💬 Effective Solar Supercap Boost Charger for Small Solar Panel
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@ncollins Is there a better forum than this one for discussing solar energy electronics? I've posted what I can, but it's difficult to find help/collaboration here.
@neverdie Not that I've found. A thread here, a thread there, but nothing focused. Might make sense to create a new mysensors forum category, Energy Harvesting?
Forum is a good place for conversation, but I think a wiki would really help document the results of those conversations. Also a place to provide some intro material: What is energy harvesting? Why pursue it? The easy route, the advanced route...
I'd gladly help with the content.
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I recently went looking on some of the Joule Thief forums in the hope of perhaps finding some useful circuits there. However, the problem that I repeatedly ran into was that because the inductor used by Joule Thief devotees is typically hand wound from whatever junk is laying around, it looks as though it may be difficult t to repeat their successes. It might have been easier to leverage their work if they had used standardized parts.
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@neverdie I was surprised to find the deceptive $1 solar keychain actually used a decent indoor solar cell. I can't find similar spec'd solar cell for less than $3 (at 10-20pcs). Despite the blatant false advertising, they're actually worth salvaging, especially with a solderable CR2032.
@ncollins said in 💬 Effective Solar Supercap Boost Charger for Small Solar Panel:
@neverdie I was surprised to find the deceptive $1 solar keychain actually used a decent indoor solar cell. I can't find similar spec'd solar cell for less than $3 (at 10-20pcs). Despite the blatant false advertising, they're actually worth salvaging, especially with a solderable CR2032.
How much voltage/current/power can they produce?
I've noticed that some solar cells, especially cheap ones, can leak away their current almost as fast as they can produce it.
The "fake" solar cells in your photos loosely resemble these amorphous solar cells from Panasonic: https://www.digikey.com/product-detail/en/panasonic-bsg/AM-5907CAR/869-1013-ND/2165198
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@ncollins said in 💬 Effective Solar Supercap Boost Charger for Small Solar Panel:
@neverdie I was surprised to find the deceptive $1 solar keychain actually used a decent indoor solar cell. I can't find similar spec'd solar cell for less than $3 (at 10-20pcs). Despite the blatant false advertising, they're actually worth salvaging, especially with a solderable CR2032.
How much voltage/current/power can they produce?
I've noticed that some solar cells, especially cheap ones, can leak away their current almost as fast as they can produce it.
The "fake" solar cells in your photos loosely resemble these amorphous solar cells from Panasonic: https://www.digikey.com/product-detail/en/panasonic-bsg/AM-5907CAR/869-1013-ND/2165198
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@neverdie In direct sunlight, I've seen 5.5v at around 4ma.
These seem to be the cells
SC-3222-9SC-3722-9 (edited).
http://www.vimun.cn/en/ProductInfo.asp?pid=17@ncollins said in 💬 Effective Solar Supercap Boost Charger for Small Solar Panel:
@neverdie In direct sunlight, I've seen 5.5v at around 4ma.
These seem to be the cells SC-3222-9.
http://www.vimun.cn/en/ProductInfo.asp?pid=17Come again? I don't see a cell on that list with the name of SC-3222-9.
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@ncollins said in 💬 Effective Solar Supercap Boost Charger for Small Solar Panel:
@neverdie In direct sunlight, I've seen 5.5v at around 4ma.
These seem to be the cells SC-3222-9.
http://www.vimun.cn/en/ProductInfo.asp?pid=17Come again? I don't see a cell on that list with the name of SC-3222-9.
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Which do you prefer? Those or the SC14351? For powering up the cold start electronics quickly, what I need is high voltage more than I need high current. Your solar cells are inexpensive enough that they might be a good fit for that.
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@ncollins For instance, for the price it might be a good fit for this:
https://www.openhardware.io/view/733/Buck-Energy-Harvester -
Which do you prefer? Those or the SC14351? For powering up the cold start electronics quickly, what I need is high voltage more than I need high current. Your solar cells are inexpensive enough that they might be a good fit for that.
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@neverdie I've primarily been prototyping with the SC14351 because I don't have to worry about voltage regulation when coupled with supercaps.
@ncollins Are you using the Tantalaum's primarily because they're cheap, or for some other reason?
You may be interested in this as a tiny, yet cost effective alternative: https://www.digikey.com/products/en?keywords=728-1067-1-ND
The ESR is rather high on it, but it might be good for running very low current circuits, such as logic. -
@ncollins Are you using the Tantalaum's primarily because they're cheap, or for some other reason?
You may be interested in this as a tiny, yet cost effective alternative: https://www.digikey.com/products/en?keywords=728-1067-1-ND
The ESR is rather high on it, but it might be good for running very low current circuits, such as logic.@neverdie I used tantalum because they were laying around and I was too impatient to wait for the 1206 100uf ceramic caps I had ordered.
Those are definitely interesting. The high ESR on the lower capacitance coin-cell "H-type" 0.47F super caps caused a voltage drop significant enough to trigger brownout on my first few nodes.
I was hoping to try these out, but they seem to have been discontinued https://www.mouser.com/new/Murata/murata-dmh-supercaps/.
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@neverdie I was surprised to find the deceptive $1 solar keychain actually used a decent indoor solar cell. I can't find similar spec'd solar cell for less than $3 (at 10-20pcs). Despite the blatant false advertising, they're actually worth salvaging, especially with a solderable CR2032.
@ncollins I like your idea, so I ordered some similar solar keychains from Amazon that got good reviews: https://www.amazon.com/HDE-Emergency-Flashlight-Energy-Keychain/dp/B00NFZUTR6/ref=sr_1_4?keywords=solar+keychain&qid=1572300649&s=hardware&sr=1-4
In the worst case they'll probably be no better than solar garden lights, and with the same DC boost converter ASIC, but if I'm lucky their small solar panels will put out better voltage than the 2v that's typical for garden light solar cells. Also, the packaging might be nice for a solar sensor node.
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@ncollins I like your idea, so I ordered some similar solar keychains from Amazon that got good reviews: https://www.amazon.com/HDE-Emergency-Flashlight-Energy-Keychain/dp/B00NFZUTR6/ref=sr_1_4?keywords=solar+keychain&qid=1572300649&s=hardware&sr=1-4
In the worst case they'll probably be no better than solar garden lights, and with the same DC boost converter ASIC, but if I'm lucky their small solar panels will put out better voltage than the 2v that's typical for garden light solar cells. Also, the packaging might be nice for a solar sensor node.
@neverdie Awesome. Interested to see how they work out for you.
For other options, this is the only retail outlet I've been able to find that carries different size/volt versions of the chinese amorphous panels.
https://cnmarsrock.aliexpress.com/store/group/Amorphouse-solar-panel/400691_511437499.html -
@neverdie Awesome. Interested to see how they work out for you.
For other options, this is the only retail outlet I've been able to find that carries different size/volt versions of the chinese amorphous panels.
https://cnmarsrock.aliexpress.com/store/group/Amorphouse-solar-panel/400691_511437499.html@ncollins Strange! In that case it appears that it's cheaper to buy them as part of solar keychains....
Do you happen to know: what difference, if any, is there between the solar cells that they label as "dim light indoor use" as compared to the outdoor cells?
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@ncollins Strange! In that case it appears that it's cheaper to buy them as part of solar keychains....
Do you happen to know: what difference, if any, is there between the solar cells that they label as "dim light indoor use" as compared to the outdoor cells?
@neverdie In theory, indoor is optimized for visible light spectrum. Outdoor, a combination of visible and IR. https://www.powerfilmsolar.com/about-us/the-horizon-blog/2018/08/10/outdoor-vs-indoor-solar-the-key-differences
But, who knows with these chinese panels. I haven't tested the indoor vs outdoor side by side. I do know these amorphous "outdoor" panels work significantly better indoors than the mono/polycrystalline panels I have.
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@ncollins Strange! In that case it appears that it's cheaper to buy them as part of solar keychains....
Do you happen to know: what difference, if any, is there between the solar cells that they label as "dim light indoor use" as compared to the outdoor cells?
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@neverdie Awesome. Interested to see how they work out for you.
For other options, this is the only retail outlet I've been able to find that carries different size/volt versions of the chinese amorphous panels.
https://cnmarsrock.aliexpress.com/store/group/Amorphouse-solar-panel/400691_511437499.html@ncollins said in 💬 Effective Solar Supercap Boost Charger for Small Solar Panel:
@neverdie Awesome. Interested to see how they work out for you.
I opened one up:
It appears to be the simplest possible solar charger: a solar cell with a diode and some (presumably) rechargeable batteries.
The tiny circuit board was affixed to the solar cell with sticky tape but can be pried off. Doing so reveals that the model number for the solar cell: 3722-9L,
Maybe it's this one?
http://semtronics.net/shop/index.php?rt=product/product&product_id=1123Or maybe this one?
https://www.aliexpress.com/item/32774648368.htmlTheir specs seem to mostly agree. I'm guessing that perhaps the "L" might be for "low light"?
GND on the circuit board was attached to the negative terminal on the solar cell by the faintest possible wisp of threaded wire. Removing the circuit board severed the wisp.
I found that someone else did a teardown with a similar numbered solar cell:
http://tarkus-notes.com/en/mini-chinese-solar-power-flashlight/
although his was missing the diode and it looks as though his solar panel wasn't connected. According to him, the panel would have 10.0uA at 200 lux, where 200 lux is the usual reference for indoor lighting.My own quick first test shows that I'm getting 4v open circuit under ordinary indoor LED lighting and 9uA of current when I short the leads. I would guess that it could probably power the "Effective Solar Supercap Boost Charger for Small Solar Panel" under even dimmer light, provided that the combined quiescent and leakage currents are small enough. With only a few net microamps flowing in, the margins are pretty thin.
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I went ahead and hooked up the 3722-9L to 600uF of ceramic capacitors and fed that into the "Effective Solar Supercap Boost Charger for Small Solar Panel" under indoor LED lighting, and with a red LED on the output. Sure enough, it sends out a stream of LED pulses (not very bright, but at least minimally visible if you cup your hand around the LED to shade it). I could make the pulses brighter by adding more input capacitance.
For comparison, I just now wired a brand new IXYS SM340K10l solar cell (http://ixapps.ixys.com/DataSheet/SM340K10L.pdf), which I thought would trounce the the scavanged 3722-9L under the same indoor LED lighting conditions. Granted, it is a bit smaller, but it's open circuit voltage was just 1.35v, and it's shorted current was 6uA. And it cost me $3.86 on Digikey. So, quite a surprise there. Go figure.
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I went ahead and hooked up the 3722-9L to 600uF of ceramic capacitors and fed that into the "Effective Solar Supercap Boost Charger for Small Solar Panel" under indoor LED lighting, and with a red LED on the output. Sure enough, it sends out a stream of LED pulses (not very bright, but at least minimally visible if you cup your hand around the LED to shade it). I could make the pulses brighter by adding more input capacitance.
For comparison, I just now wired a brand new IXYS SM340K10l solar cell (http://ixapps.ixys.com/DataSheet/SM340K10L.pdf), which I thought would trounce the the scavanged 3722-9L under the same indoor LED lighting conditions. Granted, it is a bit smaller, but it's open circuit voltage was just 1.35v, and it's shorted current was 6uA. And it cost me $3.86 on Digikey. So, quite a surprise there. Go figure.
@neverdie at ~$1.90 per keychain, seems like a great way to get into harvesting.
I bet it would be easy enough to design and 3d print a replacement to the button half of the housing with a little more space for a radio and sensors.
I mean, you could probably just add an LDO, HT7333 or XC6206, and use it as is.
