- Tue May 31, 2016 5:51 pm
#48353
Hi!
Thanks for your post. Cool project. I'm thinking of building somthing like that. However, I suspect that you will have a problems with the charge setup. If I understand you correctly, you limit the charge current to aboutt 250-300 mA, which is the current at max power. This will be OK when the solar panel receives full sunshine. When it doesn't, allowing 300 mA will make the voltage collapse completely and you won't charge the battery at all durine these times. The nature of solar panels is such that the voltage decreases and finally collapses as current increases. This curve changes with the intensity of the incoming light, so it's not enough to simply limit the current. Of course, you could decrease the maximum current so that the charger works also in some low light conditions. The problem is then that you won't use the time with maximum sunshine fully anymore. To get the maximum out of a solar panel you need some maximum power point tracking (MPPT). This is basically a strategy where the current is constantly adapted to result in the maximum power (voltage×current) at all times. MPPT is quite complex and expensive though. According to Adafruit, there is a good way arround this if you chose your panel properly and limit current indirectly by providing a lower voltage limit. Read about it here https://learn.adafruit.com/usb-dc-and-s ... sign-notes. The Adafruit boards are found here: https://www.adafruit.com/products/390. I hope this helps to get that charger working properly. Possibly these boards operated in constant voltage mode could be a cheaper alternative: http://www.ebay.de/itm/Single-Cell-Lith ... SwkZhWTHm-. Cheers!
Thanks for your post. Cool project. I'm thinking of building somthing like that. However, I suspect that you will have a problems with the charge setup. If I understand you correctly, you limit the charge current to aboutt 250-300 mA, which is the current at max power. This will be OK when the solar panel receives full sunshine. When it doesn't, allowing 300 mA will make the voltage collapse completely and you won't charge the battery at all durine these times. The nature of solar panels is such that the voltage decreases and finally collapses as current increases. This curve changes with the intensity of the incoming light, so it's not enough to simply limit the current. Of course, you could decrease the maximum current so that the charger works also in some low light conditions. The problem is then that you won't use the time with maximum sunshine fully anymore. To get the maximum out of a solar panel you need some maximum power point tracking (MPPT). This is basically a strategy where the current is constantly adapted to result in the maximum power (voltage×current) at all times. MPPT is quite complex and expensive though. According to Adafruit, there is a good way arround this if you chose your panel properly and limit current indirectly by providing a lower voltage limit. Read about it here https://learn.adafruit.com/usb-dc-and-s ... sign-notes. The Adafruit boards are found here: https://www.adafruit.com/products/390. I hope this helps to get that charger working properly. Possibly these boards operated in constant voltage mode could be a cheaper alternative: http://www.ebay.de/itm/Single-Cell-Lith ... SwkZhWTHm-. Cheers!
