How best to find the "best" small solar panel of a particular size?
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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.
@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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@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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You'll need to substitute a different LDO for it then.
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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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@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 :(@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.
:((((( -
@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.
:(((((@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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@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
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. -
@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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@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.
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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.
@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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@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.
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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?!
@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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@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?
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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.
