Flexcharge NC25A-12, Manual

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There has been a great deal of discussion in the solar electric industry over the use of blocking diodes.
In an effort to clarify the topic Flexcharge
TM USA has called, met with, or gathered information pertaining to the
use of diodes from several solar panel and equipment manufacturers to verify the following information.
The following is a condensed version of the information to assist you in designing a failure resistant system.
What is a blocking diode?
A blocking diode is a one-way valve for electricity. The band on the case of the diode is the output, which should
be installed towards the battery in the positive wire from each solar panel. There are two primary types of diodes,
Schottky (sensitive to damage but low loss type) and Silicon (tough, but higher loss type). They are rated by the
amount of current that can pass through them in amps, and the amount of voltage they can withstand in reverse. .
What is the function of blocking diodes in a solar system?
1 The diode will prevent the flow of electricity into the panels when the panels are not making electricity, and
will prevent voltage spikes in the system from reaching the panels. They also prevent interaction between
each solar panel in the system. Without diodes, a shaded panel will substantially reduce the output of the
entire system.
2 A diode will prevent a damaged panel which has shorted (a common type of failure) from draining the
battery system, or drawing
power from the remaining good panels.
There are primarily three types of solar electric panel technologies being used today.
1) SINGLE CRYSTALLINE 2) POLY CRYSTALLINE 3) AMORPHOUS
How should blocking diodes be used with each type of panel?
SINGLE CRYSTALLINE panels are glass covered rigidly mounted panels. They have a low nighttime back flow of
power from the batteries. The loss at night is actually a little less than the amount of loss you get by adding a
blocking diode to the panel. On a single panel system you may get more out of your panel if you do not use a
blocking diode on these type of panels,
On multiple panel arrays, blocking diodes should be used , especially
on unattended remote systems, to guard against a failed panel. Because they are glass covered, a stray falling
branch, hailstones, a child with a rock, or bored hunter could bring the entire system down by damaging only one
panel.
POLY CRYSTALLINE panels are also glass covered rigidly mounted panels. They have a slightly higher
nighttime draw of power from the batteries when compared to single crystalline panels. The loss at night is near
equal to the loss you get by adding a blocking diode to the panel. You may or may not get more out of your panel
by using blocking diodes on these type of panels,
On multiple panel arrays , blocking diodes should be used ,
especially on unattended remote systems, to guard against a failed panel. Because they are glass covered, a
stray falling branch, hailstones, a child with a rock, or bored hunter could bring the entire system down by
damaging only one panel.
AMORPHOUS panels are a very different when compared to the other types of panels. They have a fairly
substantial nighttime draw of power from the batteries when compared to single crystalline panels. The loss at
night is higher than the loss you get by adding a blocking diode to the panel;
in addition, these type panels could
actually draw enough power from the batteries at night to damage themselves if diodes are not used. To
compensate for the diode loss, most amorphous panels have a higher operating voltage, to make up for the
voltage drop losses of the diode.
Blocking diodes should be used on all systems when panels have been connected in series to charge 24V,
or higher voltage batteries, or when using an inverter on the system. Inverters can cause voltage spikes
as high as
60 volts on the DC positive wires. This is enough voltage to damage most solar panels.
In conclusion; blocking diodes should be used on all systems except, one panel single crystalline 12V systems. If your system
is so marginal that using, or not using diodes will make the difference, consider adding another solar panel to your system.
See the previous page for a list of suggested blocking diodes for your system
READ THIS!! IMPORTANT: USING or NOT USING
BLOCKING DIODES ON YOUR PV CHARGING SYSTEM?