How best to find the "best" small solar panel of a particular size?
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@gohan said in How best to find the "best" small solar panel of a particular size?:
it is all a matter of what components you want to use: if you go 5v you can still use a LDO to power your devices, otherwise you need a boost converter at least for arduino. As soon as I receive those buck-boost converters I'll put them to the test, but so far they are in an unknown place (tracking shows they left china a month ago and still missing any further info)
Well, yes and no. I think the challenging case is how to make it as small as possible but still low cost and fairly simple.
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Personally, with exception of a few cases, I dropped 5V boards in favour of 3.3V ones. All transmitters - nrf24l01+ or rfm69 or rfm95 or eap8266 / esp32 are using 3.3V and can be fed by 2.7V
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I think nobody is talking about using 5v boards
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I think I'm trending toward including a 3.3v boost converter with a "pass-through". So, either:
https://www.openhardware.io/view/285/33v-Boost-Converter-with-Pass-Through
or
https://www.openhardware.io/view/279/Adjustable-Boost-Converter-with-Pass-Through
or possibly:
https://www.digikey.com/product-detail/en/microchip-technology/MCP1642D-33I-MS/MCP1642D-33I-MS-ND/5137719That way, if you have a sensor that needs to be powered at 3.3v, or the voltage on the supercap has fallen below 1.8v, you turn on the boost converter, but only for as long as it's needed. All the other times, you leave it turned off and running your node directly from the supercap voltage, because boost converters are generally quite inefficient.
Thoughts?
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@gohan perhaps I misunderstood you - why do you need 5V caps?
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because if you have a 5v solar panel you can charge it directly from the solar panel and then use an LDO to get the 3.3v or a buck-boost converter to always have 3.3v (in case you are using rfm69hw that requires a little higher voltage than rfm69h). Of course you could have a 5v->2.7v buck converter to charge the supercap and then use it to directly power your boards. My only biggest concern it to avoid overcharging the supercap, so using a 5.5V supercap you have a safe margin when using a 5V solar panel (could be a 6V panel and add 1 or 2 diodes to drop voltage a little )
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@gohan I suggest looking into this if you want to avoid overcharging supercaps:
Automatic cell balancing prevents overvoltage damage to either supercapacitor while maximizing charge rate.
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I have seen theese too, it only gets more complex/expensive to make the circuit and source those special components
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@gohan Did you see this?
Click here@ceech is selling a few interesting solar harvesting boards.
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Here's the thing: when you consider the "quantity 1" price of either the chip or Ceech's boards, you could boost your voltage more cheaply by just buying a bunch of cheap solar panels and stringing them together in series. For instance, today's Digikey price for the BQ25770 is $8.12: https://www.digikey.com/product-detail/en/texas-instruments/BQ25570RGRT/296-37014-1-ND/4430487
I'm not sure how they price these chips, but it seems like they price themselves out of much of the market to the point where they become almost like novelty items.
BTW, I like what I can see in Ceech's boards, and I think they're fairly priced considering the cost of the components. I'm just trying to be objective about this.
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Likewise, I don't understand by the LTC3525D-3.3 (above) is about 4.5x the price of the MCP1642D-33 (also above), especially when the latter chip actually appears to be superior, at least on paper. Am I missing something?
[Edit: Answering my own question, it appears that the LTC3525D-3.3 has a much lower operational quiescent current. The MCP1642D-33's appears to be around 40x higher. So, that might definitely matter if you're planning to have the boost converter running all the time. ]
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I went ahead and made the switch on the node that I'm experimenting with: I'm now using a LTC3235D 3.3v passthrough boost converter. I switch it on when the node wakes up, do various measurements, then switch it off before transmitting the results if the supercap voltage is above threshold. Everything working smoothly.
I think I may next try putting a buck converter on the solar panel so I can get more juice out of it when its voltage is above 3.3v. I'll be trying this one:
https://www.openhardware.io/view/276/33v-Buck-Boost-DC-DC-Converter
because it's the only one I have on hand. If it seems to help, then I'll look for something more on-point (and less expensive!).
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UPDATE: I finally received these:
https://www.aliexpress.com/snapshot/0.html?orderId=83519564882273&productId=32644217312Even though they are smaller, under dim lighting, they showed ~4x the open circuit voltage as compared to: https://www.aliexpress.com/snapshot/0.html?orderId=83597824322273&productId=32253274314
That said, the panasonic solar panels (which are even smaller!) are about 4x their voltage (i.e. about 16x the 53mmx30mm ones) under the same dim lighting.
So, regarding the OP: yes, there are definitely quality differences that express themselves in dim lighting, and this is proof.
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@NeverDie Interesting find. Could you post the product links instead of the order links? Order links can't be visited without being logged in as the user who made the order.
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@mfalkvidd said in How best to find the "best" small solar panel of a particular size?:
@NeverDie Interesting find. Could you post the product links instead of the order links? Order links can't be visited without being logged in as the user who made the order.
I can't post a link now to the good ones, because it looks as though they are no longer being sold. I had posted links before that worked. Believe me, no one is sorrier about this than me, because I want to order more of them.
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Maybe somebody else figured too that they are good and got all of them
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I just today started using a smart diode between the solar panel and the supercap. Voltage drop across it is a mere 0.03v, so I assume that means more power is faster transfered from the panel into the supercap.
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@NeverDie said in How best to find the "best" small solar panel of a particular size?:
smart diode
what's that?
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@gohan said in How best to find the "best" small solar panel of a particular size?:
@NeverDie said in How best to find the "best" small solar panel of a particular size?:
smart diode
what's that?
It's this:
It better approximates an "ideal diode" than an actual diode does. So, it behaves like a diode, but the voltage drop is much less. I measured the reverse current leakage on it, and it's about 1ua, which is higher than some of the best diodes, but not bad.
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TI also makes a single integrated "smart diode": http://www.ti.com/product/SM74611
which I've also tried. However, it has a bigger voltage drop, so I don't like it as much. Also, TI's chip is more expensive.
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Back to the OP, here's a screen scrape of what had been the "good" small solar cells:
Here's a closeup photo of one:
It may not show so well in the photo, but what I think may be key is that it wasn't pieced together out of scrap solar cell fragments (like the "bad" one was) but rather appears to be a single piece. So, that may be a clue on what to look for in the future.
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Here's a schematic for the ideal diode that is pictured above:
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Do those solar panels handle outdoor weather?
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Not sure. There's probably a risk of UV damage to the epoxy, but that's just a guess.
At the moment, I'm focused on indoor use, which is a largely ignored category. I think outdoors is easier because, well, it's a lot brighter. For instance, novicit (above) reported "The solar panel is from China, Ebay, 110mmx70mm, 5V, 1.25W. The panel works great also. It reaches 4V in the smallest amount of light, and 5.45V (no load) in modest indirect light. In fact, it will fully recharge the supercapacitor in the morning before the sun even rises above the horizon, just from the sky brightening. (From the ~20% overnight discharged state.) It seems to charge a fully empty supercap in ~10 minutes under average light."
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If anyone has a favorite buck converter chip, or one they want to recommend, I could possibly make a PCB for it and post it on mysensors.org. Suggestions anyone?
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I received the 0.7v to 3.0v boost converter module from Aliexpress whose link I had posted earlier above. Can anyone identify the chip which is on it?
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@NeverDie it is a ME2188 from MicrOne
http://www.sz-hxdz.com/uploadfile/pdf/201605111221584282.pdf
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Anyone interested in super capacitors.
I'm working on a backup super capacitor storage board. It connects directly to the power rail and charges and balances super capacitors bank. When and if power fails the board steps in and provides power to the circuit.
It is based on LTC3110 super capacitor bi-directional charging IC.
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@ceech interesting board. Is it available that order or not yet?
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@alexsh1 Boards will be most likely available by the end of the week.
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why use supercaps on an arduino tha consumes so low current? that caps will not discharge during night,when solar panels are not producing energy.?
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They will not discharge during just one night
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@ceech
Isn't it more economic to buy just one much larger supercap, with say 16x the Farads of the supercaps in your photo? Or does a capacitor bank have some other advantages besides just higher Farads?By the way, have you found supercaps that you like which also have very low self-discharge? I've been using leakage as a proxy for self-discharge--because self-discharge data is hard to come by--but they are actually defined differently.
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@Tmaster They will slowly discharge. And depending on quality discharge times can vary a lot. The ones I'm using have a leaking current of 6uA.
Of course not always is a super capacitor a suitable replacement for a battery but where batteries are not available, suitable or safe, super capacitors can take their place. They also have some advantages - high cycle life of more than 100.000 cycles comes to mind.
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@NeverDie Not necessarily. Larger super capacitors tend to be more expensive than smaller ones. Anyway, the board on the photo is a proof of concept. I would like to see how balancing and bi-directional charging/discharging work. Besides, I have some super capacitors left from other projects.
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If you could make one the smallest as possible just for 2 supercaps, it would be a nice thing to have to integrate into an existing project to give it a little backup power.
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@gohan said in How best to find the "best" small solar panel of a particular size?:
If you could make one the smallest as possible just for 2 supercaps, it would be a nice thing to have to integrate into an existing project to give it a little backup power.
But I'm guessing you want them in series, not parallel. Am I right? I suppose that might be useful actually. Ceech's seems to be parallel, though I can't say for sure whether or not it connects two banks of parallel caps in a series configuration or a parallel configuration.
@Ceech What voltage does it supply? Are they 2.7v supercaps, or something else?
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of course I want them in series
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You know what would be interesting? A capacitor bank that accepts charge in parallel but gives it back in series after a voltage threshold has been reached. That way you could charge it with very weak voltage (e.g. from a solar panel in very weak light), and still get a useable voltage out of it without the huge efficiency losses you usually get from a boost converter running at very low currents. Of course, the ESR might be very high (since it adds) if it wasn't very low in the supercaps to begin with. Low ESR supercaps are certainly available though.
@Ceech What do you think?
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@NeverDie you mean a like battery from a hybrid car? Cells form a pack, but monitored(at least) and [possibly] charged individually. I believe that is how they are set up. It might be a way to find a reference on how to do it.
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This is the capacitors schematic:
Two caps are in series, pairs in parallel. IC only allows for up to 5.5V. But voltages can be set - charge voltage, backup voltage, trip voltage and charge current can all be set. @NeverDie There is a solder jumper pad on the board for low current efficiency selection. Some other DC-DC converters also have this option.
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Charge pumps work on this principle. It's just that they dump their higher voltage from the series configuration into another capacitor, whose voltage eventually rises to the series voltage. I guess that could work too, but you need switches which switch at very low voltages to pull it off if you're starting from a cold-start and, say, a solar panel is only providing you with extremely low voltage. I'm not sure how far below 0.6v you can find switches that still function. Same for the oscillator that typically drives a charge pump. That's why Ceech's board (that I linked earlier above) that works with a startup voltage of as low as 20mv (?) is so impressive. Or is that its lowest operating voltage, and it still requires a higher start-up voltage? I guess I should read the chip spec sheet.
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@NeverDie 20mV is stat-up voltage.
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@ceech very impressive Roman! Keep us posted when the board is ready for orders
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@ceech Is there a particular brand/source of supercaps that you recommend to fit your PCB? Or do they come pre-installed?
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@NeverDie I like those:
http://www.mouser.com/ds/2/40/AVX-SCC-1018831.pdf
Super capacitors will be installed on boards.
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I must admit, I got totally lost in the middle of this thread with so many links.
Did you manage to find a holy grail? I'm keep to change a 400mA LiPO for supercapacitors on one of my nodes
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@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
Did you manage to find a holy grail?
I haven't received the supercaps from China, so I can't comment on them as yet. I expect they should arrive by next weekend, or possibly before. However, there are lots of other supercaps that one might use.
I still think that for most people a simple 6v solar panel for around $1 on Aliexpress, together with https://www.openhardware.io/view/382/Tiny-Solar-Charger-for-27v-Mote-Supercap
and a sufficiently large supercap is all you're going to need for most things. If you have a sensor that needs 3.3v, then you will want to add a pass-through boost charger such as:
https://www.openhardware.io/view/285/33v-Boost-Converter-with-Pass-Through
or
https://www.openhardware.io/view/279/Adjustable-Boost-Converter-with-Pass-Through
that you enable when your node wakes up and disable before going back to sleep.One can get more elaborate to handle more challenging low-light cases, but for 80%+ of the cases, I would expect the above to be enough.
Fortunately, all this stuff is fairly inexpensive and easy to assemble.
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I have this Solar Powered IoT Device Kit from Cypress....but have not started using it yet. though I would post it in case you might find the BOM useful.
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@NeverDie Thanks for your suggestion. Here is a thing - I cannot find MAX8887EZK27 anywhere.
Meantime, I did manage to find this interesting article - https://www.ti5.tu-harburg.de/publications/2009/fgsn09_lifetime.pdf
And these boost converters on the e-bay:
A bit expensive, but based on a very advanced chip which may be used with supercaps.
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@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
@NeverDie Thanks for your suggestion. Here is a thing - I cannot find MAX8887EZK27 anywhere.
https://www.digikey.com/product-detail/en/maxim-integrated/MAX8887EZK27-/MAX8887EZK27--ND/6227255
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@NeverDie it is a no go for me at USD 18 delivery charge to the UK. Unfortunately, there are no other sources for this chip.
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You'll need to substitute a different LDO for it then.
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@alexsh1 in case you don't already know, octopart is great for finding sources. https://octopart.com/search?q=MAX8887EZK27
There seems to be only american sources for this component though
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@alexsh1 in case you don't already know, octopart is great for finding sources. https://octopart.com/search?q=MAX8887EZK27
There seems to be only american sources for this component thoughI did not know about this source
Well, that's the problem. The postage is golden and then if the value is greater than 20 bucks (including postage), I have to pay 20% VAT.
:(((((
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@alexsh1 @NeverDie You can substitute the MAX8887 with MIC5365.
This whole thing got me so intrigued that I'm going to make a board myself. With charger, super capacitors and DC-DC converter. I'll use MIC5365 and for DC-DC conversion TPS610986. It has loads of options. And the whole thing will cost less than 10 bucks. I've made a schematic
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@ceech said in How best to find the "best" small solar panel of a particular size?:
TPS610986
Excellent choice - TPS610986 - The TPS61098x
suits for low power systems very well, especially for the system which
spends the most of time in sleep mode and wakes up periodically to sense or transmit signals.
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@NeverDie I am sure you saw this brilliant write up by Nick Gammon:
http://www.gammon.com.au/forum/?id=12821
He experimented with 0.47F capacitor. It was enough to run a mote (<10uA in a sleep mode) overnight
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I hadn't seen it, but a mote in sleep mode draws practically nothing (<300na for combined draw from both atmega328p and RFM69). It's the self discharge rate of the capacitor more than anything which seems to govern.
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@NeverDie This is what he experienced! Have a look at the link. Within a few charges though, self discharge stabilised
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Regarding the choice of replacement LDO. If the LDO you pick turns out to have unacceptably large reverse current flow, just place the blocking diode after it instead of before it. That particular diode will leak only about 20na, and the entire issue doesn't even come up until the last ~0.3v of charging, where you'll then have a very long charge tail. However, if that were to be an issue, you could just use a larger Farad supercap, and then it wouldn't matter because you'd have enough charge already before encountering the long tail of the charge process.
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@NeverDie Thanks for heads-up. I'll keep it in mind
I found an interesting cap -
https://www.digikey.co.uk/product-detail/en/vishay-bc-components/MAL219691204E3/4705PHBK-ND/5015889Its voltage is very close to the solar panel so I think it may be connected directly via diode (0.7v drop = 6 - 0.7 = 5.3V vs 5.6V max rating)
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@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
@NeverDie Thanks for heads-up. I'll keep it in mind
I found an interesting cap -
https://www.digikey.co.uk/product-detail/en/vishay-bc-components/MAL219691204E3/4705PHBK-ND/5015889Its voltage is very close to the solar panel so I think it may be connected directly via diode (0.7v drop = 6 - 0.7 = 5.3V vs 5.6V max rating)
I've tried that cap already, and I wouldn't recommend it. It has a fairly high ESR.
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@NeverDie Given that you have been tinkering with it for a while, what caps can you recommend? With what ESR?
This cap has got 2.4 Ohm @ 1kHz - I think it is low?!
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@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
@NeverDie Given that you have been tinkering with it for a while, what caps can you recommend? With what ESR?
This cap has got 2.4 Ohm @ 1kHz - I think it is low?!
Perky explains it better than I can: https://lowpowerlab.com/forum/projects/a-solar-supercap-powered-moteino/msg18120/#msg18120
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@ceech said in How best to find the "best" small solar panel of a particular size?:
TPS610986
1.5 mm x 1.5 mm WSON Package
Not sure how easy that will be to solder?
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@NeverDie You need to get SMD rework station or oven.
This is extremely difficult to get done by even an iron with a fine tip.
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@ceech
Well, I may end up buying it from ceech then. Even properly aligning it onto the solder pads becomes difficult. I really struggled with the BQ25504. Not saying it can't be done, but just that it requires a lot more skill.
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@NeverDie and a strong magnifying glass
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Those are the boards BTW
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@ceech it is very small. Excellent. Let us know when it is ready
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And if it is too tall, still, only two capacitors can be installed in horizontal position, or even just one.
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@ceech How about a flat supercap like this:
https://www.digikey.co.uk/product-detail/en/vishay-bc-components/MAL219691252E3/4699PHBK-ND/5015883
There is no need to have two in my view unless you want to raise voltage. One flat to make the board compact may be enough.
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Flat ones are nice. Nice package. High internal resistance, therefore low current. The double cell 15F flat capacitor can only supply 70mA.
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This is great.
Maybe more people will start playing with this stuff if they can buy inexpensive pre-made boards from ceech. The more, the merrier.
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@ceech said iThe double cell 15F flat capacitor can only supply 70mA.
It should be enough if not using nrf24l01+ pa lna or rfm69HW. In this case perhaps, it would be better to have 150mA at least to cover those transmitters?
I like the size - It is really flat.
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@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
@ceech said iThe double cell 15F flat capacitor can only supply 70mA.
It should be enough if not using nrf24l01+ pa lna or rfm69HW. In this case perhaps, it would be better to have 150mA at least to cover those transmitters?
I like the size - It is really flat.If you start to get choosy, that's when it's time to start making your own boards. It's easier than you might think. Otherwise, you just have to accept that the off-the-shelf stuff will never be exactly what you want.
It's really too bad there isn't more of a universal PCB format that's easily edited, so you can simply start with a board that's close to what you want and just customize it a bit (the way one might with, say, software). For instance, even just changing LDO's--unless the new LDO has exactly the same land pattern--can necessitate redoing the board. No problem if you're the original designer, but it's a PITA if you aren't.
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I received the Chinese supercaps today. My "el cheapo" component tester is, I guess, too cheap, because it can't identify them:
So, if anyone has suggestions for a good capacitor tester, let me know.However, I did plug the first one into my solar node after charging it ,and, so far it's not holding it's charge very well at all. I'll try the green one next.
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@NeverDie I just watched this video:
Measuring the Capacitance of a SuperCapacitor – 11:54
— Julian IlettIs this what you have been looking?
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@alexsh1
I like Julien's videos, butI'd find something that's faster and more automated to be preferable, as well as something that can measure ESR too.
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Well, so far the green supercap isn't holding its charge any better. I'll leave it in-circuit for two or three days, though, and see if that improves. It's encouraging that the rate of voltage decrease is decreasing. Some supercaps apparently improve their ability to retain charge if they are forced to hold a charge long enough, though I have no idea why that is. For instance, some capacitor leakage test protocols call for holding a capacitor at its rated voltage for 72 hours before running the leakage test.
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@NeverDie you are right - Nick Gammon states exactly the same that overtime leakage "improves". A new cap has to be broken in before leakage is measured.
ESR measurement - I have no idea if it is possible to measure it and how. I think right now we are going down deep into the physics in order to do that
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For more normal capacitors (though apparently not for 10F supercaps), the little gizmo I showed in the pictures above does measure and display the ESR. That's one of the main reasons I purchased it. It's probably not hard to measure either. Measure the unloaded voltage. Then measure the voltage under, say, 1 amp of current. The second voltage measurement will be less, and from that you can calculate the ESR. At least, that's how I'm guessing it's done. Except you'd near to do a near instantaneous measurement, because the longer you drain the current, the more the voltage goes down for that reason too, not just ESR.
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Incredibly, I may have to resort to the Julien Ilett method of measuring capacitance. None of the meters or testers I've seen thus far handle supercapacitor capacitance (e.g. 10F). So, thanks for posting the video! Very timely.
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@NeverDie the old fashioned way!
Glad we are doing or reading about the same things at the same time.How long does it take for your device to measure ESR? Did you try a normal capacitor, I.e. 100uF?
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@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
How long does it take for your device to measure ESR? Did you try a normal capacitor, I.e. 100uF?
Yes. About 5 seconds.
[Edit: that includes the time it also takes to measure capacitance. It does both measurements (including part type identification) at the push of the button. ]
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Maybe it is just outside of the measurable range of the meter.
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Is there a way to do a full disconnect of the solar panel (so as to do an unloaded voltage measurement) without resorting to a relay? I've tried using a PFET, and although it can turn off the current flowing from the solar panel, it still somehow sucks the measured voltage down to about 0.3v above the supercap's voltage. On the other hand, if I physically disconnect the solar panel, then I'm able to then read it's unloaded voltaqe.
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I played around with it a bit more, and I found that if I used some external voltage source that was otherwise not part of the circuit to switch the P-FET "off", then it effectively accomplishes a full disconnect.
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Found a very good on-point thread which addresses the issue I'm having: https://forum.arduino.cc/index.php?topic=115233.0 So, it may be mosfet related, not just circuit related. If worse comes to worst, I'll order the Hexfet it references that supposedly does achieve a full disconnect the way you'd expect.
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@NeverDie said in How best to find the "best" small solar panel of a particular size?:
@alexsh1 said in How best to find the "best" small solar panel of a particular size?:
@ceech said iThe double cell 15F flat capacitor can only supply 70mA.
It should be enough if not using nrf24l01+ pa lna or rfm69HW. In this case perhaps, it would be better to have 150mA at least to cover those transmitters?
I like the size - It is really flat.If you start to get choosy, that's when it's time to start making your own boards. It's easier than you might think. Otherwise, you just have to accept that the off-the-shelf stuff will never be exactly what you want.
It's really too bad there isn't more of a universal PCB format that's easily edited, so you can simply start with a board that's close to what you want and just customize it a bit (the way one might with, say, software). For instance, even just changing LDO's--unless the new LDO has exactly the same land pattern--can necessitate redoing the board. No problem if you're the original designer, but it's a PITA if you aren't.
I do not disagree with you. I have started looking at Eagle software. Obviously, the idea is that I'm going to start with improving somebody's design first and then designing something myself
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@ceech said in How best to find the "best" small solar panel of a particular size?:
MIC5365
I'm going to switch from the MAX8887EZK27 LDO over to: http://datasheet.sii-ic.com/en/voltage_regulator/S1313_E.pdf
which also is the same size SOT-23-5 package.Why? Current consumption. The S1313 datasheet says it should consume a maximum of 1.35ua of current, whereas the MAX8887EZK27 may be consuming as much as 85ua (though I haven't actually tried measuring it). When the overall charging current from the solar panel is only around 50ua indoors far away from the windows, I'm betting it will make a difference. Likewise the MIC5365 also appears to have a rather high quiescent current of around 29ua, at least according to its datasheet that is.
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@NeverDie Solid choice.
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I did the experiment of charging one of the green Chinese cheapo capacitors for 3 days at 2.7v, and then I removed it from the circuit and measured its voltage after 3 days with no charging and no load at all. It came out at 2.54v. So, I guess I would deem that use-able.
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@NeverDie I suppose you broke it in. Try to do a few more cycles (charge / discharge) and see if self discharge improves
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It should get a little better after some cycles
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@NeverDie said in How best to find the "best" small solar panel of a particular size?:
I went ahead and made the switch on the node that I'm experimenting with: I'm now using a LTC3235D 3.3v passthrough boost converter. I switch it on when the node wakes up, do various measurements, then switch it off before transmitting the results if the supercap voltage is above threshold. Everything working smoothly.
I think I may next try putting a buck converter on the solar panel so I can get more juice out of it when its voltage is above 3.3v. I'll be trying this one:
https://www.openhardware.io/view/276/33v-Buck-Boost-DC-DC-Converter
because it's the only one I have on hand. If it seems to help, then I'll look for something more on-point (and less expensive!).How does LTC3235D compare to BQ25570?
BQ25570 has got buck converter with Vout from 3.3V down to 2V (Vbat is from 5.1 down to 2V), which is just enough to run nrf24l01+ with AVR.
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@alexsh1
Well, I'm sure it's easier to solder than the BQ25570. I'm no longer really considering anything that's difficult to solder unless there's just absolutely no alternative.It looks as though @ceech sells them though already soldered to a breakout board, so maybe he can answer your question.
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I'm playing around with a coulomb counter, actually a clone of:
https://www.sparkfun.com/products/12052The only downside to it is that it requires a minimum of 2.7v on the input current that it's measuring, which isn't really ideal for a solar panel that might nonetheless be charging at a lower voltage. It also includes its own current consumption in the measurement, and it appears to be about 75ua. In addition to counting the coulombs, you can also measure the average current between interrupts by doing a little math (which is illustrated in the sample sketche).
So, kinda cool. I changed out the sense resistor from 0.05ohm to 10ohm so that I get more frequent interrupts.
mCSTFZtUluPLYwuCR7RYaeQ
