Charge Controllers
Charge Controllers handle the current
from your PV array and/or wind generator. They safely charge
your battery bank and/or send DC current to a direct load or
dumpload. The higher the amp rating the more panels/current you
can control via the charge controller. It is also
important to know the max voltage and system voltage
limitations of your controller so you wire your
panels/wind generators together properly and don't
exceed values. Every system requires a charge controller
to keep the batteries from over charging, gassing
and boiling. Also see,
How Charge Controllers Work in our
Learning Center
Comparing PWM and MPPT Charge Controllers
PWM Pros
- PWM charge controller are built on a time tested
technology . They have been used for years in PV
systems and are well established.
- These charge controllers are inexpensive
, usually selling for less than $250.
- PWM charge controllers are avaialble in sizes up
to 60 amps
- PWM charge controllers are durable ,
most with passive heat sink style cooling.
- These charge controllers are available in many sizes for
a variety of applications
PWM Cons
- The PV input nominal voltage must match battery bank
nominal voltage if you're going to use PWM.
- There is no single controller sized over 60 amps DC as
of yet.
- Many smaller PWM charge controller units are not UL
listed
- Many smaller PWM charge controller units come without
fittings for conduit.
- PWM charge controllers have limited capacity for system
growth.
MPPT Pros
- MPPT charge controllers offer a potential
increase in charging efficiency up to 30 %.
- These charge controllers also offer the potential
ability to have array with higher input voltage
than battery bank
- You can get sizes up to 80 amps .
- MPPT charge controller warranties are typically
longer than PWM units
- MPPT offer great flexibility for system
growth
MPPT Cons
- MPPT charge controllers are expensive, sometimes costing
twice as much as a PWM controller and are certainly more
expensive than PWM controllers.
- MPPT units are generally larger in physical size.
- Sizing an appropriate PV array can be challenging
without MPPT charge controller manufacturer guides.
- Using an MPPT controller forces the PV array to be
comprised of like photovoltaic modules in like strings.
|
Xantrex 35amp Charge Controller
with optional digital display |
 |
Xantrex C35charge controller. It
can be used as a battery charge, DC load control or DC diversion
operation and comes with a standard multi-color charge status
LED.
Voltage Configurations: 12 and 24 VDC
Max. PV Open Circuit Array Voltage:
55 VDC
PWM
|
|
Xantrex 40amp Charge Controller
with digital display |
|
Xantrex C40 charge
controller may be configured for 12, 24, or 48 VDC operation. It
can be used as a battery charge, DC load control or DC diversion
operation and comes with a standard multi-color charge status
LED. 125 Max Voltage
input
45amp Max PWM 500watt max at 12v setting 2000watt
max at 48v setting
|
|
Outback FLEXMax 60 & 80 Amp Charge Controllers |
 |
Outback
FLEXMax 60 & 80 Amp Charge Controllers
Outback is the Cadillac of charge controllers. For ease of
use and reliability.
The ability to efficiently step-down a
high voltage solar array to a low
voltage battery is one of the major
advantages of these and other MPPT
charge controllers. This feature can
save you money by reducing the size of
wire required and making the
installation simpler and faster. Since
you can often just wire up several solar
panels in series without the need of a
junction box or array combiner, wiring
is usually very simple.
Use with a 12, 24, or 48 volt
battery system
145 volt max input
Outback Flexmax 80 amp Charge Controller
Outback flexmax 60 amp Charge Controller
|
Increase Solar Charging with a Power Tracking Charge
Controller
A relatively new feature is showing up in charge
controllers. It's called maximum power point tracking (MPPT).
It extracts additional power from your PV array, under
certain conditions. This article explains the process by a
mechanical analogy, for people who do not understand basic
electricity.
The function of a MPPT is analogous to the transmission
in a car. When the transmission is in the wrong gear, the
wheels do not receive maximum power. That's because the
engine is running either slower or faster than its ideal
speed range. The purpose of the transmission is to couple
the engine to the wheels, in a way that lets the engine run
in a favorable speed range in spite of varying accelleration
and terrain.
Let's compare a PV module to a car engine. Its voltage is
analogous to engine speed. Its ideal voltage is that at
which it can put out maximum power. This is called its
maximum power point. (It's also called peak power voltage,
abbreviated Vpp). Vpp varies with sunlight intensity and
with solar cell temperature. The voltage of the battery is
analogous to the speed of the car's wheels. It varies with
battery state of charge, and with the loads on the system
(any appliances and lights that may be on). For a 12V
system, it varies from about 11 to 14.5V.
In order to charge a battery (increase its voltage), the
PV module must apply a voltage that is higher than that of
the battery. If the PV module's Vpp is just slightly below
the battery voltage, then the current drops nearly to zero
(like an engine turning slower than the wheels). So, to play
it safe, typical PV modules are made with a Vpp of around
17V when measured at a cell temperature of 25°C. They do
that because it will drop to around 15V on a very hot day.
However, on a very cold day, it can rise to 18V!
What happens when the Vpp is much higher than the voltage
of the battery? The module voltage is dragged down to a
lower-than-ideal voltage. Traditional charge controllers
transfer the PV current directly to the battery, giving you
NO benefit from this added potential.
Now, let's make one more analogy. The car's transmission
varies the ratio between speed and torque. At low gear, the
speed of the wheels is reduced and the torque is increased,
right? Likewise, the MPPT varies the ratio between the
voltage and current delivered to the battery, in order to
deliver maximum power. If there is excess voltage available
from the PV, then it converts that to additional current to
the battery. Furthermore, it is like an automatic
transmission. As the Vpp of the PV array varies with
temperature and other conditions, it "tracks" this variance
and adjusts the ratio accordingly. Thus it is called a
Maximum Power Point Tracker.
What advantage does MPPT give in the real world? That
depends on your array, your climate, and your seasonal load
pattern. It gives you an effective current boost only when
the Vpp is more than about 1V higher than the battery
voltage. In hot weather, this may not be the case unless the
batteries are low in charge. In cold weather however, the
Vpp can rise to 18V. If your energy use is greatest in the
winter (typical in most homes) and you have cold winter
weather, then you can gain a substantial boost in energy
when you need it the most!
Here is an example of MPPT action on a cold winter day:
Outside temperature: 20°F (-7°C) Wind is blowing a bit,
so the PV cell temperature rises to only around 32°F (0°C).
Vpp = 18V Batteries are a bit low, and loads are on, so
battery voltage = 12.0
Ratio of Vpp to battery voltage is 18:12 = 1.5:1
Under these conditions, a theoretically perfect MPPT
(with no voltage drop in the array circuit) would deliver a
50% increase in charge current! In reality, there are losses
in the conversion just as there is friction in a car's
transmission. Reports from the field indicate that increases
of 20 to 30% are typically observed.
|
