SMP100 Manual

8
System Calculations
Loads
The rst step in planning a PV system is to determine the load. What is the power intended
for? How much power will be required and for how long? There are many resources available
in print and on-line to help determine average and peak load requirements. It is recommended
that you use these resources to calculate anticipated load requirements and that your system
planner design for load growth. Experience has shown that loads rarely remain static over
time, and most often increase. Once the load characteristics are determined your system
planner can make decisions about the appropriate battery voltage, and hence the number and
arrangement of batteries that can meet the anticipated demands. This leads to the charging
current and voltage needed from the SolarMax to charge the batteries.
Maximum Voc
The maximum operating input voltage of the SolarMax is 230 volts. Above this voltage the
unit will shut down to avoid damage. The absolute maximum input voltage the controller can
accept without damage is 250 volts. In practice the actual voltage should never reach the Voc
point as SolarMax will be loading the array down to the Maximum Power Point at all times
unless the batteries reach full charge and will not accept any more charge current.
Conversion Efciency
The conversion efciency of the SolarMax in the proposed conguration must be considered.
The table below shows the minimum Vmp and recommended Vmp (Maximum Power Voltage)
for each battery voltage as well as the recommended array power. Also keep in mind not to
exceed the maximum open circuit voltage in any array conguration.
Nominal
Battery
Volts
Battery
Float
Volts
Battery
Absorption
Volts
Maximum
Output
Power
(Watts)
Recommended
Array Power
(Watts)
Minimum
Maximum
Power Voltage
(Vmp)
Recommended
Maximum
Power Voltage
(Vmp)
Maximum
Open Circuit
Voltage
(Voc)
24 27.2 28.8 2880 3000 30 Volts 55 Volts 230 Volts
28 31.7 33.6 3360 3500 35 Volts 62 Volts 230 Volts
36 40.8 43.2 4320 4500 45 Volts 80 Volts 230 Volts
48 54.4 57.6 5760 6000 60 Volts 106 Volts 230 Volts
60 68.0 72.0 7200 7500 75 Volts 133 Volts 230 Volts
72 81.6 86.4 8640 9000 90 Volts 160 Volts 230 Volts
Every brand of panel is different, so ensure you are familiar with your panels’ specications.
Also be aware that weather and temperature will affect the Voc of your panels. A higher
temperature will produce a lower Voc and lower Vmp voltage, while lower temperatures