How best to find the "best" small solar panel of a particular size?
-
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.
-
@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 :(I 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.
:(((((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.
-
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.
@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)
-
@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)
@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.
-
@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.
-
@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?!
@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
-
@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
@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?
-
@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?
-
@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. -
-
@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. -
And if it is too tall, still, only two capacitors can be installed in horizontal position, or even just one.
@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.
-
This is great. :+1: Maybe more people will start playing with this stuff if they can buy inexpensive pre-made boards from ceech. The more, the merrier. :)
-
Flat ones are nice. Nice package. High internal resistance, therefore low current. The double cell 15F flat capacitor can only supply 70mA.
@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. -
@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.@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 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.
