💬 Effective Solar Supercap Boost Charger for Small Solar Panel
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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.
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@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.
@ncollins I'm curious as to why you aren't using your 3722-9L's on your solar motes?
Is it because you're more geared to collecting sunshine instead of nighttime indoor lighting?Curiously enough, during the daytime (but still indoors) I found the IXYS is pumping twice the microamps as the 3722-9L So, clearly, the two boards respond to different spectra differently. The IXYS gives its "external quantum efficiency" for different wavelengths. In contrast, I haven't seen any reference to wavelength efficiency by the 3722-9L, but apparently I got lucky and it's optimized for the kind of light the LED's in my office are emitting. Regardless, the 3722-9L always has more open circuit voltage than the IXYS cell I referenced earlier.
By the way, as an aside, I put a 10,000 uF capacitor on the "Effective Solar Supercap Boost Charger for Small Solar Panel," and now it blinks the red LED plenty bright enough to see without having shade it.
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@ncollins I'm curious as to why you aren't using your 3722-9L's on your solar motes?
Is it because you're more geared to collecting sunshine instead of nighttime indoor lighting?Curiously enough, during the daytime (but still indoors) I found the IXYS is pumping twice the microamps as the 3722-9L So, clearly, the two boards respond to different spectra differently. The IXYS gives its "external quantum efficiency" for different wavelengths. In contrast, I haven't seen any reference to wavelength efficiency by the 3722-9L, but apparently I got lucky and it's optimized for the kind of light the LED's in my office are emitting. Regardless, the 3722-9L always has more open circuit voltage than the IXYS cell I referenced earlier.
By the way, as an aside, I put a 10,000 uF capacitor on the "Effective Solar Supercap Boost Charger for Small Solar Panel," and now it blinks the red LED plenty bright enough to see without having shade it.
@neverdie It's mostly because I haven't figured out how to appropriately, efficiently handle the wide voltage range of the 3722s.
In ambient light, they'd be perfect, but most locations in my house, there's a chance they'd get hit with direct sunlight. In a couple of my earlier prototypes, I fried the NRF module after the supercap exceeded 3.6v (damaged something that causes them to draw ~1-2ma).
In my case, I don't have a lot of artificial lighting, but I do decent direct/indirect sun from windows for at least part of the day.
Thoughts:
- add a really efficient LDO between the 3722 and the super cap
- Sacrifice size compact size and jump up to 5.5v supercaps. Add LDO between the supercap and mote
- rig some kind of a pass through when vout < 3.6, else go through LDO
I'm mostly avoiding the issue by using the SC-3517s. A single cell wasn't really cutting it unless in direct sunlight, so I double up in parallel.
Bonus: other prototypes
Uses your boost charger
Testing out 50mF low ESR super cap
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@neverdie It's mostly because I haven't figured out how to appropriately, efficiently handle the wide voltage range of the 3722s.
In ambient light, they'd be perfect, but most locations in my house, there's a chance they'd get hit with direct sunlight. In a couple of my earlier prototypes, I fried the NRF module after the supercap exceeded 3.6v (damaged something that causes them to draw ~1-2ma).
In my case, I don't have a lot of artificial lighting, but I do decent direct/indirect sun from windows for at least part of the day.
Thoughts:
- add a really efficient LDO between the 3722 and the super cap
- Sacrifice size compact size and jump up to 5.5v supercaps. Add LDO between the supercap and mote
- rig some kind of a pass through when vout < 3.6, else go through LDO
I'm mostly avoiding the issue by using the SC-3517s. A single cell wasn't really cutting it unless in direct sunlight, so I double up in parallel.
Bonus: other prototypes
Uses your boost charger
Testing out 50mF low ESR super cap
@ncollins That AVX-BestCap looks like a great find. I love the compact form factor of it. Looking at the datasheet though, I worry that the self-discharge of 5-10ua might be a bit much: http://catalogs.avx.com/BestCap.pdf
That's high enough that it might consume either all or at least much of the microamps produced by the 3722-9L (assuming just a single cell is used) when there's light available, and the leakage would continue overnight in the darkness to eat into whatever had been accumulated.On the other hand, the all aluminum caps at that same 50mF capacity are huge and for that reason not such a good fit either for a sensor that aspires to be compact.....
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@ncollins That AVX-BestCap looks like a great find. I love the compact form factor of it. Looking at the datasheet though, I worry that the self-discharge of 5-10ua might be a bit much: http://catalogs.avx.com/BestCap.pdf
That's high enough that it might consume either all or at least much of the microamps produced by the 3722-9L (assuming just a single cell is used) when there's light available, and the leakage would continue overnight in the darkness to eat into whatever had been accumulated.On the other hand, the all aluminum caps at that same 50mF capacity are huge and for that reason not such a good fit either for a sensor that aspires to be compact.....
@neverdie With all of your energy harvesting approaches, how are you handling unforeseen restarts? Almost all of my harvesting sensors have the same issue: if they drop below 1.8v (depending on BOD) they can't recover without manual intervention. Only one of my nodes has ever recovered and I think it's because the solar panel produced enough current to push through the MCU and radio startup.
My thought was to use the MIC2778 supervisor ic (datasheet), which has programable hysteresis, and a mosfet to wait for supercap/battery to reach a voltage high enough to handle a cold start.
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@neverdie With all of your energy harvesting approaches, how are you handling unforeseen restarts? Almost all of my harvesting sensors have the same issue: if they drop below 1.8v (depending on BOD) they can't recover without manual intervention. Only one of my nodes has ever recovered and I think it's because the solar panel produced enough current to push through the MCU and radio startup.
My thought was to use the MIC2778 supervisor ic (datasheet), which has programable hysteresis, and a mosfet to wait for supercap/battery to reach a voltage high enough to handle a cold start.
@ncollins Yes, that should work. Since I disabled BOD in order to sleep at very low currents (100na for the atmega328p), I built my own in hardware using a voltage detector. So, if voltage drops below 1.8v, it cuts off the power. When it goes above the hysteresis point, it restarts.
If you leave BOD enabled, I think it may do this work for you, and then you wouldn't need more hardware. But then your sleep current would be higher. So, it's a tradeoff as to how you want to do it.
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@ncollins Yes, that should work. Since I disabled BOD in order to sleep at very low currents (100na for the atmega328p), I built my own in hardware using a voltage detector. So, if voltage drops below 1.8v, it cuts off the power. When it goes above the hysteresis point, it restarts.
If you leave BOD enabled, I think it may do this work for you, and then you wouldn't need more hardware. But then your sleep current would be higher. So, it's a tradeoff as to how you want to do it.
@neverdie yeah, the fixed hysteresis of the internal BOD (328p, NRF51) isn't wide enough to handle startup for my nodes. I'm guessing it's due to the high ESR and corresponding voltage drop of the supercaps I've been favoring.
I also didn't realize how chatty mysensors can be during start up. My latest nodes have MY_PASSIVE_NODE enabled, skip presentation, and use dumb sleep.
