How best to find the "best" small solar panel of a particular size?
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Even with a 5V panel you still need 2 supercaps in series or get the 5v supercaps but they have less capacitance. I have ordered those 5v 4F too so I'll have to see how they behave
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Even with a 5V panel you still need 2 supercaps in series or get the 5v supercaps but they have less capacitance. I have ordered those 5v 4F too so I'll have to see how they behave
@gohan said in How best to find the "best" small solar panel of a particular size?:
Even with a 5V panel you still need 2 supercaps in series or get the 5v supercaps but they have less capacitance. I have ordered those 5v 4F too so I'll have to see how they behave
It depends on how you want to handle the charge termination. If all you want to do is use a blocking diode, as in the sparkfun schematic, then yes. However, remember that if you put two capacitors in series, they have half the capacitance. Furthermore, if you do charge them to 5v, you'll have to step down that voltage one way or another, or else you'll fry the radio on your node. That's why I've gone the direction of using a larger supercap, but terminating the charge when it gets near its rated limit. Yes, you can buy supercaps that are rated up to 5.5v, but they're relatively expensive compared to the 2.7v rated ones.
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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)
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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)
@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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@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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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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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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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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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.
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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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.
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!). -
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!).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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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.
@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.
