Charge Controllers Information
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For help selecting your charge controller
please email
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What is a charge controller ?
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A charge controller is
a piece of equipment designed to prevent the batteries in
your system from overcharging. It is similar to the voltage
regulator in a car. A typical 12 volt solar panel is capable of producing up to 19 or 20 volts. If the panel
was left connected to a 12 volt battery with no charge controller, the battery voltage would
continue to rise until the battery is damaged. A charge controller can maintain healthy battery voltage
by either short circuiting the solar panel, disconnecting the solar panel from the battery or by
diverting the excess electricity to a load such as an air heater, water heater or other electrical
load. Solar electricity can be either disconnected or diverted. Wind turbines and water
turbines must remain connected to the batteries at all times so their electricity must be diverted
or dumped in order to protect the batteries.
There are currently four types of charge controllers on the market today:
Do I even need a charge
controller?
Shunt type charge
controllers- these are the first to be developed and most
crude form of charge controller on the market today. They are only used as solar charge controllers (not for
water or wind power). They shunt (or short circuit) the energy from a solar panel when the battery is full.
These controllers have a set on and off voltage with a hysteresis (difference) sometimes adjustable by the
user and sometimes factory preset. When the batteries hit the high voltage setting the entire electricity
source is shunted (short circuited) until the voltage hits the low voltage setting. This keeps the batteries
regulated but the voltage can vary between the on and off settings. They are the least accurate type of
controller.
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Relay type charge controllers - these were
the second type of charge controller to be developed. They are similar in function to
the shunt type except instead of short circuiting the panel output they open circuit between the
solar module and the batteries. These controllers have a set on and off voltage with a hysteresis
(difference) usually adjustable by the user. When the batteries hit the high voltage
setting the entire electricity source is disconnected until the voltage hits the low voltage
setting. This keeps the batteries regulated but the voltage can vary between the on and off settings
and is not that consistent. These also can only be used as a solar charge controller (not for use with water power or wind power). |
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PWM (Pulse Width
Modulated) charge controllers - This style of charge controller keeps the batteries regulated by
disconnecting and reconnecting portions (or part) of the electricity available from the solar module
several times per second keeping the battery voltage more constant. With the development of
these charge controllers came a new
and improved way of charging batteries using a bulk,
absorption,
float and
equalization charge. These
are a great improvement over relay charge controllers as they are able to keep the battery voltage
much more stable. They do not increase the output of the solar array but are more efficient than the
previous controllers. Aside from being a charge controller, these units can have many features
including digital
displays, remote
displays, load control, lighting
control,
and diversion
control. |
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MPPT (Maximum Power
Point Tracking) charge controllers - This style of charge controller uses pulse width
modulated technology to keep the batteries regulated but is able to also increase the output of
the solar array by finding the maximum power point of the array (which is a higher voltage than
the battery bank) and reducing the voltage to charge the batteries. This can result in up to a
30% increase in output of the solar array. It also allows for a higher voltage transmission from
the solar array to the controller keeping wire losses to a minimum. Outback Power' s
FM60 MPPT charge controller is
our favorite as it is useful over a wide range of voltages and super efficient. Aside from being
an MPPT charge controller, these units can have many features
including digital displays, remote displays, load control, lighting
control, diversion
control and
an extra programmable
relay. Some of these charge
controllers can accept voltages up to 150 volts DC to make long distance transmission possible and
efficient. There are MPPT controllers being designed now that are capable of input voltages up to
200 volts DC. Read about these NEW developments in charge
controllers . MPPT technology is
constantly being improved and is very exciting for our industry. Learn more about MPPT
technology. |
Today's charge controllers do more than just maintain correct battery voltage.
Some charge controllers features include:
| Digital Display
- Some charge controllers have an optional or
included digital display on the front of the unit. This display shows the user how many volts, amps
and/or watts the system is generating as well as keeps track of total power production and other
pertinent info as available. To the right is an photo of an installed front mount display for an
Xantrex C40 and C60. |
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| Remote Display
- Some charge controllers include, or have as an
option, a remote meter that can be installed in another room or building. They usually display the same
info as the installed digital displays but can be more conveniently located for easy
access. |

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| Load
Control - To prevent a battery from becoming deeply
discharged by a load (such as a light or motor), a load controller is used. The load controller
monitors battery voltage and disconnects the load from the battery at the disconnect voltage and does
not reconnect the load until the battery reaches the reconnect voltage. These on and off settings are
usually user adjustable. Common settings would be to disconnect at 10.5 volts and reconnect at 12.5
volts. Many charge controllers have a load control feature but can only be used as a charge controller
or a load controller, not both. Two controllers would be required to perform both functions. Two
exceptions to this are Morningstar's SunSaver
SS-6 and SunSaver
Duo dual function charge and load
controllers. |
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| Lighting Control
- A lighting controller is a charge controller used
to control lighting. They have several lighting functions such as dusk to dawn lighting or other on and
off settings. They are used for security lighting, home lighting and billboard lighting. They are
microprocessor controlled, fully automatic and also act as a load controller to protect the battery
from deep discharge. Morningstar's
SunLight charge controller is an example of a good
quality lighting controller. |

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| Diversion (Dump)
Control - When charging a battery with a solar panel
the energy source (solar panel) can simply be disconnected to regulate the
voltage. When charging the battery with a water
turbine or wind turbine the energy source cannot be simply
disconnected. This would overspeed the water
turbine or wind turbine and destroy it. Instead...the turbine is connected directly to the
battery and the excess power is now dumped (or diverted) from the battery to a water or air
heater using a diversion controller. This type of controller monitors the battery voltage and
diverts all or a portion of the produced energy as heat to the dump load. The dump load can
either be a useful load (like a hot water heater) or not useful and be dumped into an outside air
heater. Many charge controllers have a diversion control feature but can only be used as a charge
controller or a diversion controller, not both. Two controllers would be required to perform both
functions. The Morningstar TS-45 is an example of
a good quality diversion controller. We now stock a variety a diversion loads. |
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Extra Programmable Relay - Outback Power System's
FM60, OutBack Power System's FM80
and Xantrex's MPPT60-150 charge controllers have a user programmable relay that can be adjusted to
perform many functions. The relay can be used manually as a switch for pretty much anything you
want to control remotely or the relay can be used as a diversion controller, a lighting controller,
a load controller (with an optional solid state relay). Another option is to use it to control an
exhaust fan for your battery enclosure or an alarm to tell the user the batteries have not been
charged for a set amount of time.
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| Remote Temperature Sensor
- An RTS or remote battery temperature sensor is used
for temperature compensated battery charging. As a battery gets warmer gassing increases. As a battery
gets colder it becomes more resistant to charging (requires a higher voltage to charge). The more the
temperature changes, the more important a battery temperature sensor is. The image on the right is an
Xantrex RTS used for the C40, and C60 charge controllers. |

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- Bulk Charge - The bulk
charge is the beginning of the three step process of most advanced charge controllers on the market today.
During the bulk stage all current available from the solar panel is applied to the battery until the battery
reaches the preset absorb voltage as specified by the charge controller or user. At this point the charge
controller enters absorbing mode. For a 12 volt nominal lead acid battery this voltage might be anywhere from
14.0 - 15.0 volts.
- Absorption Charge - During the absorb stage just enough current is applied to the battery to hold a preset absorb
voltage for a set period of time. This stage is designed to prevent overheating and over-gassing of the
battery. The current is tapered down to maintain battery voltage. The voltage for this mode in a 12 volt system
is 14.0 - 15.0 volts. If the voltage is able to be maintained for the preset period of time the charge
controller will enter float mode.
- Float Charge - During
float mode, a maintenance charge is applied to the batteries until there is no more excess energy available
(the end of a sunny day) The voltage for this mode in a 12 volt nominal lead acid battery will be approximately
13.4 volts.
- Equalization Charge - An equalization charge is a periodic boost charge applied to stir the electrolyte, level the
cell voltages and complete the chemical reactions within the battery. It is usually done at a set period of
time from every month to every three months depending on battery manufacturer recommendations. The higher
quality charge controllers will perform this stage automatically. The voltage for this mode in a 12 volt
nominal lead acid battery will be above 15.0 volts and up to 16.0 volts. For more information on equalization
read our
equalization page.
Do I need a charge controller for my system?
Most systems require a charge controller. However, very tiny systems
do not.
As a general rule you need a charge controller if your solar modules are making more than 2 watts per 50 amp hours
of battery (at the same voltage).
For example: if you have a 12 volt, 120 amp hour battery (a typical
large RV battery), any module 5 watts or less will not require a charge controller.
The formula...
(120 amp hours divided by 50 amp hours) X (2 watts)=4.8
watts.
If your solar module is larger
than 5 watts ...you need a charge controller.
Which charge controller is the right one for me?
First you need to decide what type of controller is suitable for
your application. Things to consider include:
- the distance from your solar array to the batteries. The more
distance, the higher you might want the voltage to keep wire losses to a minimum. In this case consider
an MPPT charge
controller.
- the open circuit voltage of your
panels
- is the voltage of your solar panel the same as the battery
voltage? If not you are going to need an MPPT charge
controller.
- do you need to get every watt possible out of your array? If
yes then you are going to need an MPPT charge
controller.
- is cost the most important factor to you? If yes, you might
consider a PWM
or relay
type charge
controller.
- is this just a very small one panel system? If so
the Morningstar SunKeeper SK-12 might be a good solution.
- is your single panel system 40 watts or less? If so
the Morningstar
SunGuard SG-4 would be a good solution.
Battery Voltage
- Charge controllers come in various sizes (amperages) and
voltages. To choose the correct controller you need to know your system's battery voltage (12, 24, 48 etc...) Most
controllers are designed for either 12, 24, and 48 volt systems or a combination of two or three of these voltages.
Some are designed for only one voltage. Morningstar's Tristar
TS-45 and Tristar
TS-60 are user programmable using a serial
cable, to any battery voltage between 12 and 48, making them suitable for 32 and 36 volts
systems.
Amperage
- All controllers have a maximum current limit. They can be as
small as 4.5 amps and as large as 100 amps. Please note this is the amperage between the charge controller and the
battery and not the input amperage of the solar panel(s). Generally you should size your charge controller at least
25% larger than what is required. This allows the charge controller to operate cool and can also increase the
lifetime of the unit.
Options
- Many charge controllers contain different options. Be sure to
check to check the specification sheet of your controller before making a purchase. It should give you a good idea
of the options available for the specific charge controller. For common charge controller options click
here.
If you would like help choosing the right charge controller please email or call.
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