Supercap Solar Powered Mysensors nodes as cheap as possible

[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)

[NeverDie]

Since your goal was "as cheap as possible," what was your final tally on how much it cost? It would be good to know just how cheap is possible.

[gohan]

@gohan said in Supercap Solar Powered Mysensors nodes as cheap as possible:

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

I already wrote it 3 weeks ago. :D

[NeverDie]

So, something like $4 then I guess at today's exchange rate.

@gohan said in Supercap Solar Powered Mysensors nodes as cheap as possible:

.5€ for solar panel, 1.7€ for 100F supercap, 1€ for booster and some cents for MCP1700, diodes and a small PCB.

[gohan]

yes 5$ range, of course you need to add the other costs like box, the node itself and everything you need to have the node working outdoor

[NeverDie]

I wonder if you might do better with the cheaper 10F chinese supercaps. Obviously they hold less initially, but the question boils down to whether they end up holding more in the end if only because they're losing charge at a much slower rate. I don't know what the answer will be. It's really an empirical question.

[gohan]

Of course a better quality one would hold the charge better, but at what cost? Would it be really beneficial also from a cost perspective? Maybe, I don't know... It could be that a couple of good quality 10F caps are fine and that you could get away also with a smaller/cheaper solar panel, it's all a matter of trying 😀