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Solar Boost Bag: overload PowerBoost 500?
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Solar Boost Bag: overload PowerBoost 500?

by colemanjj on Mon Jun 25, 2018 3:18 pm

Reading over the project I see the PowerBoost 500 is connected to the load and ground pins of the solar charger. From other projects I gather that the load pin can be > 5 volts because, if the battery is full, the solar panel goes directly to the load pin.
With a 6 volt solar panel there could be 6-7 volts at the load pin of the solar charger. The specs for the TPS61090 in the PowerBoost is for a max Vin of 5.5 volts. Two questions:
1) Is it safe to overload the PowerBoost 500 with 6-7 volts? and,
2) Will the PowerBoost 500 bring the voltage from the solar panel down to the USB standard of 5-5.5 volts?

I don't want to fry my phone if the voltage at the USB output is too high.
thanks, john

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Re: Solar Boost Bag: overload PowerBoost 500?

by adafruit_support_mike on Wed Jun 27, 2018 4:37 am

Your phone isn't in any danger. The PowerBoost's output won't go above 5.2V

It's technically possible for the solar panel's output voltage to rise above 6V, but the nature of the circuit makes it unlikely. The panel's output voltage falls when the load draws more current, and the boost converter draws a lot of current. If that's active, the large solar panel can generate just about enough current to maintain 6V output while the PowerBoost's output is 1A @ 5V

The TPS61090's maximum recommended input voltage is 5.5V, but its absolute maximum is 7V. You'd need a lot of light on the panel and no activity from the LiPo charger or boost converter to get near that.

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Re: Solar Boost Bag: overload PowerBoost 500?

by colemanjj on Thu Jun 28, 2018 1:05 pm

thanks,
This explanation is very helpful. I'm soon heading out on a cross-part-of-the-country bike trip and don't have time to put this charger together. But maybe I'll get it together for the return trip.
john

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