| |
Charge Controller
The purpose of the charge
controller is to charge batteries without overcharging them. The most basic charge
controller disconnect the PV array when the battery is fully charged and keeps the
battery fully charged without damage.
Different charging regimen are required is different for
battery types. Within lead acid batteries different charging is required for Lead Acid (liquid), GEL AGM
or VRLA and yes Lithium Ion batteries.
Controller Types:
-
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 requirement at the current for this stage within the charging cycle.
The most efficient technique used in MPPT is 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 e.g a
heating coil. This technique is mandatory for wind and water turbines as
these would be damaged if operated without a load. Many charge controllers
have ability 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
charging batteries e.g. charging another battery, turning on a light at dusk or
timer.
Selection criteria:
-
Input voltage: Solar
panels operate at higher voltages than batteries and most PV allows even higher
voltages by wiring several panels in series. The advantage of higher voltages is
that Amps are lower, avoiding power loss if the panels are not close to the
charge controller.
-
Current: Simple controllers have the same input and output amperage. MPPT
charge controllers, because can convert incoming power have lower output
voltage to match the battery's charge requirement. Charge controllers are rated
by the Volts and Amps they are able to handle. Make sure that with a MPPT charge
controller that you calculate output amps.
-
Battery type:
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.
-
Efficiency:
In general the least expensive charge controllers are the least efficient.
Look for an MPPT charge controller for more efficiency. If these are beyond your
budget consider a PWM based charter. Read the manufacturer's
specification. Efficiencies range up to 98% power conversion.
-
Expandability:
First comes capacity, if you think you may want more solar panels in the future,
consider purchasing the additional capacity now. Unless you invest in a
charge controller that can communicate to another expanding later will require
the original charge controller to be replaced. Two controllers that
don't communicate with each other cause one to fool the other as one will
start sooner and will fool the second one to 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 Solar), others require special wiring
and additional equipment (e.g. Outback). MidNite Solar has a 30A and 90A MPPT
charge controllers that are able to share the incoming power from PV.
|
