Solar + Electron Charging Circuit


#1

I have had success powering Electrons with 6v 2 watt solar panels. Mostly given decent lighting conditions, the Electrons stay up and have absolutely no problem. I am curious about adding some sort of solar optimization to the devices I have out in the field. The problem that I have with most of the charge controllers out there i.e Sparkfun Sunny Buddy, Adafruit DC Solar Charger is that they take away the ability to read the battery level from the Electron. Has anyone come across a solar charge controller that increases the efficiency of a solar panel while also maintaining the functionality of the PMIC?


#2

I know I cannot answer your question but I am glad you are having some success with the solar panels. I plan to have a similar setup eventually.

Which brand of solar panels are you using? And would you be kind enough elaborate on the lighting conditions (indoor/outdoor or dim/cloudy)?

Thanks in advance!


#3

I have around 150 devices working on solar power. They all are working on a 6v 2 watt solar panel from Voltaic systems.

All the solar panels are mounted to the side off dumpsters. The dumpsters are in various locations around a heavily forested area. I had to estimate whether or not they would work at a particular location or not. If the panel’s got full sun for maybe an hour or two that would be enough to recharge the electron for that days usage ~3-4%. It really depends on how much power your Electron uses during the day. Something else to consider is the movement of the sun as the seasons change. I have a few locations that work well in the summer but in the winter as the angle of the sun changes, those locations no longer work. There’s also the alternate case where an obstruction causes the summer time light to be reduced. Unfortunately I just had to test each location and switch over to a long term battery where necessary.

Thus far serious weather conditions haven’t caused too many problems with Electrons staying charged. I have seen charging happen on overcast foggy days. The deciding factor is usually if theres no obstructions to the little light that gets through on overcast days.


#4

The PMIC on the Electron can be tweaked to limit the solar panel from operating too far below their Vmp (The voltage where they cell provides the maximum current).

I set the PMIC voltage limit above 5v to keep the panel from operating below that voltage where they would start operating out of their peak current voltage band. It’s a crude form of MPPT tracking, and it works very well with the 6v solar panels.

Just search the form for Electron Solar Code, and you should come up with the code I have shared to do this along with the code that puts the Electron to Sleep once it hits a preset battery SOC level like 20%. Then it waits for the solar to recharge above 20% before starting back to normal operation.