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'Possible problems using solar panel to power PIC'
2005\08\30@142142 by John Nall

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While I have some confidence in my ability as a programmer, I have no
confidence at all in my knowledge of electronics (not that I don't give
it my best shot, though).  So would appreciate any comments on a little
scheme I am thinking about.  Without going into the messy details, it
will involve a PIC which will get no power except from a solar panel.  
The voltage from the panel will go to a voltage regulator (probably a
7805) to power the PIC.  The idea is that the PIC will start its work
when the sun comes up and raises the voltage from the panel high enough
to start things.  When the sun is going down, voltage from the panel
will continue to drop (and eventually cease altogether) and the PIC will
go off.  It is a non-critical application, and so long as I get 4 or 5
hours of operation on most days, that will be fine.

Now this seems too simple, so I figure I must be missing something.  
Does anyone see any possible problems that would make it a non-starter?  
(The project has to do with a trickle charger for my sailboat, which
normally has no access to shore power).

John

2005\08\30@163514 by Robert Rolf

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Nothing intrinsically wrong.
Depending on your current draw, I would suggest using a low drop out
regulator so that you can use more of the available light energy.

Make sure you have a good LVD (low voltage detect) to ensure a good
reset every time.

Use a nicad on the PIC side, or a very large capacitor on the panel side
so that you can ride out clouds or bird blockages.
With the Nicad, you can probably get enough charge into it during the
day to be able to run all night. With an LM2931-5 reg you can put 4
nicads on the Vcc (4.8v) and they will charge straight off the bus.

Or you could just run the a PIC in low power mode off your
charging battteries.

John Nall wrote:

{Quote hidden}

2005\08\30@171439 by John Nall

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Robert Rolf wrote:

> > With the Nicad, you can probably get enough charge into it during
> the day to be able to run all night. With an LM2931-5 reg you can put
> 4 nicads on the Vcc (4.8v) and they will charge straight off the bus.
>
> Or you could just run the a PIC in low power mode off your
> charging battteries.

Yes, the first thought was to run the PIC off the charging batteries,
but then it occured to me that (a) no need whatsoever for  the PIC to
run at night, and (b) when the power comes up in the morning, that will
automatically reset the PIC (with MCLR tied to power, of course, which
went off the night before).  Since sometimes a few weeks go in between
my visits to the boat, it probably would be good to have it reset every
day, just on general principles (I would think).

Joohn

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