Operation
ProStar MPPT Operator’s Manual
37
36
4.0
High Voltage Strings and Grid-tie Modules
Another benefit of TrakStar MPPT technology is the ability
to charge 12 or 24 volt batteries with solar arrays of higher
nominal voltages. A 12 volt battery bank can be charged
with a 12, 24, 36 or 48V nominal off-grid solar array. Certain
grid-tie solar modules may also be used as long as the solar
array open circuit voltage (V
oc
) rating will not exceed the
ProStar MPPT 120V maximum input voltage rating at worst-
case (lowest) module temperature. The solar module docu-
mentation should provide V
oc
vs. temperature data.
Higher solar input voltage results in lower solar input cur-
rent for a given input power. High voltage solar input strings
allow for smaller gauge solar wiring. This is especially help-
ful for systems with long wiring runs between the solar array
and the ProStar MPPT.
An Advantage Over Traditional Controllers
Traditional controllers connect the solar module directly
to the battery when recharging. This requires that the so-
lar module operate in a voltage range that is below the
module’s V
mp
. In a 12V system, for example, the battery
voltage may range from 10 - 15 Vdc but the module’s V
mp
is
typically around 17V. Figure 4.1 shows a typical current vs.
voltage output curve for a nominal 12V off-grid module.
Figure 4.1. Nominal 12 volt solar module I-V curve and output power
graph
PO
WER
VOLTAGE
10
15 17
TrackStar
Maximum
Power
Point
Traditional
Controller
Operating Range
CURRENT
VOLTAGE
10
15 17
Maximum
Power
Point
Typical Battery
Voltage Range
12 Volt Module
Current vs. Voltage
12 Volt Module
Output Power
4.2 Battery Charging Information
4-Stage Charging
The ProStar MPPT has a 4-stage battery charging algorithm
for rapid, efficient, and safe battery charging. Figure 4-2
shows the sequence of stages.
NIGHT
NIGHT
BULK
CHARGE
ABSORPTION
FLOAT
EQUALIZE
VOL
TAGE
TIME
Figure 4.2. ProStar MPPT Charging Algorithm
Bulk Charge Stage
During Bulk charging, the battery is not at 100% state of
charge and battery voltage has not yet charged to the Ab-
sorption voltage set-point. The controller will deliver 100%
of available solar power to recharge the battery.
Absorption Stage
When the battery has recharged to the Absorption voltage
set-point, constant-voltage regulation is used to maintain
battery voltage at the Absorption set-point. This prevents
heating and excessive battery gassing. The battery is
allowed to come to full state of charge at the Absorption
voltage set-point. The green SOC LED will blink once per
second during Absorption charging.
