Solar mintyboost calculations

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kevinrs
 
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Solar mintyboost calculations

Post by kevinrs »

Any pointers or a tutorial on them?
Looking at the biggest battery(3.7V 6600mAh), and the 6V 3.4W Solar panel(in theory 616 MA, description shows 550, just doing a quick calculation that ignores losses, it would take 12.5 hours of peak sunlight to charge I think, so in reality like 2+ days of keeping it pointed at the sun?
I jumped to that battery, since it would charge my phone 2 times I think, from the mintyboost calculations. My phone battery is labeled 3.7 v 6.66 Wh, so it would be 1800 mAh.

Just looking at it, the panel "might" provide just enough power to charge my phone once a day. That is if it was kept carefully aligned with the sun. Looking at the description of the solar charger, it's designed only for the panels in the store, which have output up to 550 mA, but the charger is capable of up to 1A output. Need either a bigger panel, or a circuit with 2 solar panel inputs.

Unless I've made a drastic mistake somewhere

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adafruit_support_bill
 
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Re: Solar mintyboost calculations

Post by adafruit_support_bill »

Your calculation sound reasonable. The missing information is the amount of unobstructed sunlight in your location. Clouds, trees & nearby tall buildings can all shade the panel and reduce output.

Multiple panels are possible, but you should use blocking diodes to prevent reverse current in the event that one panel becomes shaded.

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kevinrs
 
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Re: Solar mintyboost calculations

Post by kevinrs »

I was searching to find what diodes would be used in a multi-panel setup, and half of what I'm finding is saying that the voltage doesn't vary much with varying light, and with 6 volt systems, the loss from reverse current through even a fully covered panel is less than the loss from the voltage drop of the diode. These say that with 12 v and higher setups, a blocking diode becomes useful.
I might try to calculate this myself, but it's late, and I think I'd need some solar panel data I don't have anyway.

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adafruit_support_bill
 
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Re: Solar mintyboost calculations

Post by adafruit_support_bill »

the voltage doesn't vary much with varying light
That is true of an unloaded panel. But the power output varies and if you draw too much current the voltage collapses. http://learn.adafruit.com/usb-dc-and-so ... sign-notes
the loss from reverse current through even a fully covered panel is less than the loss from the voltage drop of the diode.
Really? I suspect they are talking about larger panels. The voltage drop on high-current power diodes as used in large-scale systems might exceed a volt, but most small-scale silicon diodes are in the 0.7v range. Schottkeys are more like 0.2v.

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