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When mounted vertically as described in the installation section, the unit can deliver full output in an ambient temperature of up
to 40°C (104°F). If an over temperature condition exists, the unit will cycle on/off, reducing average power delivery to within safe
limits. During periods of thermal shutdown the Charge Status Indicator will display an "off" condition.
MAXIMUM POWER POINT TRACKING (MPPT)
MPPT and associated current boost operation is fully automatic and will function whenever sufficient PV current is available.
The unit requires a minimum PV input current of approximately 2.5A for the MPPT system to operate and raise PV voltage to the
optimum value where the PV array can produce maximum power. The percent increase in output charge current relative to charge
current that would be seen with a conventional charge controller is variable, and will change with operating conditions. Output
current will vary as available PV power changes with operating conditions.
The principal operating conditions which affect current boost performance are battery voltage and PV array temperature. At
constant solar intensity available PV array power changes with array temperature. A PV array's power vs. temperature
characteristic is such that a cool PV array can produce a higher voltage and more power, than a hot PV array. When PV current is
sufficiently high for MPPT to operate, a constant power output is delivered to the battery. Since output power is constant while
MPPT is operating, a decrease in battery voltage produces an increase in charge current. This means that the greatest current
increase occurs with a combination of cool ambient temperature and low battery voltage. The unit delivers the greatest charge
current increase when you need it most, in cold weather with a discharged battery.
Because output power is constant while boost is operating, anything that leads to lower battery voltage will produce an
increase in output charge current. While a discharged battery is one way to produce lower output voltage, and therefore higher
output current, other normal conditions may produce lower voltage as well. Any DC power consumption during the day will
decrease net battery charge current, which decreases battery voltage. Operating a large inverter or application of other heavy loads
can produce substantial drops in output voltage leading to significant increases in output current. Additionally, anything that can be
done to lower PV array temperature will also lead to increased charge current by increasing PV power production. Installing
modules in a breezy location for example will cool the PV array due to increased air circulation.
HOW MPPT WORKS
A PV module is a constant current device. A typical PV module voltage vs. current curve shows current remains relatively
constant over a wide range of voltage. A typical 75 watt module is specified to deliver 4.45 amps @ 17 volts @ 25°C. Conventional
PV controllers essentially connect the PV array directly to the battery when battery voltage is low. When a 300 watt series/parallel
array of four 75 watt modules are connected in the normal fashion directly to a battery charging at 24 volts, the modules still provide
approximately the same current. But, because output voltage of each of the two series strings is now held artificially low at 24 volts
by the battery rather than 34 volts (2x17V), each series string only delivers 107 watts (24V x 4.45A) for a total power delivered to
the battery of 214 watts. This system delivers only 8.90 amps (2 x 4.45A) of charge current while wasting 86 watts of available
power.
Solar Boost 6024H's patented MPPT technology operates in a very different fashion. Consider a system where the four 75
watt modules are connected in series for a nominal 48 volt input, charging the same 24 volt battery. Under these conditions Solar
Boost 6024H calculates the maximum power voltage (V
It then operates the PV module string at 4x17 volts or 68 volts which extracts maximum power from the modules. Solar Boost
6024H continually recalculates the maximum power voltage as operating conditions change. Input power from the MPPT controller,
in this case full 300 watts, feeds a switching type power converter which reduces the 68 volt input to battery voltage at the output.
The full 300 watts which is now being delivered at 24 volts would produce a charge current of 12.5 amps. A charge current increase
of 3.6 amps or 40% is achieved by converting the 86 watts that would have been wasted into useable charge current. Note that this
example assumes 100% efficiency to illustrate the principal of operation. In actual operation, charge current increase will be
somewhat less as some available power is lost in wiring, connections, and in Solar Boost 6024H.
TYPICAL CURRENT BOOST PERFORMANCE
As described above, current boost performance for a particular installation varies primarily with PV array temperature and
battery voltage. Two other factors which affect boost performance include system wiring and PV module design. The effect
wiring has on performance is power wasted heating undersized wiring is unavailable for charging. This is discussed further in
the Battery And PV Wiring section. The effect PV module design has on performance is 36 cell modules with a maximum power
voltage (V
) of 17 volts or higher will tend to produce more boost, whereas modules with V
MP
produce less boost. Module types with a high V
there is more typically untapped power to be extracted. For a 24 volt system using eight 75 watt modules in series with peak
power specifications of 4.45 amps @ 17 volts @ 25°C, representative boost performance under a variety of operating
conditions is shown in Table 2. Your current boost performance will vary due to a variety of factors. What you can be sure of is
that Solar Boost 6024H will deliver greater total charge current when conditions are such that the modules have extra power to
extract.
) at which the PV module delivers maximum power, in this case 17 volts.
MP
value in the range of 17.0−18.5V provide the best boost performance since
MP
Installation and Operation Manual
less than 17 volts will tend to
MP
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