WeatherShield + supercapacitor + tiny solar cell

[HeneryH]

https://lowpowerlab.com/2017/09/15/weathershield-supercapacitor-tiny-solar-cell/

Felix,  I didn't see a way to discuss your blog post so I am posting here.

I'm confused by the voltage graph

I understand the gradual ramp down as the battery is consumed during darkness, but why such a short almost instant ramp back up to full charge?  Shouldn't the voltage either ramp up or maintain full during the daylight hours?

[Felix]

I think it might be how the sun angle hits my house siding where this glass block is. There's a peak during the morning hours. Then the sun moves above the house and that side is still brightly lit but not direct sunlight.
I can assure you this is not made up data
Notice towards the beginning there are 2 instances of the slope going down across 2-3 days. Thats when it was very cloudy/overcast and the cell just didnt provide much charging current.

[HeneryH]

I hot-gun glued the capacitor directly onto the back of the solar cell and soldered the diode and cap in-place.









The three parts I used.  Total rookie guesses on these parts, I'll post results after a full day and night of statistics are collected.


SuperCap - $6.63 ea - https://www.mouser.com/productdetail/581-scmt32c755mrba0


Solar Cell - $1.99 ea - https://www.digikey.com/product-detail/en/seeed-technology-co-ltd/313070004/1597-1417-ND/5488049


Schottky Diode - $0.41 - https://www.digikey.com/product-detail/en/on-semiconductor/1N5819/1N5819FSCT-ND/965482

[HeneryH]

My LED kitchen lights did not seem to be the right frequency to generate electricity on my solar cells but sunlight (even cloud covered) seems to charge it.

I'll paste a full 24 hr cycle tomorrow. Update - overnight and morning recharge in westerly side of the house to only indirect sunlight until afternoon.

[HeneryH]

That draw down graph above is totally not representative of normal ops.  Maybe because it was the first charge and I didn't get a full charge on it.

Actual results are more promising than I hoped.  :-)  After a full day of charge (cloudy winter day) the moteino charged to 4.91v but then drew down the supercap so slowly that I thought something was wrong with the data recording function.  The voltage just wouldn't come off of the full 4.91v.

I actually had to put the units in the dark basement for nearly a full day to force the supercap to start to discharge. I forget what time I put it into the dark room but it was about a full day and it only dropped to 4.57v.  Now that I know what to expect I can get more scientific data.

[Kilo95]

My weather station has been outside for the last 3 weeks and has never recorded a voltage below 5.01v. It stays there all the time. Super low power consumption

[HeneryH]

So one take-away here is...   don't even bother thinking about doubling up on 7.5F SuperCaps.  In fact, opposite, it would be interesting to see how low you could go before even noticing a change.

[Kilo95]

It would be interesting. It's gotten down to -9 deg Fahrenheit here once last week. Otherwise teens to 20s Fahrenheit. It'd have killed alkalines I feel pretty sure. Very impressed with Felix's supercap/solar panel idea

[Felix]

It'd have killed alkalines I feel pretty sure.

Actually I've used alkalines in the freezing cold and they worked fine. Maybe depends on their quality too.

[Kilo95]

could be maybe i had a bad batch. the supercap/solar panel definitely works well.