Powering mote 24/7 using only a supercap and solar
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Would it be feasible to implement mppt in software? From what I understand, the atmega328 pwm works in power-save mode (but not in power-down). Power-save mode consumes 1uA. Could the charging speed be controlled by pwm and adjusted periodically by the mcu, to keep the load on the solar cell at maximum power?
@mfalkvidd said in Powering mote 24/7 using only a supercap and solar:
Would it be feasible to implement mppt in software? From what I understand, the atmega328 pwm works in power-save mode (but not in power-down). Power-save mode consumes 1uA. Could the charging speed be controlled by pwm and adjusted periodically by the mcu, to keep the load on the solar cell at maximum power?
Like you, I've also wondered what kind of MPPT might be built by leveraging an mcu and just simple components. There is a guy on youtube ( https://youtu.be/JXSRXUiUA6M ) who built his own arduino MPPT charge controller from scratch, though for a much bigger solar panel. For me, the real quesation is: why aren't there more chips that offer a proper MPPT? It seems like a rather bizarre gap in the market.
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@gohan
Let's put it this way: there's probably nothing I could achieve with MPPT that I couldn't achieve with a sufficiently bigger solar panel. So, if space isn't a concern, the economics tend to favor buying bigger mini solar panels, because mini solar panels are fairly cheap from China (cheaper than buying the BQ25504 chip). On the other hand, for large 100watt or above solar panels, it's more economic to add MPPT, because an MPPT charge controller is cheap compared to, say, doubling an already expensive solar panel.That said, there may be other features of the chip that you may want anyway, like charge termination or a "battery_OK" pin to power-on your atmega328p when the voltage gets to an acceptible level. So, you could create those by other means, or you could buy a package with those features and which also happens to have MPPT at some incremental cost.
So, it's six of one, half a dozen of the other.
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What I finally arrived at was this:
https://www.openhardware.io/view/396/Simple-Solar-Supercap-Charger
which is both less expensive and easier to assemble. -
Anyone already doing it?
Seems like all that's needed is a supercap with low enough leakage current such that harvested solar energy exceeds leakage current per 24 hour cycle.
Yesterday I ordered a few boost converters to play around with: an AAT1217, an LTC3105, an MP3418, and an L6920DTR. Out of those four different boost converters, hopefully at least one will prove adequate. Maybe all of them will. Either way, I'm sure to learn something about what's ultimately needed.
I checked the unloaded voltage on an el cheapo solar cell (scavanged from a $1 garden light), and it came out around 1v under indoor ambient light conditions, near a window on a darkly overcast, rainy day with no indoor lights on. That's higher than what I was expecting. Of course, how much of that is ephemeral and how much of it is solid under load remains to be seen, and I guess that's part of what I'll be learning.
For illustration purposes, I put a little TH mote inside it.@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
The gardenlamp is quite handy as well, but better put some sealant on the edges of tha small solarcell as they do tend to leak. You will find everything has rusted inside after using it a season. Nevertheless, have been able to run an attiny on it
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@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
The gardenlamp is quite handy as well, but better put some sealant on the edges of tha small solarcell as they do tend to leak. You will find everything has rusted inside after using it a season. Nevertheless, have been able to run an attiny on it
The gardenlamp is quite handy as well, but better put some sealant on the edges of tha small solarcell as they do tend to leak. You will find everything has rusted inside after using it a season.
Yeah, corrosion is a huge problem with the chinese ones because it seems many of their components are incredibly prone to rusting (even including their wire!). Go figure on that one. Potting epoxy will cost you much more than the garden light. I think polyurethane spray foam may be the cheapest way to weatherproof them, and it's readily available.
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@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
The gardenlamp is quite handy as well, but better put some sealant on the edges of tha small solarcell as they do tend to leak. You will find everything has rusted inside after using it a season. Nevertheless, have been able to run an attiny on it
@Ed1500 said in Powering mote 24/7 using only a supercap and solar:
@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
Yes, for outdoors it's bright enough you don't really need a boost converter. So, your solution may be the least expensive DIY for outdoors. Interestingly, the chinese garden lights do use a boost converter. They use a special purpose IC specifically made for garden lights.
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The gardenlamp is quite handy as well, but better put some sealant on the edges of tha small solarcell as they do tend to leak. You will find everything has rusted inside after using it a season.
Yeah, corrosion is a huge problem with the chinese ones because it seems many of their components are incredibly prone to rusting (even including their wire!). Go figure on that one. Potting epoxy will cost you much more than the garden light. I think polyurethane spray foam may be the cheapest way to weatherproof them, and it's readily available.
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@Ed1500 said in Powering mote 24/7 using only a supercap and solar:
@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
Yes, for outdoors it's bright enough you don't really need a boost converter. So, your solution may be the least expensive DIY for outdoors. Interestingly, the chinese garden lights do use a boost converter. They use a special purpose IC specifically made for garden lights.
@NeverDie It was indeed more of a concept test 'can I do this with one of those lamps'. I first tried to just use the power to the LED with the nicad in place but the NiCad just won't last long coz of the continous recharge, so I took it out and put supercaps in there. Store enough charge to get through the night. Supercaps also do better in the cold than Nicads , though I admit I brought them inside when it started freezing.
But those lamps are just great little boxes for a contained attiny 13/25/45/85 project -
@NeverDie It was indeed more of a concept test 'can I do this with one of those lamps'. I first tried to just use the power to the LED with the nicad in place but the NiCad just won't last long coz of the continous recharge, so I took it out and put supercaps in there. Store enough charge to get through the night. Supercaps also do better in the cold than Nicads , though I admit I brought them inside when it started freezing.
But those lamps are just great little boxes for a contained attiny 13/25/45/85 project@Ed1500 said in Powering mote 24/7 using only a supercap and solar:
But those lamps are just great little boxes for a contained attiny 13/25/45/85 project
Exactly so. They're cheaper than most project boxes, and then you get the solar cell "for free".
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@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
The gardenlamp is quite handy as well, but better put some sealant on the edges of tha small solarcell as they do tend to leak. You will find everything has rusted inside after using it a season. Nevertheless, have been able to run an attiny on it
@Ed1500 said in Powering mote 24/7 using only a supercap and solar:
@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
Exactly which supercaps are you using, and where are you sourcing them from? It would be good to compare notes.
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@Ed1500 said in Powering mote 24/7 using only a supercap and solar:
@NeverDie actually I have done that, feeding an attiny85 and also an Atmega328 ("barebones" arduino) 2x1.5F capacitors. all on a 6 volt solar cel and a low drop regulator
Exactly which supercaps are you using, and where are you sourcing them from? It would be good to compare notes.
@NeverDie I have 5.5V 1.5F Supercaps from Aliexpress. Forgot which supplier but they do well.
I put them in an RC circuit to measure and though that might not be totally reliable, they were above 1 Farad
Ah, found them. Although. It was a year ago, the ones I have say 1.5 F but seems they now sell 1Farad
These: https://www.aliexpress.com/item/2Pcs-Ultracapacitor-1-5F-5-5V-super-capacitor-1-5Farad-farad-capacitor-5-5V1-0F/32632431698.html -
@NeverDie I have 5.5V 1.5F Supercaps from Aliexpress. Forgot which supplier but they do well.
I put them in an RC circuit to measure and though that might not be totally reliable, they were above 1 Farad
Ah, found them. Although. It was a year ago, the ones I have say 1.5 F but seems they now sell 1Farad
These: https://www.aliexpress.com/item/2Pcs-Ultracapacitor-1-5F-5-5V-super-capacitor-1-5Farad-farad-capacitor-5-5V1-0F/32632431698.html -
@Ed1500 Yep, rechecked mine. 1.5 Farad, but the 'my orders' link now points to 1 Farad caps
Thanks for looking that up. I keep coming back to this one:
https://www.digikey.com/product-detail/en/illinois-capacitor/106DCN2R7M/1572-1287-ND/5410638
if only because it seems like a good value for money, and it seems able to run any mote for quite a long time. -
Thanks for looking that up. I keep coming back to this one:
https://www.digikey.com/product-detail/en/illinois-capacitor/106DCN2R7M/1572-1287-ND/5410638
if only because it seems like a good value for money, and it seems able to run any mote for quite a long time. -
Good point. I use first class mail from digikey, which arrives in 2 days and which costs around $3.65 I think. If you order before 8pm, it ships the same day. So for me, since I usually order late in the day, it's almost like it arrives in a day and a half. :) I don't think I would order just a single supercap from Digikey, unless I was getting a bunch of them, but as I'm ordering a lot of parts from Digikey anyway, the incremental shipping cost is typically free.
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Good point. I use first class mail from digikey, which arrives in 2 days and which costs around $3.65 I think. If you order before 8pm, it ships the same day. So for me, since I usually order late in the day, it's almost like it arrives in a day and a half. :) I don't think I would order just a single supercap from Digikey, unless I was getting a bunch of them, but as I'm ordering a lot of parts from Digikey anyway, the incremental shipping cost is typically free.
@NeverDie realise though it is 2.7 Volts
sure, 3.65 is peanuts if you order a bunch.
I see they have a branch in Netherlands as well. I would pay 1.81 euro for that capacitor.. but I would pay an unbelievable 18 euro shipping? Apparently because they still ship it from the USA. Also, need to answer a bunch of question what I am going to use it for, will i resell it etc. ... So I guess DigiKey is not a viable option for me -
Don't complain about your shipping costs from Digi-Key guys. These are the rates for me, insane ! :o
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I should point out that even without a boost converter, I'm getting good charging indoors in most locations. I've been investigating boost converters just in case I want a node that's virtually bulletproof with respect to charging from low light conditions, or which needs to power 3.3v or 5v sensors. For instance, the banggood PIR sensor on the other thread requires between 2.7v and 3.3v to power it. It uses so little current though that it should be possible to power it continuously from even a solar node, so I'll be attempting that fairly soon. Obviously, doing it outdoors is nothing new and would be a piece of cake by comparison.
