A charge controller, also
known as a solar regulator, is a
regulator that goes between the solar panels
and the batteries. A charge controller
is used to regulate the voltage and current
coming from the solar panels and going to the battery. As
the input voltage from the solar array rises, the charge
controller regulates the charge to the batteries preventing
any over charging.
A controller can also provide a direct connection to appliances,
while continuing to recharge the battery.
Modern charge controllers use pulse width modulation
(PWM) to slowly lower the amount of power applied
to the batteries as the batteries get closer and closer
to fully charged. The newer Maximum Power Point
Tracking (MPPT) controllers are even better.
MPPT charge controllers allow your solar panels
to operate at their optimum power output voltage, improving
their performance by as much as 30%. They can also match
the output of the solar panels to the battery voltage to
insure maximum charge (amps). MPPT charge controllers are
more expensive that PWM charge controllers, but the advantages
are worth the cost. If you can afford it, you should definitely
use an MPPT charge controller.