💬 Effective Solar Supercap Boost Charger for Small Solar Panel
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@neverdie said in 💬 Effective Solar Supercap Boost Charger for Small Solar Panel:
TPS61200
Looking at the example Single Solar Cell usecase http://www.ti.com/lit/an/slva345b/slva345b.pdf, it seems the expectation is minimum input 3ma at 0.5v? Maybe for startup, but lower current requirements after?
As for the small solar cells in series, I have thought about that too, but occasionally I have sensors that get hit with direct sunlight. I've fried a couple of NRF24 modules that way. I like the idea of using a 5v amorphous solar panel charging a 5.5v supercap + an LDO (with a passthrough?).
I want a harvesting module that boosts and dumps voltage into a very small supercap 2.7v with enough capacity for one boot/wakeup + sensor read + transmission. Once the small supercap is charged, the input voltage boosts up to 5v and is redirected into a larger storage supercap. , the the small super cap should be charged by the storage supercap when charge input is too low to be boosted. If necessary, the storage supercap could be boosted to charge the small supercap.
Basically, do whatever it takes to get ready for the next transmission, then store in a reserve. If under voltage, boost it, if over voltage route through LDO, else passthrough.
@ncollins I think the booster designs are good fun for seeing just how far one can push the limits. So, with that in mind, I decided to do an exploratory breakout board for the most extreme booster out there , namely the LTC3108:
https://www.openhardware.io/view/732/Extreme-Energy-Harvester
For solar cell applications in dim light it may need to be managed though, because otherwise it may (?) collapse the input voltage and simply stall. i.e. it needs to be pulsed. If I'm lucky, maybe with a large enough input capacitor it will pulse itself. If not, it will need some kind of external control to manage it. Unfortunately, datasheets rarely provide that kind of insight, so in most cases one simply has to build and test in order to know for sure.Maybe a trigger circuit simiar to this would work, but it woud need to work at a very low voltage level, and therein lay the rub:
Maybe one of these jfet oscillator circuits would work at an appropriately low voltage:
http://www.dicks-website.eu/fetosc/enindex.htmThe trick would be getting it to work not only at a very low supply voltage, but a very low supply current as well.
If anyone has ideas or suggestions, please post.
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@neverdie according to a few datasheets 2v at 200lux. The solar cells delivered were HENGYANG SC-3514.
http://www.vimun.cn/en/ProductInfo.asp?pid=18
http://www.solars-china.com/solars/indoor-solar-cells.pdfOn my windowsill, 2.5v typical in-direct sunlight, 2.7v is the highest I've recorded in direct sunlight.
So far, most of my Aliexpress buys have been fine for my needs. Haven't really gotten close to making a "production ready" module, so for prototyping it's been fine.
One exception: I thought I had a genius idea to repurpose these $1 solar powered keychain flashlights. They had an amorphous solar panel, rechargeable battery, button, leds and a housing...for $1. I bought 20 of them. First one I opened up, I realized it's a lie!
The solar panel is just glued to the circuit. The battery is just a normal non-rechargeable CR2016.
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@ncollins I've noticed that a number of the dollar store "solar calculators" are fake as well. They give the appearance of being solar powered, but in reality they run on a small battery instead.
@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.
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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.
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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?
