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Yet Another Solar Question
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Yet Another Solar Question

by xorlando on Thu Dec 17, 2020 10:50 am

I was happy to finally hook up my PiZeroW to solar w Lipo using this rig:https://www.adafruit.com/product/390

I have the solar feeding it, and a Lipo charging off it.

To power the Pi, I made a frankencable by snipping a USB and splicing the leads to the JST cable.
To my surprise, this worked! I had the Pi running for hours, not plugged in to DC; I stayed shelled in over wls to run a sensor script.
In hindsight, I think it was drawing off the battery.

Since then, the Pi will flicker at best, but not come online. This includes after the Lipo is done charging.

I had thought that the Pi would draw power directly off the solar, until there wasn't enough voltage, at which point it would fail over to the battery. Now I'm not sure what's meant to happen.

All I know is it did work for a brief (relative moment). My goal of a wireless solar-powered weather station is a little closer.

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Re: Yet Another Solar Question

by adafruit_support_bill on Thu Dec 17, 2020 11:06 am

The Load outputs of the charger will switch from the panel to the battery when the sun goes down. But do note that the voltage at the Load outputs is not constant. When the panel is providing power, the output will be the panel voltage (around 6v in good sun). When drawing from the battery, the output will be at the battery voltage (3.2V-4.2V depending on the charge state of the battery).

Ideally, the Pi would like to see a constant 5v supply. You can achieve that by inserting a buck/boost converter between the solar Load outputs and your Pi: https://www.adafruit.com/product/2190

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Re: Yet Another Solar Question

by freefuel on Sun May 09, 2021 10:54 pm

will the 2190 Buck/Boost converter tolerate a 3 cell LiPo battery?

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Re: Yet Another Solar Question

by adafruit_support_mike on Sun May 09, 2021 11:59 pm

Do you mean a 3P battery with three cells in parallel (output voltage 3.3V to 4.2V) or a 3S battery with three cells in series (9.9V to 12.6V)?

A 3P battery shouldn't be any problem. A 3S battery could exceed the Verter's 12V input limit.

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Re: Yet Another Solar Question

by freefuel on Mon May 10, 2021 3:48 pm

yes a 3S pack, 12.6 Volts is likely, on the data sheet for the inverter chip it states the absolute maximum input voltage is 17 volts.

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Re: Yet Another Solar Question

by adafruit_support_mike on Mon May 10, 2021 10:41 pm

Absolute max is the "don't complain to us about anything that happens afterward" level.

The table of typical operating conditions marks the boundaries of where the device has to meet the rest of the published specs. Outside those limits, performance is 'unspecified'.

Datasheets trade on failing to mention inconvenient details, and TI's writers are experts at evasion. The rest of the datasheet pointedly fails to mention voltages higher than 12V.. banner specs on the front page, performance graphs, anything.. which I see as a strong hint that performance drops off without doing any permanent damage.

You're welcome to give it a try, but I can't make any promises about performance.

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Please be positive and constructive with your questions and comments.