Build an Inexpensive
Solar Trickle Charger
by Alan Federman
From Junk
Lots of my robots run outdoors in bright sunshine, so it
would help if they could harness those rays. Hey folks, it’s
raining soup, so get yourself a pail! Custom store-built
chargers are expensive and you may not get the exact voltage
match to your particular battery setup. For example, a good
charge rate for a 12V lead acid battery is about 14. 6 volts. The
solar cell I had put out 24-27 volts. Buying an adjustable regulator
is expensive, plus you have to worry about designing a complicated circuit to make sure the battery isn’t over or under charged.
Fortunately, there is an easy trick called ‘floating the ground’
that can make an inexpensive 12V regulator put out exactly the
voltage you need. Twelve volt regulators are very common — for
example, the 7812 type which is probably hanging out in some
of your busted PC power supplies. It can be easily salvaged or
purchased for a couple of bucks. The other item you’ll need are
four power diodes. Both are staples at RadioShack.
Refer to the diagram in Figure 1. Depending on the size of the
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