think I would be more worried about other things :D

[gohan]

That is looking great so far (the spike was a reboot after I installed the SMA antenna)