How best to find the "best" small solar panel of a particular size?
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Interestingly, in direct sunlight they all measure at an open circuit voltage of 7v +- 0.1v. So, go figure as to why the range is so much wider under dim conditions.
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@NeverDie were they all at the same angle to the light source? If you laid them out on a table and shone a lamp, theynwill be at different angles and have different results.
@wallyllama I would say that in the similar circumstances different solar panels do behave differently due to quality solar cells, i.e. manufacturing quality as well as efficiency.
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@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
I'm not aware of any advantages to cycling a LiPo battery. As mentioned by Gohan, though, charging to just 80% does seem to extend lifespan.
Better yet, use a LiFeP04 battery. They're safer, and you don't need to down convert their voltage because their max charge is 3.6v.
I prefer supercaps mainly because they should last practically forever.
@NeverDie said in How best to find the "best" small solar panel of a particular size?:
@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
Thanks for the pointer to Ceech. I hadn't been aware of him, but I see that his Ebay store has a lot of interesting boards, including this one:
http://www.ebay.com/itm/Solar-Energy-Harvesting-power-supply-w-LTC3108-and-super-capacitor-storage-/331974364829?hash=item4d4b36ce9d:g:tXwAAOSwmLlX4Osy
which I may order just for fun.Impossible for me to really answer your question, as it all depends on what your current drains are. A 10F supercap isn't really much compared to a 400mah Lipo.
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@NeverDie said in How best to find the "best" small solar panel of a particular size?:
@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
Thanks for the pointer to Ceech. I hadn't been aware of him, but I see that his Ebay store has a lot of interesting boards, including this one:
http://www.ebay.com/itm/Solar-Energy-Harvesting-power-supply-w-LTC3108-and-super-capacitor-storage-/331974364829?hash=item4d4b36ce9d:g:tXwAAOSwmLlX4Osy
which I may order just for fun.Impossible for me to really answer your question, as it all depends on what your current drains are. A 10F supercap isn't really much compared to a 400mah Lipo.
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That's a simple circuit, but it lacks the balancing of the supercaps or at least the individual overvoltage protection
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It's a buck converter. Here's the datasheet for the chip that's on it: http://cds.linear.com/docs/en/datasheet/35881fc.pdf
So, it's for the case of having a solar panel that produces more volts than the target device can handle. It's a larger solar panel than the ones we've been discussing.
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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 )
