EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: mdijkens on October 01, 2020, 12:25:56 pm
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I have built a small sensor project based on an ESP8266 that runs +7 months from a single 1000mAh lipo.
How can I charge this lipo with a tiny solarpanel in ambient (indoor) light? I assume an average of 1 mW is already enough to keep it charged. (e.g. 3mW during the day, 0mW during the night)
I was thinking of the same small solarpanels you see/saw in watches/calculators/clocks etc. Max a few cm^2
Is it possible?
What kind of solarpanel / charging circuit could I use to keep it efficient?
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Those small panels seen in cheap solar powered gadgets usually charge a nom. 1.2V NiMH battery. You'd need several in series or a boost converter designed for energy harvesting to get them to charge a LiPO.
Perhaps look at panels with more cells in series for a higher output voltage?
Googling: energy harvesting solar to LiPO (https://www.google.com/search?q=energy+harvesting+solar+to+LiPO)
returns some useful results, including articles from Hackaday and various chip manufacturers.
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Thanks for the link. I'll start reading into that
First article surprises me a bit, since it looks exactly like what I'm trying to achieve, but he's talking about direct sunlight.
In direct sunlight I even get to 100+mA with a regular TP4056 and a 3x5cm solarpanel. This however won't charge anything without direct sunlight, so not suited for indoor use...
I think I also need specific solarcells for ambient light?
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You'd need a high efficiency amorphous solar cell. e.g see https://panasonic.co.jp/ls/psam/en/products/pdf/Catalog_Amorton_ENG.pdf
However in 200 Lux illumination (bright office) you'll have great difficulty finding anything smallish capable of delivering even 0.1mA, an order of magnitude less than you need.