Main characteristics
- Maximum power point tracking (MPPT)
- Three charging modes for optimum
operation and battery life: MPPT, boost
and float
- Temperature compensation
- Low current consumption
- Battery type selection
- Internal blocking diode
- Good electrical protection
- Large, robust screw terminals
Charging modes
Maximum power point tracking
(MPPT) charging
If a photovoltaic module is connected
directly to a battery using a normal charge
controller, a significant part of its power
may be wasted. Naps MaxPower acts as
an electrical “gear-box”, helping to get the
highest possible power from the module
when it is most needed, especially when
the battery is empty.
As an additional benefit you may in some
cases connect two modules in series to a
12 Volt battery. For example, you can start
with one module and later add a second
one connected in series with the old one,
without having to add new cabling between
the modules and Naps MaxPower.
When the battery is not fully charged,
Naps MaxPower will use MPPT charging
to get all available power from the module.
Boost charging
If the battery has been deeply discharged
large sulfate crystals start to develop in the
battery plates. At the same time, a layer of
low density acid will start to develop at the
top of the battery plates and high density
acid below the plates. These will lower the
battery capacity and shorten its life.
Both of these phenomenas can removed
by charging the battery to a higher end
voltage. This higher charging voltage will
dissolve the harmful sulphate crystals and
also mix up the acid by stirring it with the
gas bubbles that are produced at the end
of charging. Because excessive overcharg-
ing increases the battery’s water con-
sumption and causes corrosion, the
amount of boost charging depends on the
previous depth of discharge.
If the battery has been discharged to
approximately 80 % state of charge no
boost is applied and MPPT charging will
switch to float charging at 14.2 Volts. If the
battery is discharged more deeply, more
boost charging will be applied.
If the battery has been discharged to
approximately 30 % or less, the battery
voltage is increased to 15.0 Volts for one
hour before switching to float charging.
Boost charging is not recommended for
sealed (VRLA) batteries. Therefore Naps
MaxPower’s boost function can be disa-
bled with a switch on the circuit board (see
installation instructions).
Float charging
Once the battery is fully charged, Naps
MaxPower enters float charging mode
where it tries to keep the voltage at a
constant 14.2 Volts (at +25 °C ambient
temperature). In practice this means that
Naps MaxPower finishes charging the
battery with lower current and keeps it fully
charged. Also, if the loads use less power
than the module can produce, all load
current is taken from the module rather