What does a charge controller do?
A charge controller, or charge regulator is similar to the voltage regulator
in your car. It regulates the voltage and current coming from the solar
panels going to the battery. Most "12 volt" panels put out about
16 to 20 volts, so if there is no regulation the batteries will be damaged
from overcharging. Most batteries need around 14 to 14.5 volts to get
Why 12 Volt Panels are 17 Volts
The obvious question then comes up - "why aren't panels
just made to put out 12 volts". The reason is that
if you do that, the panels will provide power only when
cool, under perfect conditions and, full sun. This is not
something you can count on in most places. The panels need
to provide some extra voltage so that when the sun is low
in the sky, or you have heavy haze, cloud cover, or high
temperatures*, you still get some output from the panel.
A fully charged battery is around 12.7 volts, so the panel
has to put out at least that much under worst case conditions.
Charge controls come in 3 general types (with some overlap):
Simple 1 or 2 stage controls which rely on relays or shunt transistors
to control the voltage in one or two steps. These essentially just short
or disconnect the solar panel when a certain voltage is reached. For all
practical purposes these are dinosaurs, but you still see a few on old
systems. Their only real claim to fame is their reliability - they have
so few components, there is not much to break.
3-stage and/or PWM such Morningstar, Xantrex, BZ Products, Blue Sky,
Steca, and many others. These are pretty much the industry standard now,
but you will occasionally still see some of the older shunt/relay types
around, such as in the very cheap systems offered by discounters and mass
The maximum power power tracking ones (MPPT), such as those made by Blue
Sky Energy and Outback Power. These are the ultimate in controllers, with
prices to match - but with efficiencies in the 96 to 98% range, they can
save considerable money on larger systems since they provide 15 to 30%
more power to the battery. For more information, see our article on MPPT.
Most controllers come with some kind of indicator, either a simple LED,
a series of LED's, or digital meters. Some newer ones, such as the Outback
MX60 and a few others now have built in computer interfaces for monitoring
and control. The simplest usually have only a couple of small LED lamps,
which show that you have power and that you are getting some kind of charge.
Most of those with meters will show both voltage and the current coming
from the panels and the battery voltage. Some also show how much current
is being pulled from the LOAD terminals.
Trace C-35, C-40 and C-60 Controllers
The Trace C-35, C-40, and C-60 PWM controllers can be used as a PV charge
control, DC load control or DC diversion regulator in 12, 24 and 48 volt
systems. They operate in only one mode at a time, so to provide both PV
charge control and low battery load disconnect, two controls must be used.
As a DC load control they disconnect the load at a user settable low voltage
and reconnect at the low voltage reconnect point. As a diversion controller
they send excess power to a "dummy load" such as a water or
space heater to regulate hydroelectric or wind generators. All the Trace
controllers, when used as a charge control, have field-adjustable bulk
and float setpoints and perform automatic equalization every 30 days or
whenever LVD is reached. Equalization can be manually initiated. Order
the optional temperature sensor for more accurate battery charge control.
The optional LCD Digital Display shows battery voltage, array amps and
watts, cumulative amp-hours and a separately resettable "trip"
amp-hour measurement. The digital display is available for mounting on
the front of the charge control, or with a 50 or 100 foot cable for remote
mounting in a double-gang electrical bos. UL listed