Solar USB charger
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Solar USB charger

by OmegaDestroyer on Thu Mar 21, 2013 5:21 pm

Hi,
I'm looking to make a solar only USB charger. The various projects I find here all seem to charge a battery then a device.
I'm looking to go straight from a solar panel to the device without the need for any other batteries in between.
Does adafruit offer some sort of regulator that will allow me to do that?
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Re: Solar USB charger

by adafruit_support_bill on Thu Mar 21, 2013 5:41 pm

What device? What panel voltage? Can you tolerate intermittent operation?

There are lots of buck and/or boost converters that can work in ideal conditions. But solar power is variable and solar panel output can drop dramatically with a passing cloud. That is why most projects use batteries as a buffer.
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Re: Solar USB charger

by OmegaDestroyer on Fri Mar 22, 2013 2:15 pm

The device will probably be a tablet of some sort (I haven't purchased it yet), but it will be a non-apple product.
I will be backpacking in the summer but will have limited access to electricity. I just needed something to attach to the outside of the bag and charge while I walk around.
It doesn't need to provide the most stable current, so maybe just a capacitor as a buffer will do. I'm guessing a 6-7 volt panel with a 200-300 mA output should be sufficient to charge a device.
I think all I need is a voltage regulator maybe attached to a capacitor and diode.
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Re: Solar USB charger

by adafruit_support_bill on Sat Mar 23, 2013 5:27 am

I tried something similar a few years ago. I had a 12v 3W flex-panel lashed to my pack with a 5v buck converter and a cable for my phone. The experiment was a failure.

The problem is that charge controllers for LiPo cells DO expect a stable voltage source. For safety and battery life, the charge controller doesn't just pump current into the cell when it is available, it implements a charge cycle that starts slow, ramps up and then tapers off to the end. If the power fluctuates too much, it disrupts that charge cycle and it has to start over again. The net result with my phone was that it never got much of a charge.
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Re: Solar USB charger

by dmpyron on Wed Apr 17, 2013 2:51 am

Well, at the fear of offending the good Lady :D , Costco has a "kit" that has a flex cell that you can put on a back pack and either run your goodies directly off of it or charge a battery. It even comes with a small lantern! I'm giving it a little thought.
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Re: Solar USB charger

by john444 on Wed Apr 17, 2013 6:17 pm

Hi Dmpyron,

Omega Destroyer indicated he/she wanted something to directly charge a cell-phone.
OmegaDestroyer wrote:I'm looking to go straight from a solar panel to the device without the need for any other batteries in between.


You seem to be saying that the Cosco kit will charge a cell-phone directly from the solar-panel.
dmpyron wrote:Costco has a "kit" that has a flex cell that you can put on a back pack and either run your goodies directly off of it or charge a battery.

However the Costco kit includes 4 AA rechargeable batteries that probably are used in the same way that the Solar LiPo charger / Minty-Boost work.

I am pretty confident that you will be unable to properly charge a cell-phone directly from Costco's panel (without the rechargeable batteries).
As Lady Ada indicated, the panel's output is not stable enough to maintain the cell-phones charge cycle even if you included a voltage regulator to provide the required 5-V output voltage.

I doubt the good Lady will be offended but she does know her stuff.

John
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