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Charge Controller Types
There are three common types of photovoltaic charge
controllers available today.
Each has it benefits and limits, the choice of controller is
best determined by the specific application.
All of the charge controllers pictured on this page are currently in
operation at our location.
Flexcharge mod. NC1230L12 photovoltaic
12 volt system voltage and 30 amp capacity
with a 12 amp dusk to dawn output for lighting.
Controller can be set for either a 12 or 24 volt battery/load system.
Requires a diode on one of the panels for the night time
function to operate.
The diodes are above the controller, just outside of the picture.
This runs all of our security lighting up front.
Flexcharge PV7D 12 volt / 7 amp dual battery
photovoltaic charge controller.
Charges one or two batteries, puts the power where
it is needed most and isolates the batteries.
These are the earliest kinds of pv charge controllers.
It monitors the battery voltage and when the voltage comes up to a
pre-set point, it disconnects the pv modules.
When the battery voltage settles down it reconnects the modules.
Some controllers use the output wires to the battery to monitor the
voltage while others have separate sense wires to monitor the battery
Widely used today for many applications.
These are very gentle on the batteries, usually requiring less replacement water.
No radio frequency interference generated to interfere with nearby electronic
Some models will perform a micro-equalization charge at the end of each
Very efficient - no cooling fins required to draw heat out of the unit.
Some units will accept different types of power sources at the same
time such as pv modules and a wind or hydro generator.
If the batteries are drawn down to a very low state of charge, this type of
controller will charge them, unlike some PWM charge controllers.
Some controllers of this type have a diversion load output. When the batteries
are full, the controller disconnects the incoming power and diverts it to a
heating load. When the battery voltage settles down, the controller will start
sending the incoming power to the batteries and disconnect the diversion
For long term battery maintenance, these are very gentle and cause the least
amount of electrolyte loss.
Some models require that the pv module or the incoming wire requires a
blocking diode to prevent back-feeding from the batteries to the modules at
Can not perform sustained high voltage equalization charges.
Most will not recharge heavily worked batteries as quickly as a PWM
Pulse Width Modulated or PWM Controller:
Morningstar ProStar 48-15M
48 volt / 15 amp charge controller with a display meter
and push button control in upper right hand corner.
Can be set for different types of batteries and has a low-voltage
disconnect for loads.
This system, when finished, will have three 48 volt solar
arrays - each having its own controller.
This is an old Morningstar ProStar-20 charge controller
(made in the U.S.A.).
12 or 24 volt, this one is on a 12 volt system.
Has a 16 amp low voltage disconnect load output.
Morningstar SunSaver-20 controller.
12 volt / 20 amp and low voltage load disconnect output.
Morningstar TriStar - 60 photovoltaic charge controller.
This system has two controllers which are set up for
charging a 12 volt battery bank from multiple photovoltaic
We have remote monitor displays for each controller over
one of our desks.
These controllers pass the charging current through to the
batteries in high voltage spikes.
The battery voltage is either monitored through the output
wires to the batteries and some higher end units have separate
These can often recharge batteries somewhat faster than an
on/off type of controller.
Some have automatic equalization cycles that will operate every
seven to ten days or when the batteries have been drawn down
to a low state of charge.
A few models have output voltage pre-sets which can be set for
the type of the batteries in the system.
Many units over 10 amps have heat sink fins to dissipate the heat
generated internally - this is power that does not reach the batteries.
These can be very hard on batteries and PWM charged batteries
usually lose more water than other types of charge controllers.
When connected to a battery or battery bank that gets little
use, these can cause the cells to lose water fairly quickly -
Bogart Engineering's SC-2030 pwm controller is limited to
reduce water consumption.
The PWM method creates radio requency interference which can
be great enough that one manufacturer shows how to modify the
unit into an on/off controller if it nterferes with other equipment .
Most 12 volt units require a minimum of eight volts at the battery
before it will function - this means that if you batteries are drawn
down too low, a PWM controller can not feed power into the
batteries regardless of how much is available from the pv modules.
On systems that are left for long periods of time
without a load being applied, the pwm
controllers can be rough on the batteries.
They keep pulsing high voltage spikes into
the battery and can cause excessive water loss
- yes, I am repeating myself.
Always read the instructions before installation - every PWM controller I have handled
requires that the battery be connected before the panels are connected.
These controllers require a battery voltage to start their functions.
When we used to sell Morningstar controllers we would get at least one call or e-mail a
week from a customer who did not read the instructions and said the controller did not work.
I would tell them that the battery had to be connected first and give them the page number in
the manual showing this.
Maximum Power Point Tracking Controller:
Solar Converters mod. PT48-8P48B12/24 charge controller mounted outside
in a rain-tite enclosure.
This is set up to allow high voltage pv modules to charge a 24 volt battery
These made their debut many years ago and have shown that in some
applications these will do the job when nothing else will work.
In effect, this controller hides the batteries from the pv module which allows
it to operate at a higher voltage than the other kinds of charge controllers.
Take a nominal 12 volt pv panel, it will have an open circuit voltage of around
20 to 22 volts and a maximum power voltage of around 17 to 18.5 volts.
A conventional charge controller will allow the battery to draw the voltage
down to around 14 volts.
An MPPT controller will allow the panel, if there is enough sunlight available,
to operate in the maximum power point (sweet spot) voltage/amperage range
on the power curve.
This can allow the panel to output near or at the rated wattage.
Some controllers can take a much higher panel voltage and drop it down
to the battery system charging voltage.
In very cold and sunny situations these controllers can extract the most from
the pv module.
Where the pv modules have to be located a long distance from the batteries
they can be wired in series to increase the output voltage (which will require
a smaller wire size and have less voltage drop) and then the controller will drop
the voltage down to charge the batteries.
In this application no other type of controller will work.
These are usually much gentler on the batteries than the PWM type controllers.
They can also be custom built for use with grid-tie photovoltaic modules that have
odd ball voltages. This allows these panels to be used for charging batteries.
In low light levels, early in the morning, late in the afternoon or on overcast days,
the controller may output little or no power to the batteries.
In low light conditions the pv panel may not be able to produce the maximum
power voltage that the controller is looking for.
It will search for the sweet spot but not find it until the sunlight increases.
A conventional charge controller can often deliver a charging current to the
batteries when an MPPT controller can not.