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Solar Charge Controllers and Regulators
Charge
Controllers and Regulators
The main function of a controller or regulator is to fully charge a
battery without permitting overcharge and at the same time
preventing reverse current flow at night. Smple controllers
contain a transistor that shunts the PV charging circuit,
terminating the charge at a pre-set high voltage and, once a pre-set
reconnect is reached, opens the shunt, allowing charging to resume.
More sophisticated controllers utilize pulse width modulation (PWM)
or maximum power point tracking (MPPT) to assure the battery
is being fully charged. The first 70% to 80% of battery capacity is
easily replaced, but the last 20% to 30% requires more attention and
therefore more complexity.
How do
controllers work?
The electronic circuitry
in a controller monitors the voltage of the connected battery and
determines the state of charge of the battery. As the battery
nears full charge the amount of current flowing to the battery is
reduced until the battyer reaches its full state of charge.
Features to watch out for with controllers are:
• Low-voltage load disconnect
(LVD) – reduces damage to batteries by preventing deep
discharging.
• Reverse current leakage protection – disconnects the array to
prevent feedback into the solar modules at night.
• System monitoring - analogue or digital display meters,
indicator lights and/or warning alarms.
• Over current protection – achieved with fuses and/or circuit
breakers
• Mounting options – flush mounted, wall mounted, indoor or
outdoor enclosures for all weathers.
• System control – control of other components in the system;
standby generator or auxiliary charging system, diverting array
power once batteries are charged, transfer to secondary
batteries.
• Load control – automatic control of secondary loads, or
control of lights, water pumps or other loads with timers or
switches
• Temperature compensation – utilized whenever batteries are
placed in a non-climate controlled space. The charging voltage
is adjusted to the corresponding temperature.
• Pulse Width Modulation (PWM) – an efficient charging method
that maintains a battery at its maximum state of charge and
minimizes build-up of sulphur by pulsing the battery voltage at
a high frequency.
• Maximum Power Point Tracking (MPPT) – a new charging method
designed to extract the most power possible out of a solar
module by altering its operating voltage to maximize the power
output.
Sizing
the Controller?
Q. Do I need to fit a regulator?
A. Yes. It is
recommended
a regulator
is fitted
if the
minimum ratio of 10W of solar panel to 100Ah battery capacity
is exceeded.
Q.
How do I calculate the Amp rating of the regulator needed?
A. Employ the physics equation of Amps x Volts = Watts
P= V x I. Power (Watts)
= Voltage (V) x Amps (I).
Charge controllers are rated and sized according to the solar array
system voltage and current. The most common solar array system
voltages are 12, 24 and 48 volt and controllers are rated
accordingly. Controller operating voltages vary from 6 - 60
volts and from 1 - 60 amps. For example, if you have 2 x 85W, 12V
solar panels and one module produces 5.34 amps, your combined (2
panel) system will produce 10.68 amps at 12 volts. Because the
current of a solar panel varies with temperature, light reflection
and other factors could lead to sporadic increased current levels.
Because of this the operating current of a controller is increased
by at least 25%. This means that in our example the controller must
be able to accommodate at least 13.35 amps. A 15 amp or greater,
rated solar controller would be used to handle the current flow from
our example. NOTE: it makes sense to allow for additional capacity
to be added to your system and would therefore make sense to select
either a 20A or 30A solar controller.
Q.
What is state of charge and how is it
measured?
Take for example the performance of Steca products. They are shown by the accuracy of the
state of charge (SOC) measurement, which results in the long
lifetime of the battery.
Q.
What does SOC mean?
The SOC (State of Charge) indicates
the actual charging status of the battery. If the battery is fully
charged the SOC is 100 % - if it is completely empty the SOC is 0 %.
All values in between are possible, but a lot of battery types
should not reach SOC values less than 30 %. It is important not to
confuse the SOC with the capacity
of the battery. The SOC does not reflect the remaining capacity of
the battery. The actual remaining capacity of the battery is
influenced by a lot of parameters besides the SOC. Multiplying the
SOC with the nominal capacity of the battery results in information
about the residual capacity of the battery. This value does still
not reflect the remaining capacity accurately due to various other
parameters including the age of the battery.
Q. Why is SOC calculation
important?
If a battery is charged, the charge controller needs to know if it
is full to prevent a batteries damage due to over charging. While
discharging, the controller needs to know if the battery is empty in
order to prevent dangerous deep discharging. There are several
possibilities to determine if the battery is full or empty. The most
common criterion is the voltage of the battery. A certain fixed
voltage is set to disconnect the load and protect the battery.
Unfortunately this criterion is improper. Especially in solar
systems, low discharging currents are common and lead to improper
battery maintenance if a fixed voltage for load disconnection is
used. Better solutions also take the charging / discharging current
into account to determine if the battery has to be disconnected from
the load. But also this method does not allow an adequate load
disconnection to protect the battery optimally due to a very low
accuracy and a high error rate. A lot of additional parameters, like
temperature, the age of the battery, the user behaviour and other
values, influence the battery.
Only an accurately calculated state of charge allows to disconnect
the load correct according to the properties of the battery. This is
why Steca developed a powerful and precise algorithm to determine
the actual state of charge of a battery.
Q. How does the Steca SOC
algorithm work?
The Steca state of charge algorithm
is a combination of different methods in order to ensure a precise
calculation combined with a stable long time performance. Cost
optimised product realisation is additionally another important
point for Steca. Years of experience in this field and important
research activities led to a self learning „fuzzy logic“ algorithm.
It takes into account the user behaviour and the ageing of the
battery. The voltage of the battery, as well as all battery
currents, are watched closely by the charge controller in
combination with the temperature. The charger approximates the SOC,
during a learning period which takes place in the first cycles. By
monitoring the battery and adapting parameters to the changes, a
self learning algorithm results that is also able to take the use of
the battery into account. This characteristic makes the Steca SOC
algorithm a powerful and reliable function, which will ensure the
correct monitoring of the battery. The user benefits from a fast and
precise information about the battery status that is displayed on
the charge controller. Finally the user benefits from the most
important advantage to enlarge the life-time of the battery with the
help of an optimised battery maintenance.
Q. Which chargers from
Steca carry the optimised algorithm?
The Steca product range is divided
into two lines. One is optimised for use in simple applications with
less demand and equipped with the minimum necessary features. The
other line is designed to cover high-end demand to supply a good
communication interface to the user and optimised battery
maintenance features. For both lines there exist charge controllers
in a wide power range. Charge controllers in a wide power range
exist for both lines. All chargers that are equipped with the
special Steca State of Charge algorithm are marked with the SOC
symbol in this catalogue.
State of Charge
Example
The graph shows the properties of a
28 Ah lead acid battery in relation to the charging / discharging
current, the voltage and the state of charge. If the full battery is
discharged with 50 A and a load cut off voltage of 1.85 V/cell is
applied (equal to 11.1 V for 12 V battery) the load will be
disconnected at around 70 % state of charge. This means the battery
is still quite full but the load can no longer be supplied due to
deep discharging protection. If it is discharged with 5 A, the
voltage of 11.1 V will lead to a disconnection at 10 % state of
charge which is already a dangerous deep discharge for the battery.
With the Steca SOC algorithm the load will be disconnected along the
line of 30 % SOC in dependence of the discharging current at the
cross with the discharging current line. Only this complicated
procedure can ensure optimal battery maintenance.
Q. How is a
regulator used in a home solar system?
System Overview
A Solar Home System consists of a
Steca Solar charge controller, a battery, a solar module and the
load. The load is always a DC load in standard Solar Home Systems.
The charge controller is connected directly to the battery. The
module and the load are connected directly to the charge controller
terminals. Steca controllers regulate the complete energy flow
within the system. The battery is charged by the current from the
solar module. If the battery is full, the charge controller limits
the current to the battery to protect the battery from over
charging. If the load discharges the battery, the controller also
cuts off the load before the battery is empty, in order to prevent a
dangerous deep discharge of the battery. Steca controllers also have
an integrated intelligent battery monitoring system. The optimal
charging strategy will be chosen depending on the need of the
battery. In Solar Home Systems the charge controller is the central
device – all functions of the system are influenced by this
controller. Due to this fact it is important to choose a good
controller.
Q. How is a
regulator used in a stand alone inverter system?
System Overview
Stand alone inverter systems consist
of a standard Solar Home System with solar module, battery and solar
charge controller, plus an additional inverter that supplies AC
power. To such a system you can connect any commercial AC appliance
known from the public grid. Furthermore, it is even possible to run
DC loads. The inverter is connected directly to the battery with a
short and thick cable. Such a system can be realised as a standard
12 V system, alternatively also as a 24 V or 48 V system for higher
power demands. Due to the simple system concept, the installation is
fast and easy to do.
Q. How are
regulators used in solar/wind hybrid systems?
System overview
The main feature of a hybrid system
is the use of two or more different energy sources. For so-called
photovoltaic hybrid systems in the field of solar energy especially
a diesel generator, a wind generator or a public grid is used as an
additional source of energy. The inverters with integrated battery
charger designed for hybrid systems supply the connected alternating
current loads either out of the battery or from the second energy
source – always according to the requirements of the system. It is
also possible to recharge the battery from the additional energy
source via the battery charger. The advantage of photovoltaic hybrid
systems is that the solar generator does not have to be oversized to
supply the loads even during months with low solar irradiation. This
saves a significant amount of the initial investment. The solar
produced power is always used primarily in the system. But in
combination with the second energy source reliable AC power is
available day and night throughout the year.
Q: What are Pulse Width Modulation (PWM) Solar
Regulators?
Charging a battery with a solar pv
system is difficult. In the early days regulators were just
on-off switches that tried to prevent the plates of the battery
being destroyed, a process known as sulphation, that occurred when
solar panels produced excess energy that hand to be handled
correctly. As solar pv systems came to maturity it was clear
that a radical rethink was need on how these primitive regulators
could cope with demands for better charging. PWM has
recently surfaced as the first significant advance in solar battery
charging.
PWM solar chargers use technology
similar to other modern high quality battery chargers. When a
battery voltage reaches the regulation set-point, the PWM algorithm
slowly reduces the charging current to avoid heating and gassing of
the battery, yet the charging continues to return the maximum amount
of energy to the battery in the shortest time. The result is a
higher charging efficiency, rapid recharging, and a healthy battery
at full capacity.
In addition, this new method of
solar battery charging promises some very interesting and unique
benefits from the PWM pulsing. These include:
-
Ability to recover lost battery
capacity and de-sulphate a battery
-
Dramatically increase the charge
acceptance of the battery
-
Maintain high average battery
capacities (90% to 95%) compared to on-off regulated
state-of-charge levels that are typically 55% to 60%
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Equalize drifting battery cells
-
Reduce battery heating and gassing
-
Automatically adjust for battery
aging
-
Self-regulate for voltage drops and
temperature effects in solar systems
Q. Why is this technology important to me?
There are substantial benefits of
using PWM technology in a solar pv energy system. The benefits
include:
Longer battery life:
More battery reserve capacity:
-
increasing the reliability of the
solar system
-
reducing load disconnects
-
opportunity to reduce battery size
to lower the system cost
Greater use of the solar array
energy:
Greater user satisfaction:
(Information
courtesy of Morningstar Corporation)
OUTBACK (MPPT)
CONTROLLERThe OutBack MX60 Maximum Power Point
Tracking (MPPT) charge controller enables your PV system to achieve
its very best performance. Rated for up to 60 amps of DC
output current, the MX60 can be used with battery systems from 12 to
60V DC with PV open circuit voltage as high as 140V DC. The MX60 has
fully adjustable set points that allows it to work with virtually
any battery type, chemistry and charging profile. The MX60 allows
you to use a higher output voltage PV array with a lower voltage
battery. This is important as it reduces battery wire size and power
loss from the PV array to the battery or inverter location and
thereby maximizes the performance of your PV system. The MX60 comes
standard with an easy to use and understand display of the PV
system’s performance. The four line, 80 character, back-lit LCD
display is also used for programming and monitoring of the system’s
operation, including built-in data logging with 64 days of memory.
The MX60 can also be connected to the OutBack MATE system controller
and display to allow monitoring of up to eight MX60 controllers from
a location up to 1000 feet away. The MATE also includes an opto-isolated
RS232 port for connection to a PC for data logging and system
monitoring.
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Outback
MX60 Charge Controller |
Fox Solar Charge Controllers from SunWare
Fox Solar Regulators provide 3 stage charging to your battery
bank from solar panels with a rated power of up to 20Amps.
They are equally ideal on board yachts, for use in the home
and on professional installations providing both overcharge
and deep discharge protection for deep cycle batteries. The
range of Fox solar regulators are conveniently available in
four versions, specifically tailored to the requirements of
leisure charging applications.
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Fox Charge Controllers |
Fox 250 12V Single Battery Models.
Ideal for battery banks on board motor
homes, caravans & yachts
where a single battery bank (one or more batteries in
parallel) requires charging. Choose either the simple to
mount Surface version, only 2 fixing screws required or the
recessed version for a built in finish.
Fox 350 12/24V Dual Battery Models
The Fox 350 includes all the standard features with additional
detailed information on the LCD display including battery
state of charge percentage. This unit is ideal where 2
battery banks are
installed and typically both require top up, particularly
whilst unattended. The system’s built in logic charges
battery 1 first and ensures it has remained at the final level
of 3 stage charging for 1 hour before changing over to battery
bank 2. There’s
also
even an emergency charge function that activates charge to
battery 2 if it falls below 10.8V providing battery 1 has more
than 11.5V.
Fox Remote Display
A discreet digital display unit for remote installation from a
regulator enabling the user to view information at a secondary
location. Max distance from regulator is 3M. Available in
surface, Fox D/1 and recessed Fox D/1E models.
Fox 250 and 350 models include the following features:
• Digital display of charge and
load currents, Volts and warnings
• Soft touch keypad to scroll
through display and program settings
• Latest pulse width modulation
technology with built in temperature compensation to ensure
the most efficient battery charging
• Manual switch for controlling
loads on and off
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Reverse polarity protected and
2 year warranty
WE CAN SUPPLY
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Tel: 0208 663 3273 Fax: 0208 650 9037 email: sales@brightgreenenergy.co.uk
