[aprssig] Solar charging again

Robert Bruninga bruninga at usna.edu
Fri May 6 09:03:25 EDT 2005

>>> <scott at opentrac.org> 5/5/2005 11:07:35 PM >>>
>I hadn't realized the trickle rate was so high on the AAs.  
>So what should my target open circuit voltage be on the 
>panel, relative to the battery voltage?

Generally, it wont matter, since the I-V curve of the
panels is current limited when operating at the voltage
of the battery.   Usually for 12 volt systems, panels
have an OCV of about 18 volts and for 6 volt systems
about 9 volts.  But again, the circuit will never
see open circuit voltage since the batteries will
clamp the voltage to their full charge state...



-----Original Message-----
From: Robert Bruninga [mailto:bruninga at usna.edu] 
Sent: Thursday, May 05, 2005 5:14 PM
To: aprssig at lists.tapr.org; scott at opentrac.org 
Subject: Re: [aprssig] Solar charging again

>>> scott at opentrac.org 5/5/2005 6:18:46 PM >>>
> I'm interested in solar charging for small systems...
> The average power... can be kept to under 50 mW.
> The tracker maybe 6 mA at 5 volts...  I figure a
>6" by 6" or smaller panel should be able to do it
> but I'm not sure about the efficiency of small
>charging circuits.

You dont need any circuit.  Just hook the panel to the
battery through an isolation diode.  Reason is, you
want every bit of current into charging and you cannot
possibly overcharge the battery with such a tiny panel.
(assuming you are Using AA cells)...  Also use NiCd's
instead on NIMH since they are less critical to
chargning anomolies...

For AA nicads, the trickle charge rate is probably 50
to 100 mA for 500 or 1000 MAH cells.  So as long
as your solar panel cannot pput out more than
50 or 100 mA, then there is never any problem with


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