Windy Nation TrakMax 40 MPPT Solar Charge Controller - Manual (Page 13)

TrakMax 40 User Manual
Revision 1.0
power, than a hot PV array. When PV voltage 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 corresponding 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.
Additionally, anything that can be done to lower PV array temperature will also lead to increased charge
current by increasing PV power production. In cool/comfortable temperatures and typical battery states of
charge, most systems see about 10 – 20% increase. Charge current increase can go to zero in hot
temperatures, whereas charge current increase can easily exceed 30% with a discharged battery and
freezing temperatures.
Figure 4.1: Current / Power vs. Voltage Characteristics
4.1.1 How MPPT Works
A PV module is a constant current type device. As shown on a typical PV module voltage vs. current curve,
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 cell temperature. Conventional PV controllers essentially connect the
PV array directly to the battery when the battery is discharged. When a 75 watt PV module is connected
directly to a battery charging at 12 volts, the PV module still provides approximately the same current. But,
because output voltage is now at 12 volts rather than 17 volts, the PV module’s power production is
artificially limited and the 75W PV module only delivers 53 watts. This wastes 22 watts of available power.
TrakMax’s MPPT technology operates in a very different fashion. Under these conditions TrakMax calculates
the maximum power voltage (V) at which the PV module delivers maximum power, in this case 17 volts. It
then operates the PV module at 17 volts which extracts maximum available power from the PV module.
TrakMax continually recalculates the maximum power voltage as operating conditions change. Input power
from the maximum power tracking controller, in this case 75 watts, feeds a switching type power converter
which reduces the 17 volt input to battery voltage at the output. The full 75 watts which is now being
delivered at 12 volts would produce a current of 6.25 amps. A charge current increase of 1.8 amps or 40% is
achieved by converting the 22 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, the power boost
will be somewhat less.
4.2 C HARGE M ODE
4.2.1 Factory Default Settings
Charge Mode Three (3) Stage
Absorption Voltage 14.4V 28.8V
Bulk Voltage 14.6V 29.2V
Float Voltage 13.4V 26.8V
Equalize 14V 28V
Page 13 of 20 windy nation 03/06/2013