OH Photovoltaic Charger

Phil Endecott spam_from_qihw at chezphil.org
Sun Jul 18 12:39:05 EDT 2010

Marco Castorina wrote:
> what I really miss
> for my laptop is a photovoltaic charger that would allow
> me to use it in parks or open air in general

I have a nominally 6V 1.5W solar panel of approx A5 size with a USB A 
socket.  It's similar to this widely-available one but without the case:


When I connect this directly to the NN, the charging LED comes on when 
it's in direct sunlight and the terminal voltage is around 4.15V.  
Unfortunately I can't easily measure current; since the Li-ion charging 
voltage is 4.2V, it's possible that it is just floating without any 
useful current going anywhere.

In cloud the light goes out and the voltage drops to below 3V.

Generally, charger ICs do not say much about how they will behave when 
the input is variable or feeble, as it is with a solar panel.  Perhaps 
partly because of this, most solar chargers for things like phones have 
a battery; the panel charges the battery and the battery later charges 
the device (which it can do with a reasonably constant high-current 
output).  But this is inevitably less efficient than connecting the 
panel directly to the device.

I wanted to look at the schematics for the NN's battery circuitry.  So 
I went to the wiki, but I wasn't able to find them.  Can anyone point 
me in the right direction?

Cheers,  Phil.

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