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Solar Charge Controller The previous version of this device used
pulse width modulation (pwm) to control the power from the five solar
panels to charge the battery bank. Under full sun conditions the
MOSFETS got a bit warm and the whole unit radiated a lot of RFI.
This design uses a set of relays - one for each panel. If the
controller decides the battery voltage is too low, it engages another
relay; if its too high, it drops one out. This tends to 'float'
the voltage at about 14 volts as long as sufficient sunlight is available.
The complete schematic and source file are available for download.
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The controller also implements a network
style interface (open collector TTL, 9600 baud). This makes it
possible to 'tweak' the charge settings using a terminal program and
an RS-232 to TTL interface (coming to this web site soon). If
you choose to duplicate this device, you may leave out the network stuff
and 'hardwire' the charge settings in software. 