SparkFun Battery Shield + Photon + Solar Cell

Hi All.

I am working on a project that involves solar power and the battery shield from spark since I can’t order the one from particle.io yet.

It is working fine! to my surprise. There are two measures I need to make my project smarter :smile:

I would like your opinion to see if I am approaching things the right way, or if you would suggest a different approach.

  1. Sunlight
  2. Are we charging the battery?

The spark fun board has an LED that turns on when the battery is being charged, but it does not provide data directly via the SDK library. I am guessing I could solder a wire directly to a PIN and detect when it sends a 1 to turn on the LED?

The sunlight I can get with ADC directly from the solar cell with a voltage divider to limit the voltage to the ADC pin. (Or if someone can recommend a better approach).

I’m not sure what you mean by that? Perhaps I don’t quite understand what you are trying to do.

The Battery Shield by SparkFun, has a red LED that lights up or indicates when the attached battery is being charged… i.e., the power consumption of the photon is lower than the power input and thus enough power remains to charge the battery. That same led turns off when the battery is being drained by usage or when the external power is not enough to charge the battery. So I plan to stick a wire to the + side of the LED and into a free input pin of the photon, so I could check when there’s power in that pin (a 1) to see if the battery is charging. I checked with a multimeter and the maximum voltage is less than 3.5vlts on the led + pin and the current is limited by the resistor for the LED. So I am guessing I am safe?

Since I am not that good yet at electronics, I am sourcing opinions of what I am about to do :smile: So that smarter brains can tell me if I am planning something stupid that will not work or fry something.

I’m in the same situation (waiting for Particle’s solar solution in Jan) and would like to try my hand at a DIY solution in the mean time. I have the Sparkfun Power Shield for the Photon now, and have a 1000mv battery connected to it, and it’s running my Photon just fine. But now I need to add a solar panel to give the battery a boost.

Would you mind posting the configuration that you’re using? I would like to know “what connects to what”. While I understand the battery hookup, I’m confused as to how to hook a solar panel into this setup.

And advise is welcome - thanks!

@Stricks
Solar panel connects to a barrel connector which you will have to solder onto the under side of the board. there is some info on their hook up guide about it. you have to be careful with the solar panel you choose too, info also in the hook up guide.

https://learn.sparkfun.com/tutorials/photon-battery-shield-hookup-guide

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Perfect - that’s just what I was looking for - thank you! I’m ordering the parts tonight, and I’ll try and remember to update this thread when I have it all up and running.

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I have this (https://www.sparkfun.com/products/13626#product-review-3521) connected to a 2.5W solar call and it’s working perfectly to charge a 1000mAh battery, running a Photon that’s sleeping for 20 min, then awakening, taking a temp/humidity reading, and going to sleep for another 20 min. After sundown it wakes every 60 min so as to conserve power. I have plenty of power at this point, even on cloudy days. I think I may have over speced it, as it seems to have more power than I need. I may have it poll more often, balancing this with the battery charge.

I tried using a 0.45W solar cell, and it just wasn’t enough to keep the battery charged. I should add this setup is running on Cape Cod (New England) in Nov, so we have relatively short days, and not a lot of sun. I do have all the data logged to a SQL database in the Cloud so I can keep accurate records of the charge/discharge.

My next test is to try and wire the LED charging light positive lead to a digital pin on the photon so I can see if the solar panel is getting enough light to charge when it polls.

What I`m going to try is a 12 volt charging solar call and use a buck convertor , to convert the 12-15v down to 5v , which should be more efficient than using voltage dividers.

I have basically the same setup with a 500mv 5v panel and no matter how much light I pound the panel with it does not charge. I checked the barrel jack and it works with an Ac adapter. What am I missing here? I read about 3.8 V at the barrel jack when it’s connected to the battery shield so I’m assuming the panel works. Perhaps my panel is no good? I have my work light right up to the panel so it’s getting tons of light.

Have you tried putting in the sunshine ?

Testing a panel is easy. Just put it in direct sunlight and hook a voltmeter up to the barrel connector. Note that the volts and milliamps you read from it will vary as to the intensity of the sun. You can also get a reading from a house lamp, but not much, and certainly not enough to charge up a battery unless you hold the panel close to the bulb.

As for charging a Lio battery, you’re implying that the panel generates enough power to charge the battery faster than your circuit can drain it. That’s why it’s best to try the panel on the voltmeter first, and connect it to your circuit later.

Visible brightness is no reliable (if at all) measure for energy “content” of light.
UV light has (virtually) no visual brightness but transmits way more energy than the brightest “white” light your work light might provide.

This is a entertaining video about the underlying physics
https://www.youtube.com/watch?v=i1TVZIBj7UA