Power Shield: What am I missing?

Troubleshooting
1

Hi all,

So, I have a RedBear Duo and a Particle Power Shield with its 2000 mAh battery. I have 4 9V @ 150 mA solar panels connected in a combination of series and parallel so that the combined voltage is measured to be 18V and roughly the combined current is measured to be ~300 mA when in full sunlight.

I had assumed (possibly incorrectly) that the Power Shield would effectively convert 18V x 300 mA to 3.5 V x ~1500 mA. And that 1500 mA would be more than enough to both power my Duo and charge the battery simultaneously.

But, I’m not seeing it. On the Power Shield, I get the blue light next to the 7-12V connection indicating “good power”, I get the blue light near the batter connector which is supposed to indicate charging, and my Duo continues to operate, but the battery’s SOC never rises, and in fact will decline over time.

What gives? Its as if the current remains at about 300 mA x 3.5 V (~1W, which is already about 3X the draw of my Duo), even though input wattage (>5W) is considerably higher. What is the Power Shield doing with all this energy?

Thanks in advance for any assistance.

2

Here are the schematics for the power shield
https://github.com/spark/shields/blob/master/photon-shields/PDFs/Schematics/power-shield-v210.pdf

Especially look at the power supply stage that turns your input into 5V DC.
It uses this buck converter
https://github.com/spark/shields/blob/master/photon-shields/power-shield/datasheets/RT8259.pdf

With a high supply voltage but low current draw (e.g. limited by the fuel gauge max charging current) you might see the regulator in discontinous mode
https://en.wikipedia.org/wiki/Buck_converter

3

@ScruffR thank you for your response! Looks like I have a lot to learn… fortunately, I enjoy it =)

So, I also tried placing all the panels in parallel so that I’m effectively generating 9V @ ~600 mA hoping this would raise the current level enough to avoid the potential issue of “discontinuous mode” in the regulator that you describe. Sadly, still, the Power Shield does not charge the battery, even in full sunlight.

=/