LowPowerLab Forum
Hardware support => Projects => Topic started by: HeneryH on October 10, 2017, 04:55:51 PM
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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 (https://lowpowerlab.com/wp-content/uploads/2017/09/WShield_SolarCell_Voltage.png)
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?
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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 :D
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.
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I hot-gun glued the capacitor directly onto the back of the solar cell and soldered the diode and cap in-place.
(https://i.imgur.com/jEPxuOg.jpg)
(https://i.imgur.com/bZ4q3bz.jpg)
(https://i.imgur.com/XyHDBio.jpg)
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.
(https://www.mouser.com/images/avx/images/SCM_SPL.jpg)
SuperCap - $6.63 ea - https://www.mouser.com/productdetail/581-scmt32c755mrba0
(https://media.digikey.com/Photos/Seeed%20Technology%20Ltd/MFG_313070004.jpg)
Solar Cell - $1.99 ea - https://www.digikey.com/product-detail/en/seeed-technology-co-ltd/313070004/1597-1417-ND/5488049
(https://media.digikey.com/photos/Fairchild%20Semi%20Photos/261-DO-41.jpg)
Schottky Diode - $0.41 - https://www.digikey.com/product-detail/en/on-semiconductor/1N5819/1N5819FSCT-ND/965482
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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.
(https://i.imgur.com/7G03v1g.png)
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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.
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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
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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.
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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
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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.
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could be maybe i had a bad batch. the supercap/solar panel definitely works well.