The most basic charge
controller disconnects the array when the battery is fully charged and keeps the
battery fully charged without damage.
Charging regimen required is different for
each battery type. Different charge are required for Lead Acid (liquid), GEL AGM
or VRLA and yes Lithium Ion batteries.
Series controllers stop the
flow of current by opening the circuit between the battery and the PV array. The
more advanced version of this is called Pulse Width Modulation (PWM)
MPPT (Maximum power point
tracking) charge controllers use both PWM and MPPT. MPPT charge
controllers frequently and continually sample the incoming voltage and amperage
then convert the input to the voltage and amperage required by the
batteries at the current requirement for this stage within the charging cycle.
The most efficient technique used in MPPT sis called Perturb and observe. It
essentially means that the incoming volts and amps are interrupted, analyzed and
reconfigured for optimum output at this stage of charging. (you really don't
need to know this bit but you can search "MPPT Perturb and Observe" on the
internet if you're so inclined).
Shunt controllers divert
the PV array, hydro or wind current from the battery to an electrical load. This
technique is mandatory for wind and water turbines as these would be damaged if
operated without a load. Many charge controllers have facility to provide
power to a load based on voltage, time and power coming in from the solar
panels. These are not shunt loads to divert power in order to avoid over
Input voltage: Solar
panels operate at higher voltages than batteries and most PV allows even higher
voltages by wiring several panels in series.
Simple, series controllers have the same input and output amperage. MPPT
charge controllers, because the convert incoming power will have lower output
voltage to match the battery's charge requirement but because of the equation
Watts=V*A as voltage is reduced Amperage goes up. Charge controllers are rated
by the Volts and Amps they can handle. Make sure that with a MPPT charge
controller that you calculate output amps.
Each battery type from Flooded Lead Acid to Lithium Ion has different charge
requirements and restrictions.
Battery voltage: Currently
system battery voltages range from 12 to 72V. The most popular off-grid
system voltages are 24 and 48 volt.
In general the least expensive charge controllers are the least efficient.
Look for an MPPT charge controller for more efficiency. Read the manufacturer's
specification. Efficiencies range up to 98% power conversion.
First comes capacity, if you think you will want more solar panels later,
consider purchasing the additional capacity now. Two controllers that
don't communicate with each other will cause one to fool the other as one will
be fooled by the other's charging. Many top tier controllers have methods
of connecting to each other. Some of these connections require nothing
more than a telephone jacked cord (e.g. Midnite), others require special wiring
and additional equipment (e.g. Outback). MidNite Solar has a 30A MPPT
charge controller that is able to share the incoming power from PV on the same